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Studies on Danish entoprocta Claus Nielsen
a
a
Marine Biological Laboratory , Heisingør , Denmark Published online: 20 Feb 2012.
To cite this article: Claus Nielsen (1964) Studies on Danish entoprocta, Ophelia, 1:1, 1-76, DOI: 10.1080/00785326.1964.10416272 To link to this article: http://dx.doi.org/10.1080/00785326.1964.10416272
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OPHELIA, 1964, 1 (1): 1-76
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STUDIES ON DANISH ENTOPROCTA By CLAUS
NIELSEN
Marine Biological Laboratory, Heisinger, Denmark
CONTENTS Page I. Abstract
1
L. phascolosomata
2. Materials and methods..................
2
L. [auveli L. compressa
3. Survey of the literature on the Danish Entoprocta 4. Systematic survey of the Danish Entoproct fauna Fam. Loxosomatidae Loxosoma L. pectinaricola L. rhodinicola ..................•..... L. signijicans L. agile Loxosomella L. elegans L. simi/is L. polita . '" .. , . ... . .. .. .. .. .. . • L. ornata L. marsypos L. harmeri . .. .. .. .. .. .. . L. atkinsae L. nitschei L. murmanica
4 5 6 6 7 9
II 13 16 18 20 22 24 27 28 30 32 32
L. nordgaardi L. glandulijera L. discopoda L ..vcaura L. varians
Fam. Urnatellidae Fam, Pedicellinidae Pedicellina P. cernua P. nutans Barentsia B. gracilis B. laxa
Page 37 . 39 .
.. . . . .
41
42 45 47 47
. 49 . 52 . 53 . 54 . 54 . 56 . 56 . 56 . 57
5. Systematics of the Loxosomatidae
59
6. Ecology of the Loxosomatidae ......
62
................................
71
8. References ..............................•
73
7. Discussion
1. ABSTRACT A survey of the literature on the Danish Entoprocta is given. Descriptions and figures are given of all Entoprocta, viz. 24 species, recorded from Danish waters. Seventeen of these are new to the Danish fauna, and eight are new to science. The members of the Loxosomatidae have been especially studied, and their systematics revised. The two genera Loxosomella and Loxocalyx are united into one under the name of Loxosomella, and this genus and Loxosoma are both divided into two subgenera. Based in part on the new species, the phylogenetic trends within the Loxosomatidae are discussed. Considering the association between all the species described and their hosts, it is concluded that the Loxosomatidae are energy commensals which secure their food by filtering it from the water currents made by their host animals. Observations on the periods of reproduction of the Loxosomatidae seem to show that the majority of the species reproduces all year round.
2
CLAUS NmLSEN
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2. MATERIALS AND METHODS The material on which the present study is based comes from the author's own collections made at Heisinger, Frederikshavn, Lese, and Kristineberg (see Fig. 1) as well as from the collections of the Zoological Museum, Copenhagen; Naturhistoriska Museet, Goteborg; Naturhistoriska Riksmuseet, Stockholm; Zoologiska Institutionen, Lund; Zoologiska Institutionen, Uppsala; and Zoologisk Museum, Oslo; in addition, Mr. Erik Rasmussen, M. Sc., kindly informed me of the finding of Pedlcellina cernua (Pallas) and Barentsia gracilis (Sars) in the Isefjord and the Copenhagen South Port. The descriptions of two of the new species, viz. Loxosoma agile and Loxosomella slmilis, are based on specimens found by the author during a stay at the Espegrend Biological Station, W-Norway; a special paper on the Entoprocta found in the vicinity of that station will be published elsewhere. All the author's finds from the Sound (0resund) were dredged from the deeper parts where salinity is high (cf. Brattstrom, 1941). During the work of collecting by the author, Loxosomatidae were systematically looked for on Sipunculidae, Bryozoa, Spongia, etc., and especially the Polychaeta and their tubes which often turned out to be habitats of this family. Of the collections of the various museums not only the materials of Entoprocta, which proved to consist chiefly of Pedicellinidae, were examined, but also species of invertebrates known from earlier collections to be hosts of Loxosomatidae. To facilitate the drawing and fixation of extended individuals various anaesthetics were used, e. g. magnesium sulphate, propylene-phenoxetol, cocalne, and stovaine, of wbich the last-mentioned proved to be the most quickly acting and the most reliable. For fixation, Bouin's fluid (Romeis § 315) was used; it preserves the animals well, though the lophopbore of extended individuals will often be bent strongly backward. After fixation for about one hour, the individuals were transferred to 70 per cent alcohol, in which they were kept. In examinations of Loxosomella nordgaardi Ryland on Bryozoa, the method of colouring the whole colony in a weak borax carmine solution, mentioned by Ryland (1961 b p. 34), was employed; by this method the entoprocts will be coloured red, while the calcified bryozoan colony will remain almost entirely white. All the drawings were executed by means of a Leitz Greenough dissection microscope with drawing apparatus; a few details, however, were seen with other microscopes. The measurements were made by means of an ocular micrometer. As regards the Loxosomatidae, the totallengtb was reckoned from the uppermost point of the tentacular membrane between the two aboral tentacles to the point of attachment of the peduncle or to the sheele of tbe foot.
3
STUDIES ON DANISH ENTOPROCfA
...
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In cases in which the calyx was not sharply marked off from the peduncle, the under side of the stomach was regarded as the boundary between the peduncle and the calyx. For all the species, extended individuals seen in frontal, posterior, and lateral views, as well as a contracted individual and an individual with a big bud, were drawn whenever possible. In most cases the drawings were made
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4
CLAUS NIELSEN
from living anaesthetised individuals viewed by transmitted light, alternating with incident light; finally, the animals were fixed in Bouin's fluid, which made some details appear more distinctly, and these were then inserted in the drawing. The drawings based on fixed material are marked by an asterisk. The fresh material collected, including holo-types of new species, will be transferred to the Zoological Museum, Copenhagen, except the holo-types of Loxosoma agile and Loxosomella similis which are kept in the Zoological Museum, Bergen, Norway. I wish to thank the staff of the Marine Biological Laboratory, Helsinger, above all Professor G. Thorson, Ph. D., for much encouragement, help, and hospitality during my stays at the laboratory and my trips with the ~Opheliac:. I also tender cordial thanks for all help rendered during my collecting trips to the University Laboratory, Frederikshavn, the Kristineberg Zoological Station in Sweden, and the Biological Station, Espegrend, Norway. I am likewise indebted to the following persons, who kindly placed material at my disposal during my studies: Mrs. E. Wesenberg-Lund, M. Sc. (Zoological Museum, Copenhagen), Messrs. B. Hubendick, Ph. D.. and S. Svard (Natural History Museum, Gothenburg). Dr. A. Franzen (Zoological Institution, Uppsala), Professor E. Dahl, Ph. D., and Dr. Y. Lowegren (Zoological Institution, Lund) and Dr. N. Knaben (Zoological Museum, Oslo); the very fine collections from the museum at Gothenburg were of special importance for the elucidation of the distribution of the various species. Finally, I wish to thank Mr. E. Rasmussen, M. Sc.• for information on the finding of Entoprocta in the Isefjord and the South Harbour of Copenhagen. The Rask-j2)rsted Foundation has offered a grant for the translation of the paper into English, which was done by Miss E. Gleerup. Dr. J. S. Ryland has kindly read the manuscript.
3. SURVEY OF THE LITERATURE ON THE DANISH ENTOPROCTA Entoprocta were first reported from Danish waters by Orsted (1844 p. 82), who mentions Pedicellina cernua (Pallas) (as P. echinata) and Barentsia gracilis (M. Sars) (as Pedicellina sr-) found on a Dentalium from ~Regio Buccinoideorume near Kullen. Further finds of these species are recorded by Smitt (1871), Winther (1877), Mobius (1884), and Levinsen (1891 and 1894); Levinsen in addition records the finding of Loxosomella phascolosomata (Vogt) on Goliingia vulgare (de BIainville), and of a »Loxosoma singulare Kefersteine on Crisia . eburnea Linne; the described material of the last-mentioned loxosomatid is found in the Zoological Museum, Copenhagen, and has been identified as Loxosomella nordgaardi Ryland. Lonnberg (1898) mentions »Loxosoma phascolosomatum« on the posterior part of Phascolion strombi (Montagu) from the Sound; no doubt, we are here concerned with Loxosomella nitschei (Vigelius), which is to be found on almost all Phascolion specimens from the Sound. Additional finds of the various species already mentioned are reported in the papers by Lonnberg (1903), Theel (1907), Johansen (1913), and Kramp (1918).
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STUDIES ON DANISH ENTOPROCTA
5
Mortensen (1924) states that a Loxosoma species may often occur on the under side of the disc of Amphilepis norvegica Ljungman, and this is no doubt Loxosomella discopoda Nielsen & Ryland, which has been found on this host in the Bergensfjord and in Skagerak near the Norwegian coast. Becker (1936) reports the finding of Pedicellina cernua from the western Baltic, and finally Loxosomella phascolosomata on Goliingia and an unnamed entoproct on Phascolion are reported by Wesenberg-Lund (1939). Marcus (1940) in ~Danmarks Faunae gives a complete summary of our knowledge at that time of the Danish entoproct fauna. The folIowing species are mentioned: Pedicellina cernua and P. nutans DalyelI (this species, however, has only been found off the coast of Schleswig, but it is, no doubt, this record which forms the basis of the record of P. nutans from Denmark by Prenant & Bobin (1956», Barentsia gracilis, Loxosomella phascolosomata and L. nordgaardi (as Loxosoma singulare, see above). Thorson (1946) figures a loxosomatid larva under the name of Loxosoma singulare, but, since this species has only been found near France, it is no doubt another species, though it is impossible to say which. In a popular article Brattstrom (1947) mentions the distribution of Barentsia gracilis and »Loxosoma phascolosomatum on Phascolion strombi« in the Sound; and Bock (1950) reports Pedicellina cernua and Barentsia gracilis from the western Baltic. Wesenberg-Lund (1950) states that in addition to the species already mentioned, entoprocts may occur in worm tubes and on the elytra of Polynoidae; finally, Franzen (1962) describes three new Loxosomatidae, viz. Loxosoma pectinaricola, L. rhodinicola, and Loxosomella glanduliiera from the Gullmar Fjord near Kristineberg. Thus the rather comprehensive literature on Danish Entoprocta contains, in addition to Franzen's three new species, correct records of three species: Pedicellina cernua, Barentsia gracilis, and Loxosomella phascolosomata, and the species recorded under the name of Loxosoma singulare which could be identified as Loxosomella nordgaardi. 4. SYSTEMATIC SURVEY OF THE DANISH ENTOPROcr FAUNA As mentioned above, only six species of Entoprocta are known from the area treated here, and since no less than twentyfour species were distinguished in the present investigation, it seems reasonable to give a complete account of alI the Danish species of Entoprocta. In the folIowing survey alI the species are therefore described and figured, and keys for determination are given for all the Danish species. As a rule, lists of earlier literature on the individual species are not included as, for the majority of them, such lists are to be found in the .,Faune de France: Bryozoaires Ie (prenant & Bobin, 1956).
6
CLAUS NIELSEN
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Key to the families of Entoprocta. I. Salt or brackish water forms; either solitary or colony-forming. with creeping stolons; anus, nephridia. and genital organs opening separately in the atrium .. 2 - Fresh water forms; colony-forming; from a small basal disc issue 2-3 beadstring-shaped peduncles, from wbose individual segments several calyces directly arise; anus, nephridia, and genital organs opening into a cloaca . ....................... Fam. Urnatellidae 2. Solitary forms with budding from the front of the calyx; peduncle not separated from calyx by a constriction Fam. Loxosomatidae - Colony-forming forms with budding from creeping, branched stolons; peduncle separated from calyx by a constriction Fam. Pedicellinidae
Page
S2 6 S3
Fam.l.OXOSOMATIDAE.
Solitary Entoprocta with budding from the front of the calyx. Peduncle and calyx not separated by constriction. All the species occur in salt water, and the majority of them are associated with other invertebrates. The systematics and ecology of the family are treated in chapters 5 and 6 (pp. 59 and 62). Key tot h e g e n era
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l. Calyx attached to the substratum by a peduncle 2 Calyx attached directly to the substratum, a peduncle being completely absent .................................................................................... [Loxomespilon] 61 2. Peduncle terminating basally in a muscular sucking disc with scattered glandular cells; throughout their life the animals are free and capable of moving on the substratum Loxosoma 6 - Peduncle of buds terminating basally in a differentiated foot with a pedal gland and a pedal groove with accessory glandular celIs; in some cases the differentiated foot is preserved. while in other cases it is reduced more or less completely after cementing the animal to the substratum by its secretion. . . . . . . . .• Loxosomella 16
Loxosoma Keferstein, 1862 The distinct peduncle terminates basally in a muscular sucking disc with scattered glandular cells. During their whole life the individuals are capable of moving on the substratum. All the species which can be definitely said to belong to this genus were found together with Polychaeta.
I.
2. 3. -
Key to the Danish species of Loxosoma LHost animals ill square brackets] Page Peduncle almost as long as calyx, or longer 2 Peduncle very short 3 10-16 tentacles, peduncle flattened [Pectillaria] L. pectinaricola 7 8 tentacles, peduncle round [NicomacheJ L. agile 13 Calyx with distinct lateral wings [Rhodine] L. rhodinicola 9 Calyx without lateral wings [Asychis] L. signijicans 11
STUDIES ON DANISH ENTOPROCTA
7
Loxosoma pectinaricola Franzen, ]962
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Fig. 2 Large species, total length most often up to about 2 mm, occasionally even up to about 4 mm. Peduncle generally one to two times as long as calyx, but in large individuals the peduncle may be up to eight times the length of the calyx. These very long-stalked individuals occur in few populations only, and even then, there is as a rule only one or two individuals in each population. Calyx distinctly flattened, almost twice as long as wide. Lophophore big, directed forward, with 10-16 tentacles, of which the oral may be a little longer than the aboral ones. Stomach big, rounded square, with a big expansion basally at the point of transition of the oesophagus; when the animal is expanded, the stomach is almost square, while in a contracted condition it is only about half as high as wide. When the animal is extended, the calyx passes more or less evenly into the peduncle, but it is sharply marked off from it when the animal is contracted. Peduncle somewhat flattened, sometimes with slightly concave front side; in the very long-stalked individuals it can be spirally coiled. Pedal disc oval, with numerous glandular cells, of which the central ones are the most distinct. Measurements of twenty big living individuals of the normal type (standard deviations in parentheses): Total length Length of calyx .. . . . .. .. . . .. . . .. .. .. .. .. . .. . .. . . . .. . . .. . .. .. . . . Width of calyx Depth of calyx Length of peduncle Width of peduncle _. . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . Depth of peduncle .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Length of calyx!length of peduncle................................ Length/width of calyx Width/depth of peduncle .. . . .. . .. . .. .. . . . . . .. .. .. .. .. . . .. .. . . .. .
1240 (129) II 559 (41) II 293 (28) II 147 (9) !I 686 (138) II 123 (20) II 70 (14) It 0.84 (0.16) 1.92 (0.16) I. 72 (0.21)
The buds arc formed antero-laterally on a level with the upper side of the stomach, pointing laterally. Well-grown buds have 10-12 tentacles and a total length of about 400 It, with the peduncle of almost the same length as the calyx. Maximum number of buds observed: 3 + 3, of embryos: 10. Buds: ApriJFebruary; embryos: June-February. Loxosoma pectinaricola has been found on almost all the individuals of Pectinaria belgica (Pallas) examined, and even where the latter species occurs in company with other Pectinariidae, as e. g. Amphictene auricoma (0. F. MUlIer) and Lagis koreni Malmgren, L. pectinaricola has never been found on species other than Pectinaria belgica. Often several hundred individuals are found on each Pectinaria, most numerously on the gills and the most anterior and most posterior portions of the ventral side, but they may be found all over the host; on the ventral side the Loxosomatidae are uniformly orientated, with the openings of the lophophores facing towards the anterior end of the worm.
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Fig. 4. Loxosoma rhodinicola. A, expanded individual with rather small lateral wings seen from the front; B*-C*, expanded individual seen in profile and in posterior view respectively. with embryos; D*, much contracted individual in frontal view. with one bud.
The buds are formed antero-Iaterally in front of the wings on a level with the upper part of the stomach. The only bud of moderately large size had a total length of about 175 ll; the smallest free individual measured about 360 II. Only few individuals with buds were seen, maximum number 1 + 1; the number of embryos, however, is often large, up to ten in each individual; if a large number of embryos are present, the hind wall of the atrium is forced back-
II
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STUDIES ON DANISH ENTOPROCTA
wards, forming a large bulge, as in Loxosomella obesa (Atkins, I932a). Buds: January, June-September; embryos: June-August. Loxosoma rhodinicola has been found commonly on the maldanid Rhodine loveni Malmgren, in a number of up to 275 individuals, which are usually concentrated on the first segments. The Danish finds are from muddy bottom, 25-400 m (Fig. 5). Previously the species has only been known from Kristineberg (Gullmar Fjord). The record of loxosomes on Rhodine loveni from the Gullmar Fjord by Arwidsson (1906) has reference to this species. I'
t'
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13'
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Fig. 5. Localities of Loxosoma rhodinicola.
Loxosoma signiiicans sp. n. Fig. 6 Holotype: Specimen found on Asychis biceps (M. Sars); SE of Syrodde, Lese (57° 13' N, 11°22' E), mud with sand, stones and shells, 40-42 m, 5-7-1960; deposited in the Zoological Museum, Copenhagen.
Small species, total length up to about 420 11. Peduncle quite short, about one-seventh the length of the calyx, Calyx distinctly antero-posteriorly flattened, about one and a half times as long as wide. Behind the lophophore there
12
CLAUS NIELSEN
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is a strong projecting rim, which, when the animal is contracted, appears as a brim above und upon the sides of the lophophore. Lophophore big, forwarddirected, with (18) 9-12 tentacles, stomach medium-sized, rounded, most often
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Loxosoma agile was found in the tube of Nicomache trispinata where it occurs in a number of up to 20 individuals in each tube. The individuals are very agile and frequently make nodding movements with the calyx, or they retract the peduncle to form a spiral coil. Sometimes they move slowly over the substratum (see Fig. 9), the calyx being bent down along the pedal disc, which detaches itself from the substratum, and while the peduncle is straightened, the animal slides slowly across the substratum with the peduncle in front by the ciliary movements of the pair of oral tentacles. The animal is at the same time pressed towards the substratum by the ciliary movements of the remaining tentacles (Fig. 9: 4-5); after a short space of time the peduncle is bent backward, and the animal attaches itself by the pedal disc and rises again. Such active local movements have so far only been known from L. saltans, which, however, moves by a kind of jump. The few Danish finds are from mixed bottoms with stones, 30-50 m (Fig. 7).
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16
CLAUS NIELSEN
----+
2
3
4
5
6
7
Fig. 9. Loxosoma agile. Movements (see text).
Loxosomella Mortensen, 1911 (including Loxocalyx Mortensen, 191], see p. 59) In the buds the peduncle terminates basally in a differentiated foot with a pedal gland and a pedal groove with accessory glandular cells. In some species the differentiated foot continues to exist in the adult animal, which is accordingly free and capable of moving on the substratum; in other cases, however, the foot will be more or less completely reduced, after the pedal gland has cemented the under side of the peduncle to the substratum. In cases in which the foot is completely reduced, the animal resembles a Loxosoma, and from fixed material it may be difficult to decide whether the animals originally were cemented to or merely sucked on to the substratum; this is the reason why several species cannot be referred definitely to the right genus (see p. 59).
1. 2. 3. 4. 5. 6. 7.
-
Key tot h e 0 ani s h s p e c i e s 0 r Lox 0 s 0 m e /I a. Page [Host animals in square brackets]. With 6-8 tentacles 2 With 10-18 tentacles 12 Calyx and peduncle with a row of scattered glandular cells on the front side [Pantllalis] . L. glandulijera 45 Calyx and peduncle without glandular cells on front 3 Calyx laterally compressed or almost as wide as thick 4 Calyx distinctly antero-posteriorly flattened 7 Calyx almost as thick as wide; 8-13 tentacles [Aphrodita] L. [auveli 39 Calyx distinctly compressed; 6-8 tentacles................................................ 5 Peduncle with a large adhesive disc at base; 6 tentacles [Amphilepis]. L. discopoda 47 Peduncle with no adhesive disc; (6-) 8 tentacles 6 Peduncle long, distinctly thicker at top than at base; 8 long slender tentacles [Lagisca, Guttyana] L. compressa 41 Peduncle usually short, cylindrical; (6-) 8 rather short tentacles [Nephtys. Aglaophamusi L. varians 49 Peduncle terminating basally in a foot with lateral wings, which in contracted individuals are very conspicuous; foot lacking pedal duct and accessory glandular cells, pedal gland generally divided into a pair of small cell lumps, which in certain cases may be entirely absent [Eunice] L. marsypos 27 If the peduncle terminates basally in a foot, this has no lateral wings 8
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STUDIES ON DANISH ENTOPROcrA 8. Calyx with a sharp projecting edge around the posterior side [Bryozoa] ...•.... ...................................................................................... L. nordgaardi - Calyx without sharp edges 9 9. Generally with a well developed foot; calyx and peduncle with an indistinct Yshaped row of whitish, somewhat projecting cells on their back [Petaloproctus, Nicomaclte, Rhodine] L. polita Without foot and Y-shaped cell row 10 L. atkinsae 10. Buds developing far down on the calyx; 8-12 tentacles [Phascolion] - Buds forming on a level with the upper part of the stomach; 8 (-9) tentacles 11 11. Peduncle with thick ringed cuticle; often with cuticular spines on lower comers of calyx [Phascolion] L. murmanica - Peduncle with thin glabrous cuticle; calyx without spines [Phascolion, Amphictene, Bryozoa] L. nitschei 12. Calyx with a distinct row of whitish glandular cells along its edge [Thelepus] . .. .. .. ... .. .. ... . ........ . ..... ....... ..... . . ... .. . . .. . L. ornata - Calyx without cells along its edge 13 13. Peduncle ending basally in a foot with lateral wings, which in contracted individuals are highly projecting; foot lacking pedal duct and accessory glandular cells, and pedal gland most often split up into a pair of small cell lumps, which in L. marsypos certain cases may be entirely absent [Eunice] - If peduncle terminates basally in a foot, the latter has no lateral wings ......... 14 14. With lateral sense organs and a more or less distinct Y-shaped row of whitish, slightly projecting cells on back of peduncle and calyx IS - With no Y-shaped cell row; with or without small nonprojecting lateral sense organs 17 IS. With projecting lateral sense organs and a more or less projecting rim behind the aboral margin of the lophophore; calyx with an upper, flattened portion and a lower, almost cylindrical portion 16 - With small hardly projecting lateral sense organs; no rim behind the lophophore; L. polita calyx flattened. [Petaloproctus, Nicomache, Rhodine] 16. With 10-13 tentacles; total length up to about 670 fl.; the free individuals have a pair of characteristic adhesive papillae at the tip. [Praxille/la, Rhodine, Nicomaehe?) L. elegans - With 10-11 tentacles; total length up to about 415 fl.; the free individuals have no special adhesive papillae at the tip of the foot. [Nieomaehe] ......... L. similis 17. Calyx with small papillae along aboral margin; peduncle with rudimentary, but L. harmeri distinct pedal gland [Gatryana] - Calyx without papillae; peduncle without gland 18 18. Peduncle slightly antero-posteriorly flattened, with a larger or smaller posterior L. seaura expansion at the base [Nephrys] - Peduncle round, without expansion at the base 19 19. Calyx almost as thick as wide [Aphrodita] L. fauveli - Calyx distinctly flattened 20 20. Buds forming on a level with the upper part of the stomach; peduncle often very L. phascolosomata long and stout; 10-18 tentacles LGolfingia] - Buds forming far down on the calyx, peduncle not exceeding one and a half times the length of the calyx; 8-12 tentacles [Phascolion] L. atkinsae
17 Page 42
22 30
32 32 24
27
22
18 20 28
47 39
37 30
18
CLAUS NIELSEN
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Loxosomella elegans sp. n. Fig. 10 Holotype: Specimen found in the tube of Praxillella praetermissa (Malmgren); 0resund: Off Odinsb~j (560 06' N, 120 32' E), sandy mud. 28 rn, 3-1-1962; deposited in the Zoological Museum, Copenhagen.
Medium-sized species, total length up to about 670 ~l. Peduncle rather short, thick, at the base either directly attached to the substratum or provided with a strong foot. Calyx divided into an upper broad, much flattened part and a lower, almost cylindrical portion, which are separated by a distinct constriction; the lower part passes gradually into the strong peduncle. Behind the lophophore there is a strong projecting rim, which on a level with the lower edge of the lophophore is terminated by a pair of big sensory papillae. Lophophore very big, directed forward, with 10-13 tentacles. On back of peduncle and calyx a more or less distinct Y-shaped row of slightly projecting whitish cells, the outer branches reaching almost to the sensory papillae. Stomach big, with a deep pointed expansion basally at the point of entry of the oesophagus. Foot big, with a pair of characteristic adhesive papillae at the tip. Measurements of twenty big living individuals from Praxillella (standard deviations in parentheses). Width I of calyx is the distance between the tips of the sensory papillae, and width II of the calyx is that measured on a level with the upper part of the stomach. Total length Width I of calyx Width II of calyx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Depth of calyx Length of foot Total length/width I of calyx Width I1width II of calyx... . . .. . Width II1depth of calyx Total lengthllength of foot
575 (35) ~I 279 (17) 11 133 (5) 11 111 (1) jL 283 (13) jL 2.04 (0.14) 2.14 (0.12) 1.19 (0.07) 2.06 (0.10)
The buds are situated antero-Iaterally on a level with the upper wall of the stomach, pointing sidewards. The big buds have a total length of about 210 and 10 tentacles. Each population contains only few individuals with buds, and in most cases each individual has only one bud; a maximum of 2 + 1 buds has been observed. The number of embryos, however, may often be up to ten. Buds all the year round; embryos in June-January. This species is very characteristic with its highly projecting sense organs, the sharp edge along the lophophore and the characteristic adhesive papillae at the tip of the foot. The Y-shaped cell row is also found in Loxosomella polita and L. similis, and an unbranched line along the back of the peduncle is described from Loxosoma davenporti Nickerson, Loxosomella crassicauda (Salensky), and L. tethyae (Salensky). Special organs for attachment on the foot are described from Loxosomella neapolitana (Kowalewsky), which has
'I
STUDIE.S ON DANISH ENTOPROCfA
19
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four such organs at the tip of the foot, and from L. mortenseni (Marcus) which has a row of these papillae all along the margin of the foot. In the present species, however, there are only two, situated at the tip of the foot.
o
A
B Fig. 10. Loxosomella elegans. A-e, expanded individuals seen in frontal view, in profile; and in posterior view respectively; D. halfway contracted individual seen from the front. with a big bud; E, much contracted individual of the attached form.
Loxosomella elegans is very common in tubes of the maldanids Praxillella praetermissa (Malmgren) and Rhodine gracilior Tauber; in the tubes of the former the individuals are in most cases free, while in the tubes of the latter species they are almost always attached to the tube. In a single instance the species was found in the tube of (1) Nic:omache lumbricalis (Fabricius). In the
20
CLAUS NIELSEN
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tubes of Praxillella the populations are generally very dense, thus in a single tube no less than 50 individuals were found in the outermost half centimetre. The Danish material is from muddy and mixed bottoms, 10-60 m (Fig. 11).
'"
I
13' ___.
.. __.__ .....~9·,
I I
!
!sa·
~
_.
..._sa
S7
'Si'
i'I+---+--~
10'
13'
Fig. 11. Localities of Loxosomella elegans . , and 1.. simllis •
Loxosomella similis sp. n. Fig. 12 Holotype: Specimen found in the tube of Nicomache trispinata Arwidsson; Bergensfjord: Grunnosen (600 16' N, 5u 13.5' E), sandy mud with stones, about 55 rn, 21-8-1962; Biological Station, Espegrend, reference No. 246-62. Deposited in the Zoological Museum, Bergen, reference number 46394.
Rather small species, total length up to about 415 fl. Peduncle very short, basally either directly attached to the substratum or terminating in a rather stout foot. Upper part of calyx distinctly flattened, lower part, however, of about the same thickness and width. Behind the lophophore a projecting rim terminating in a pair of projecting lateral sense organs on a level with the under edge of the lophophore. Lophophore big, forward-directed, with 10-11 tentacles. On the back of the calyx an indistinct Y-shaped row of slightly projecting cells, the outermost of which extend almost right out to the lateral sense
21
STUDIES ON DANISH ENTOPROCTA
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organs. Stomach big, rounded, with a deep expansion at the base at the entry of the oesophagus. In free individuals the under side of this expansion touches the pedal gland. Foot slender, with no special papillae of attachment at the tip.
200f.l
A
c
Fig. 12. Loxosomella simi/is. A, expanded individual in frontal view, with a bud; B-C, expanded individual in profile and in posterior view respectively; D, contracted individual in frontal view.
Measurements of 15 big living individuals from Bergensfjord (standard deviations in parentheses): Total length Width I of calyx . . . . . . . . . . . .. . . .. . . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . Width II of calyx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Depth of calyx . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Length of foot . . . . . . . . . . . .. . . . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . Total length/width T of calyx Width I/width II of calyx Total length/length of foot . .. .. .. .. .. .. . .. . .. .. .. . .. .. . .. .. . .. .. ..
323 165
(37)!L (24)!L 9S (14)!L 83 (7)!L 141 (13)!L
1.96 1.74 2.29
(0.13) (0.16) (0.23)
The buds are formed antero-laterally on a level with the upper side of the stomach; the largest bud had eight fully developed tentacles and distinct rudiments of another pair, its total length was 215 !L. Maximum numbers observed were 1 1 buds and two embryos. Buds: May (Danish records only). Loxosomella similis bears a rather great resemblance to the preceding species, L. elegans, and to the following species, L. polita; it is distinguishable from the former by its much smaller size, its usually somewhat lower number of tentacles, and above all by the absence of special adhesive organs on the
+
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22
CLAUS NIELSEN
tip of the foot; from L. polita it is distinguishable by its higher number of tentacles and by its projecting lateral sense organs. L. similis has been found in the tubes of Nicomache trispinata, sometimes together with Loxosoma agile; one population consisted of 16 individuals. The Danish material is from stony bottom, 30-50 m (Fig. 11). Loxosomella polita sp. n.
Fig. 13 Holotype: Specimen found in the tube of Petaloproctus tenuis var. borealis Arwidsson; 0resund: Off Odinshe] (56 006' 1'1,12032' E), sandy mud with shells, 28-29 rn, 11-10-1960: deposited in the Zoological Museum, Copenhagen.
Small species, total length up to about 420 Il. Peduncle short, normally ending basally in a slender foot, but in a few cases directly attached to the substratum, and if so, the peduncle may be just as long as the calyx. Calyx somewhat flattened, almost twice as long as wide. Lophophore medium-sized, directed forward-upward, with 6-10 tentacles, most often, however, eight. In an extended state, the aboral part of the lophophore is so highly backward inclined as to form a sharp bend on the back of the calyx. Stomach big, triangularly rounded, about as high as broad, though in a contracted state somewhat flatter.
c Fig. 13. Loxosomella polita.h--C, expanded individuals seen in frontal view with one bud, in profile and in posterior view respectively; 0, contracted individual in frontal view, with one bud.
Foot with a big gland, which almost touches the lower wall of the stomach, and which in its foremost lower part at the transition to the pedal duct contains a highly refractive ball (secretion?). On the back of the calyx there is
23
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STUDIES ON DANISH ENTOPROCTA
a Y -shaped row of slightly whitish projecting cells, whose arms almost reach the small inconspicuous sense organs situated on the sides of the calyx on a level with the lower edge of the lophophore. Measurements of twenty large, free, living individuals from Petaloproctus (standard deviations in parentheses): Total length Width of calyx Depth of calyx Length of peduncle Total length/width of calyx Width/depth of calyx Total length/length of foot
. . . . . . .
Il"
367 145 101 177 2.56 1.43 2.08
(22) Ii (14) !l (10) II (8) Ii (0.22) (0.11) (0.13)
,)'
.[, ------HSI
;'~'(t~'\' .. I ).
• 1)
-~
!II'
~~\·-v~jl:.
'~'A-
11·..... _-
-J_Vj~1'!.'
d- :\!;\.~ •
~.
l'
,.
:"!
to·
Fig. 16. Localities of Loxosomella ornata.
Loxosomella ornata occurs in the tubes of the polychaete Thelepus cincinnatus (Fabricius), where up to 85 individuals may be found in each tube; the individuals have their foot buried in a spockete between the innermost layers of the tube, in precisely the same manner as in Loxosomella marsypos; moreover, the foot is often covered by detritus, which almost completely fills the pocket. The Danish finds are from various types of bottom: stones, shells, mixed bottom; depth: 20-65 m (Fig. 16).
27
STUDIES ON DANISH ENTOPROCTA
Loxosomella marsypos Nielsen & Ryland, 1961
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Fig. 17 Small species, total length including the foot about 350!1; in an extended state the peduncle plus the foot are of about the same length as the calyx. Calyx somewhat flattened, a little longer than wide; behind the upper part of the lophophore a faintly projecting rim is sometimes found. Lophophore big, directed obliquely upwards, with 8-12 tentacles. Stomach about as high as broad, when contracted, however, much flatter. Calyx sharply marked off from the quite short peduncle, which at its base has a pair of whitish cell lumps, no doubt derived from the pedal gland; in rare cases, however, these may be entirely absent. The foot lacks pedal groove and accessory glands; it is highly variable in shape, being long and narrow when extended, but, when it is contracted, a pair of wing-shaped expansions appears on the sides near the peduncle, and in a much contracted state the foot is broadly cordate.
oo
ill)
200..
o
Fig. 17. l.oxosomella marsypos. A-B, expanded individual in frontal and posterior view respectively; C, contracted individual seen from behind, situated in its pocket in the Eunice tube; D, freehand drawing of a whole, extended foot. All after Nielsen & Ryland (1961).
Measurements (to the nearest 5 !t) of five individuals (after Nielsen & Ryland. 1961 p. 45): (1)
length of calyx
.
Width of calyx Length of peduncle + foot Maximum width of peduncle
. . .
135 It 100!-L 60!-L 85 !-L
Contracted (3) (2) 145 It 185 !-L 175 !-L 175 !-L 60!-L 70 !1 95 !-L 95 !-L
Expanded (5) 200 It 130 ~l 100!1 85 !-L 145!1 155 !1 7S!1 45 !1 (4)
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28
CLAUS NIELSEN
The buds are formed antero-Iaterally on a level with the upper part of the stomach. Maximum numbers observed: one bud, three embryos. The only Danish population bad only embryos (July). Loxosomella marsypos is found in the tubes of Eunice pennata (0. F. MUlIer), where - in the same way as L. ornata, which occurs in the tubes of Thelepus - it has its foot intruded into a small pocket between the innermost layers of the tube. Only the tip of the foot is attached to the substratum, and on contraction the animal is accordingly partially withdrawn into the pocket. The only Danish find consists of a population of eight individuals found in a tube fragment about 4 cm long; the find is from a soft bottom, depth 140 m (Fig. 19). The species has previously only been known from Bergensfjord. Loxosomella harmeri (Schultz, 1895) Fig. 18
Big species, total length up to about 1 mm. Peduncle of about the same length as the calyx or a little shorter. Calyx slightly flattened, about one and a half time as long as broad. Lophophore big, directed forward and upward, with 10-12 long tentacles. When the lophophore is contracted, some small papillae (generally 4-6) of varying shape are seen on the upper part of the calyx. Stomach big, rounded, almost as high as broad, in a contracted state somewhat flatter. When the animal is extended, the calyx passes evenly into the peduncle; but when it is contracted, the calyx and peduncle are sharply separated. In the lower part of the peduncle the half-reduced pedal gland is distinctly visible. Sometimes the animals may be almost entirely covered by a brown coating, apart from a minor opening at the lophophore. The coating is of the same kind as that described in Loxosomella nitschei and L. murmanica (see p. 34). As the individuals of this species are able to change their shape pretty much, no measurements are given. The buds develop on a level with the upper wall of the stomach; they are formed alternately on the two sides, the new buds medially to the older ones. The big buds point laterally and have a total length of about 260 It; they have 8-10 tentacles, the foot is short, and the pedal gland almost touches the under side of the stomach. Maximum numbers of 5 + 4 buds and 12 embryos were observed. Buds: all the year round; embryos: March-December. The original description of Loxosomella harmeri is based on material found on the elytra of Harmothoe rarispina (?=Lagisca extenuata (Grube» and H. imbricata (Linne) from the White Sea, while the Danish finds are from elytra, antennae, and dorsal cirri of Gattyana cirrosa (Pallas). The individual populations vary considerably in size, the largest consisting of ca. 300 individuals. In spite of the great geographical distance between these localities
29
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STUDIES ON DANISH ENTOPROCTA
-- c.n)i\--://
?
C---.~ ./ -. ( /~ ----) -- -- L ---::/ c=::::::.::---,,~ / ( '\ C---
L)--'
c::::::'.-/ /''
--...-,
",~)
!
200p
A
c
\1
\l
o
de
Fig. J8. Loxosomella harmeri. A-C, expanded individuals seen in frontal view, in profile, and in posterior view respectively; D, contracted individual seen from the front, with three buds.
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30
CLAUS NIELSEN
and the occurrence of the species on different host animals, the original description fits the Danish material exceedingly well; only the papillae are a little smaller than in Schulz's drawing. Also the section through the lower part of the peduncle with the pedal gland, figured by Cori (1930 p. 12), agrees entirely with corresponding sections of Danish individuals. The Danish finds are from soft and mixed bottom, 20-110 m (Fig. 19). Loxosomella atkinsae Bobin & Prenant, 1953 Fig. 20 Synonym: Laxosomella bouxini Bobin & Prenant, 1953 c
Big species, total length up to about 1.1 mm, in most cases, however, only about 700 fl. Length of peduncle varying from two-thirds to one and a half times the length of the calyx. Calyx distinctly flattened, generally longer than wide, but otherwise very variable in shape; thus, when contracted, the calyx may be wider than long, almost cordate, the lateral parts of the calyx bending downwards along the side of the upper portion of the peduncle. On a to"
n'
".
So
I'"
··'51
II'
Fig. 19. Localities of Loxosomella marsypos _, L. harmer; •• and L. atkinsae ....
level with the lower edge of the lophophore a pair of small, non-projecting lateral sense organs are found. Lophophore big, directed forward-upward, with 10-12 tentacles (generally 10). Stomach big, rounded, about as high as broad, but varying in shape in accordance with the degree of contraction. When the animal is extended, the calyx passes evenly into the generally rather stout peduncle, whose length varies a good deal; when the animal is contracted, however, the peduncle is distinctly marked off from the calyx. On account of this ability of changing shape no measurements can be given.
31
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STUDIES ON DANISH ENTOPROCTA
The buds develop far down on the calyx, and when the mother animal is contracted, the buds almost seem to be situated on the under side of the calyx. The buds attain a total length of up to about 170 ~l; they have eight tentacles, and point forward-downward; if stirred, they bend in along the under side of the calyx of the mother animal close to the front of the peduncle. Maximum numbers of 2 + 2 buds and one embryo were observed. Buds and embryos: May-July. Loxosomella atkinsae has been found on Phasco/ion strombi (Montagu) and on the inner side of the tubes of this animal; it is often present in a rather small number, rarely exceeding 10 individuals on each Phascolion. Sometimes it is found together with L. nitschei, from which it is distinguished by its greater number of tentacles and the exceptional position of the buds. The Danish finds are from soft and mixed bottoms. 25-40 m (Fig. 19).
~Jt~ -fA ~'~-.JU
c-.~ ~;;.:-._;
S7"~·
1/
,/
~,
~
!
--HSI
I
i~
.,..-=~ , ~l
----51
i.~~ U"
.. tl'
1)"
Fig. 34. Localities of Loxosomella discopoda •• and L. scaura •.
Stomach big, rounded, somewhat broader than high. The calyx passes more or less evenly into the stout, often somewhat flattened peduncle, which basally has a more or less foot-like posterior expansion; in the adult individuals, however, no traces of a pedal gland or a pedal groove are to be found. The buds are formed antero-Iaterally on a level with the upper surface of the stomach; they resemble the buds of L. varians, being rounded, so that the foot forms no projection; the largest bud measured 160 fl. at its widest expansion. Maximum numbers observed were 1 + 1 buds and seven embryos. Buds and embryos: June-August. Loxosomella scaura differs from all the Loxosomella species hitherto described in the shape of the peduncle; as already mentioned, the buds resemble those of L. varians, but they develop antero-laterally on the calyx, not in a single median group on the front side of the calyx as in that species. The material of the species was not in a very good condition, thus only one population could be examined alive, while all the other were fixed in alcohol, which often causes a considerable shrinkage of the animals. and hence the usual measurements cannot be given. Loxosomella scaura has been found
SlUDIES ON DANISH ENTOPROcrA
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on the setae of Nephtys paradoxa and N. incisa Malmgren in a number of up to about 50 on each worm. The Danish material is from soft and mixed bottoms, 28-126 m (Fig. 34).
200~
Fig. 35. Loxosomella scaura. A, half-expanded individual in frontal view, with two buds; B, half-expanded individual seen in profile.
Loxosomella varians sp. n. Fig. 36 Holotype: Specimen found on Nephtys ciliata (0. F. MUlier); 0resund: SV of Kullen (560 IS' N, 12024' E), mud, 24 rn, 4-10-1960; deposited in the Zoological Museum, Copenhagen.
Small to medium-sized species, total length up to about 750 \-l. Peduncle varying greatly in length, being occasionally a little longer than the calyx, but in most cases much shorter. Calyx about one and a half times as long as wide, distinctly laterally compressed; in sexually mature animals, however, the gonads may increase so much in size that the width of the calyx approaches its thickness or even exceeds it. Lophophore big, directed forward and upward, with 8 shorter or longer rather thick tentacles; sometimes populations may be met with whose individuals have only six tentacles. Opening of the atrium small. Stomach big, round. The calyx passes more or less evenly into the peduncle; often the calyx is somewhat forward inclined in relation to the peduncle. The latter is generally stout and compressed, although not always exactly in plane with the compression of the calyx. At its base the peduncle sometimes has an irregular expansion, which, however, is hardly in any way associated with the quite short foot of the buds. Owing to the great variability of the species, the measurements of five fixed individuals are given here instead of the usual average measurements:
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,/
20~1
~.,
F
200..
B
Fig. 36. Loxosomella varians. A, expanded individual seen from the front; B, expanded individual seen in profile, with two buds; C, expanded individual in posterior view; D, contracted individual seen in profile; E, small individual in frontal view, with IS buds; F (the small scale), two expanded individuals with embryos, on a gill of Nephtys.
Total length ........................ Length of calyx Width of calyx Depth of calyx ...................... Length of peduncle .0 .•.•••.•••.••• Length/width of calyx ................ Depth/width of calyx ................ Length of calyx/length of peduncle .... ••••••••••••
••
0
•••
0
0.0
•••••
•••••••••
0
•••
(I)
(2)
438 ~I 350 II 210 II 236 11 881 1 1.66 1.12 4.00
508 11 376 ~ 219 ~ 263 ~l 131 ~I 1.72 1.20 2.87
(3) 245 11 175 ~ 140~
(4) 333 II 245 ~I 131 ~ 175 ~
70~
88~
1I4~
1.54 1.23 2.50
1.87 1.33 2.80
(5) 438
~l 280~
193 ~ 210 p. 158 ~ 1.46 1.09 1.78
51
STUDIES ON DANISH ENTOPROCTA
..
7"
.
10'
""
12·
""
to·
IS"
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20 ....er lillie --~---
40.....
...-
., .'--- tOO -.-
---700·.·
___:< /.:.:_>:7_.~----
/~>~ I
_.- ...... ,.. -
~.-
-t, .' _\:" ~ '"
m
dd
-
- -
- - -
..
---+1--
57'
--Hs,
\1 ,S"I+----.,~-+-
..
..::
, C:'n. \
,"
..
12"
,,"
,s"
Fig. 37. Localities of Loxosomella varians.
Measurements of sixteen living individuals gave for the ratio depth/width of the calyx the average value of 1.14 (standard deviation 0.09). The buds are formed in a single group on the front side of the calyx on a level with the middle of the stomach, and the new buds are formed above the older ones. The big buds are about 300 fl long, nearly oval, with a very short,
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CLAUS NmLSEN
clumsy foot. Often a very large number of buds are present, i. e. up to IS, and in such cases the total volume of the buds may far exceed that of the mother animal. Of embryos, a maximum number of five was observed. Buds: January-October; embryos: January-November. In the shape of the calyx and the position of the budding zone the species resembles Loxosomella discopoda, but differs markedly from it by the absence of the big adhesive disc, by its larger number of tentacles, and by the shape of the buds, those of L. discopoda having a long slender foot. Loxosomella varians is extremely common on various Nephtyidae as e. g. Nephtys ciliata, N. caeca (Fabricius), N. hombergi Savigny, N. incisa Malmgren, N. longosetosa Orsted, N. paradoxa Malm, and Aglaophamus rubella (Michaelsen). The loxosomes are often found in a number of several hundred on the gills and the parapodia with the calyx pointing towards the groove between the notopodia and the neuropodia and in most cases, the openings of the lophophores point towards the posterior end of the worm. The rich Danish material is from soft and mixed bottoms and sand, 10-200 m (Fig. 37). Along the Swedish west coast the species does not occur at depths less than about 20 m, though its host animal is often found at much smaller depths; maybe the reason for this is the influence of the brackish water coming from the Baltic and following the Swedish west coast. The species has been mentioned once previously in the literature, the Loxosoma singulare reported from Iceland by Wesenberg-Lund (1952) having turned out to be L. varians. [Fam. URNATELLIDAEl
Fig. 38 With a small basal disc from which two or three pearlstring-shaped peduncles arise, and from whose upper segments one or several calyces may be directly formed. The individual calyces may, together with the upper thin part of the peduncle which bears them, fall off and settle elsewhere, thus establishing a new colony. The anus, the nephridia, and the genital organs open into a cloaca. The individual segments of the peduncle, which are covered by a cuticle, may function as a kind of statoblasts. This family comprises only one genus, Urnatella Leidy, 1852, with a few species, which occur exclusively in fresh water. The few finds are from localities scattered over the greater part of the globe, N. America, India, Russia, and the remaining part of Europe. Since Urnatella gracilis Leidy, 1852, has been found in Belgium (Damas, 1938), Rumania (Bacescu, 1954), and Hungary (Kolosvari & Abricossov, 1960), and U. dniestriensis Zambriborshch, 1958, in SE. Russia, it is quite possible that one day a representative of this family will be found in Denmark. The peculiarly scattered occurrence of the
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family is no doubt due to the circumstance that the >statoblastsc offer good possibilities for the species to be casually introduced into places where they do not normally occur.
Fig. 38. Urnatella gracilis. After Damas (J938). Fam. PEDICELLTNIDAE
Colony-forming Entoprocta budding from branched stolons. Calyx separated from the peduncle by a diaphragm. Within this family, two types can be derived from the primitive genus Pedicellina, which has a continuous, unspecialized peduncle musculature, viz.: 1) From a basal muscular socle arises a thin elastic peduncle, which may sometimes be provided with additional muscular joints: Barentsia (including Ascopodaria and Gynopodaria) and Coriella. 2) The whole peduncle is muscular, but the musculature is more or less oblique, and the calyx is forwardinclined, as in the Loxosomatidae, and equipped on its back with a chitinous shield or chitinous spines, which may serve to protect the individuals when they bend the front side of the calyx towards the substratum: Loxosomatoides, Chitaspis, and Myosoma. In the peculiar Pseudopedicellina mutabilis Toriumi the same colony contains individuals of the Pedicellina and the Barentsia type; this species, originally described from Japan, has recently been found in Wales (Ryland, 1961a), and it may perhaps be found in Danish waters, also. From Danish waters only two genera are known, viz. Pedicellina and Barentsia, which can be distinguished from one another by the following key: 1. Musculature of peduncle continuous Pedicellina - A thin elastic peduncle, which may be provided with additional muscular joints, arises from a basal muscular socle Barentsia
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Pedicellina M. Sars, 1835 Musculature of peduncle continuous, unspecialized. It is very difficult to distinguish between the below-mentioned two North European species, and many of the finds of Pedicellina nutans reported in the literature should no doubt be referred to P. eernua. Key tot h eSc a n II ina v ian s p e c j e s
0
f P e die e II i
II
a.
Page
1. Calyx big in proportion to the thickness of the peduncle, asymmetric in profile,
the anal side being much more arched than the oral side; peduncle almost cylindrical, often with a small bulge at the top P. cernua - Calyx small in proportion to the thickness of the peduncle: almost symmetrical in profile; peduncle distinctly pointed at the top [P. nutalls]
54 56
Fig. 39. Pedicellina cernua.
Pedicellina cernua (Pallas, 1774) Fig. 39
Large species, total length of the single individuals up to about 5 nun. Calyx somewhat compressed, asymmetrical in profile, the anal side being much more arched than the oral side. Lophophore big, with 8-24 tentacles. Peduncle cylindrical or slightly tapering upwards, rounded at the top, often with a small bulge; its thickness about one-sixth of the calyx. Stolons highly ramifying, about 50 fl thick, regularly divided by partitions. The single individuals are orientated in such a way that the oral side of the calyx faces towards the budding zone of the stolon. Three forms are distinguishable, which have previously been treated as separate species: f. glabra entirely without spines, f. typica with spines on the peduncle, and f. echinata with spines on both the peduncle and the calyx; the former two have been found in Denmark. Pedicelllna cernua, which is widely distributed in the Arctic, North Atlantic, and Mediterranean regions, is well known from Danish waters and has often been mentioned in the literature. It extends right into the western Baltic,
55
STUDIES ON DANISH ENTOPROCTA
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Fig. 40. Localities of Pedicellina cernua •
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= literature
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but curiously enough it has not been found in the Sound apart from the find reported by Orsted (1844) from the northernmost part of the Sound. As it can hardly have been overlooked, its absence from the deeper parts of the Sound is quite mysterious. Its distribution otherwise seems to show that neither salinity nor temperature can be the decisive factor, and pollution can hardly come into
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CLAUS NIELSEN
question either, for the richest Danish finds are from harbours. The Danish specimens were collected from stones, algae, sponges, hydroids, bryozoans, polychaetes, crustaceans, mussels, and ascidians, from depths of 0-50 m (Fig. 40).
[Pedicellina nutans DalyeU, 1848] This species, which differs from the preceding one by its tapering peduncle and by its small, in profile symmetrical, calyx, has not yet been found in Danish waters, but is recorded by Mobius (1893) from the coast of Schleswig. Judging by its further distribution, it seems to be associated with the coasts of the Atlantic.
Barentsia Hincks, 1880 From a basal muscular socle arises a thin elastic peduncle, which may be provided with additional muscular joints. The systematics within this group has not yet been clarified, so it is necessary for the present to treat all species with this type of peduncle under the name of Barentsia. Key to the Danillh species of Barentsia I. Above the muscular socle of the peduncle follows a thin elastic portion, which passes evenly into a slightly thicker densely ringed muscular portion .. B. laxa - The muscular socle of the peduncle is succeeded upwards by an elastic portion only, or by alternating elastic and muscular portions, which do not pass evenly into one another B. gracilis
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Barentsia gracilis (M. Sars, 1835) Fig. 41 Large species, total length of the single individuals up to about 5 rom. Calyx faintly compressed, up to about 350 It long. Lophophore big, with 12-15 tentacles. Peduncle consisting of long thin, elastic segments alternating with short, thick, muscular ones. The smaller individuals have only a basal muscular segment and an elastic segment, while the big individuals may have up to 5 muscular segments. Stolons very thin; their ramifications are connected with the basal muscular segments. This cosmopolitan species is widely distributed in Danish waters except in the eastern parts of the Baltic, and has frequently been mentioned in the literature. It is found on both animate and inanimate substrata, just like Pedicellina cernua; in the Sound it is often found on the ventral side of Aphrodita aculeata and on the upper surface of elytra of Lepidonotus squamatus Linne. The Danish finds are derived from depths between 12 and 50 m (Fig. 43). The species is found both in the Kola Fjord, the Red Sea, and the Ganges delta, so it must be characterized as both eurythermal and euryhaline.
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Barentsia taxa Kirkpatrick, 1890 Fig. 42 B. laxa differs from the preceding species in the construction of the peduncle; the muscular socle is followed upwards by a thin brown elastic portion, which passes evenly into a somewhat thicker light-coloured, densely ringed portion, which is flexible and sometimes spirally coiled. No true muscular segments were observed on the peduncle in my material but in rare cases Rogick (1948) observed such a segment in her material from Woods Hole. The calyx is quite diminutive in proportion to the thickness of the peduncle. The total length of the single individuals in the Scandinavian materials is up to about 4mm.
lmm
··r
B
~ Fig. 41. (left) Barentsia gracilis. After 'Cori (1930) (redrawn). Fig. 42. (right) Barentsia taxa. A, big individual showing the characteristic spiral coiling of the upper part of the peduncle; B*, two half contracted individuals. A after Rogick (1948) (redrawn).
The Scandinavian finds of Barentsia taxa are from depths ranging from o to 200 m. The southernmost two finds (Anholt and Lese) were collected from harbour piers, where the species was found on algae, often among
58
CLAUS NIELSEN
u·
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Fig. 43. Localities of Barentsia gracilis • (0 small map) &
=
literature references) and B. laxa (the
Bryozoa, Polychaeta, Spongia, etc.; if irritated, the upper part of the peduncle will become spirally coiled, and if the irritated individual is found among polychaete tubes or similar objects, this contraction will cause the calyx to withdraw entirely into these coatings. The remaining finds are in two cases
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from Dentalium shells with Phascolion strombi, and in another case from Palliolum vitreum (Gmelin), sabellid tubes, and Bryozoa. Dr. Mary D. Rogick kindly checked the correctness of the identification. The original description of this species is based on material from Torres Straits, and the species was later found by Livingstone (1927) near Australia (Queensland, Great Barrier Reef, etc.); the Siboga Expedition found it in a couple of places in the Malay archipelago (Harmer, 1915), and it is further reported from Brazil (Marcus, 1938), the Atlantic coast of the United States of America (Osburn, 1944; Rogick, 1948; and Maturo, 1957), and Japan (Toriumi, 1949, 1951). Hence, the species is cosmopolitan. (Dr. J. S. Ryland has kindly told me that he has recently found it at Naples).
5. SYSTEMATICS OF THE LOXOSOMATIDAE When Mortensen (1911) revised the systematics of this family, he employed the structure of the foot as a generic character and separated two new genera from the earlier genus Loxosoma. The three genera were characterized as follows: 1) Loxosoma: the foot is a muscular sucking disc with scattered glandular cells; 2) Loxocalyx: the buds as well as the adult individuals have a differentiated foot with pedal gland, pedal groove, and accessory glandular cells; 3) Loxosomella: the buds have a differentiated foot, which in the adult individuals is completely reduced after the fixation of the animal to the substratum by a secretion from the pedal gland; thus, an adult individual of a Loxosomella may bear a superficial resemblance to a Loxosoma, but it is attached to the substratum, while all the Loxosoma species are able to move on the substratum throughout their life. To these Bobin & Prenant (l953d) havc added one more genus Loxomespilon, which has no peduncle at all, and is attached to the substratum by a small gland on the under side of the calyx (see GruijsFaucher, 1959). Of these genera, Loxocalyx and Loxosomella are so closely related that it has caused some difficulty to place certain species as e. g. Loxosomella harmeri, which has a distinct, though non-functioning pedal gland, the animal being attached to the substratum. As, moreover, three species are described here (Loxosomella elegans, L. similis, and L. polita) which are equally commonly met with as free individuals with a differentiated foot, and as attached individuals with no trace of a pedal gland, it must be justifiable to unite these two genera under the name of Loxosomella. The budding in Loxosoma signiilcans seems to offer an explanation of the phylogenetic connections within the family Loxosomatidae (Fig. 44). The species of Loxosoma hitherto known, in which the buds are attached to the mother animal by the central part of the pedal disc, represent the most primitive type
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:-.:
".>.:: ·:I.(::.)/.:~ .
Fig. 48. Semidiagrarnmatic picture of Loxosoma pectinaricola on Pectinaria be/pica.
side past the gills (Fig. 48). This steady water current is now and then interrupted by a brief, strong, oppositely directed current, the object of which is to remove sand, etc., from the chamber. Thus, the respiratory water currents of
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the polychaete carry fresh water containing food particles past the loxosomes, which in Pectinaria belgica are precisely so situated that the opening of the lophophore points forward in the longitudinal direction of the worm, and the respiratory current accordingly intensifies the water current through the lophophore (Fig. 48). The brief, strong, backward-flowing water current may also be assumed to be of importance for the loxosomes: As always in the Entoprocta, the embryos are attached to the embryophore of the mother animal by a gelatinous stalk, and their liberation will. no doubt, chiefly take place when these currents occur; hence the larvae will be carried directly into the fresh water masses without passing the chamber of the Pectinaria, which is constantly being searched for food particles by the tentacles. One might wonder that loxosomes have not been found on Lagis koreni, but this is, no doubt, due to the circumstance that this species, unlike Peetinaria belgica and Amphictene auricoma, is annual (Hessle, 1925); thus a loxosomatid adapted to Lagls would have no host animal on which to live from the time the one-year old individuals had disappeared after spawning till the individuals of the new generation had grown large enough to offer room for the entoprocts in their tubes. 10. T ere bell ida e : As mentioned above (p. 65), the Terebellidae produce respiration water currents through their tubes, and the three species of Loxosomella which have been found in association with Terebellidae are thus situated in a food-bearing water current. To this group may also be referred Loxosomella harmeri, whose host, Gattyana cirrosa, occurs in the tubes of Amphitrite cirrata (see p. 65). b. BRYOZOA (ECTOPROCTA)
Eighteen Loxosomatidae have been found on Bryozoa, six of them on various species of the family Reteporidae. The Bryozoa are filter feeders producing a water current by means of the lateral cilia of the lophophore; this current flows, unlike that in the Entoprocta, towards the mouth and out between the tentacles, and the food particles are filtered from this water current (Atkins, 1932b). In the Reteporidae, whose colonies are lace-like and upright, the water must finally flow out through the characteristic holes in the colony; hence this form of colony should be particularly favourable for filtration of large water masses. While all the Loxosomatidae found on Broyzoa are able to filter sufficient food from the water currents of their host animals, it is interesting to note that one-third of them are associated with Reteporidae, where the water currents seem to be particular strong. c. SIPUNCULIDA
A total of twelve Loxosomatidae have been described from various species of Phaseolion and Goljingia. The various species of Goliingia live in an
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irregular system of burrows (Tetry, 1959), but their biology is on the whole rather poorly known, and it is also impossible to say anything about the biology of the Loxosomatidae associated with them. On the other hand, we know a good deal of the biology of Phascolion; it lives in empty shells of snails, Dentalium, etc., which are partially blocked by mud. As to this, Hyman (1959, p. 675) writes as follows: :tIt appears that Phascolion, in addition to the main channel for extension and retraction, maintains a secondary excretory channel through the cement mass with which it blocks the aperture of the inhabited shell or tube. In the case the sipunculoid is lodged in a shell with siphon, this subsidiary channel for the ejection of excreta is located in the siphon. The little syllid [Syllis cornu/a] occupies this excretory channel where it benefits by outgoing currents and may find food particles in the ejecta of the host. It is probable that the commensal entoprocts also take advantage of this channel, although this is not mentioned by most authors. ¢ This view seems quite probable, and during my investigations loxosomes were almost always found in this secondary channel. d. PORIFERA
Large masses of water are constantly flowing through all Porifera and the nine species of Loxosomella found on sponges, whether situated on the outer side of the sponge or in its canal system, may benefit from these water currents. This was previously observed by Marcus (1939, p. 117), who writes: :.Dentro do genero Loxocalyx ha numerosas especies que habitam esponjas (Harmer, 1915, p. 7), aproveitando-se provavelmente das particulas alimenticias trazidas pela corrente produzida pelos flagellos dos choanocytos.e It would be interesting to know where in the canal system loxosomes are present, since they may hardly be able to secure sufficient food from the water which has passed the ciliated chambers; unfortunately, however, no observations on this phenomenon are available, und during the present investigation no loxosomes whatever were found associated with sponges. e. ECHINODERMATA
Only two loxosomes are described from echinoderms: Loxosomella antedonis on pinnules of Poliometra prolixa (Sladen) and L. discopoda on Amphilepis norvegica Ljungman. The crinoids are ciliary mucus feeders, and the association between L. antedonis and its host is therefore difficult to make out, apart from the fact that the crinoid will try to attach itself in places where suitable quantities of food particles are present in the water. The relations of L. discopoda to the ophiurid, however, is more fully known. Amphilepis is assumed to live in the same way as the Amphiura species (Mortensen, 1924), and these forms live partly buried in the bottom, where they form canals lined
with mucus along their arms leading down to a chamber around the body (des
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Arts, 1911), and fresh water is constantly driven through these canals by movements of the disc (Gislen, 1924). Thus the loxosomes situated on the under side of the disc and on the arms are located in at food-carrying current. f. ASCIDIACEA
The finding of Loxosomella leptoclini on a composite ascidian indicates that the entoproct may utilise the vigorous water currents produced by the host animal. On the other hand, nothing can be learned from the occurrence of L. crassicauda on a Ciona in an aquarium. g. COELENTERATA
No comments can be made about the two species found on hydroids, except that Loxosomella nitschei was found in an aquarium. b. PTEROBRANCHIA
The biology of Cephalodiscus being poorly known, no comments can be made as to the relations of Loxosomella leptoclini to this host animal. i. MOLLUSCA
The only record of Loxosomatidae on molluscs is given by Atkins (1927) in her paper on Loxosomella phascolosomata on the small mussels Potidoma clarkiae(Clarke) and Mysella bidentata (Montagu), which live as commensals on Goljingia elongata (Keferstein), so it will probably be more correct to refer this find to the host group Sipunculida, even though Atkins states that the loxosomes are situated near the edge of the shells, where they may derive the greatest benefit from the water currents of the mussels. 7. DISCUSSION From the survey given in the preceding section, it is quite evident that the great majority, if not all, of the loxosomes must be classified as energy commensals since their food is brought within reach by currents set up by the different host animals. This statement also agrees well with the fact that nearly all loxosomes are known to be host-specific, whieh means that their larvae do not settle at random where otherwise seemingly suitable movement of the surrounding water masses occur. For these reasons, it is obvious that the distribution of the different species is highly dependent on the distribution of the host species, although other ecological factors of course play a role. Thus, it is by no means certain that a loxosome will be as widely distributed geographically as its host. For one thing, to maintain a population of a certain loxosome in a given area, its host species must be constantly present and exhibit a certain density; for the Loxosomatidae produce only few larvae, which, moreover, are of the creeping-swimming type,
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and which according to Hyman (195], p. 544) settle after a very short time. Hence their possibility for spreading must be limited, and at any rate slow. It is the considerable size of the embryos, in proportion to that of the mother animal, which limits the production of larvae, since the atrium can only contain a small number of embryos at any given time. And although Table 2 indicates that most loxosomes reproduce during most of the year - with a maximum in the autumn - the number of larvae produced per adult is still not very high. Here, however, the asexual reproduction by budding plays a significant role. There is reason to believe that each population, which may consist of as many as 400 individuals in some species, may have developed from a single settled individual by successive budding. Although the asexual reproduction itself may in certain cases be important for the spreading of the species (cf. Ryland & Austin, ]960, p. 430), it is much more important, that it considerably increases the number of individuals producing larvae, which may in tum establish new colonies. Since each population is highly dependent on the currents of its host, it will almost certainly perish upon the death of its host, and new populations must therefore be continuously established. This is no doubt the reason why no species of loxosomes have been found associated with short-lived host species. This fact also emphasizes that the loxosomes are indeed closely adapted energy commensals, each species displaying: a strong affinity to one or a few host species. Table 2. Periods of reproduction of the Danish Loxosomatidae; data from foreign regions are not included, and species found only once are omitted.
Loxosoma pectinarico/a rhodinicola significans agile Loxosomella elegans polita ornata harmeri atkinsae nitschei phascolosomata compressa glandulifera
scaura varians
J
F
M
A
M
J
J
A
S
0
N
D
be b
b
0 0 0
b
b
be be be
b be be
be b e
be
be
be
be be b b
b b
b b be
be be b be
be be be be
be be be be
be be
b
be
be
be
be be be b be be b be be be b
be
be
be
be
e
0
b
be b be 0 be be be be be b b
be be
be
be
be
be
be be be
b be be be b be be be be be be be b be b e* be be be be
e* be
be
e* be
b = buds; e = embryos; 0 = no buds or embryos; blank = no observations; *, from Franzen (1962)
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