Animal Evolution –The Invertebrates Chapter 25 Part 2

25.6 Flatworms—Simple Organ Systems

 Flatworms (phylum Platyhelminthes) have a three-layer embryo that develops into an adult with many organ systems but no coelom

 Three main classes: turbellarians, flukes (trematodes), and tapeworms (cestodes)

Turbellarians: Structure of a Free-Living Flatworm  Pharynx • Muscular tube connecting the mouth with the gut

 Nerve cords • Two lines of communication along length of body

 Ganglia • Cluster of nerve cell bodies (simple brain)

Flatworm Organ Systems

branching gut

rudimentary brain (pair of large ganglia in head)

ovary testis oviduct

pharynx; protrudes onto food, then retracts into the body between feedings

pair of nerve cords that have lateral branchings

pair of highly branched tubules that adjust water and solute levels in body flame cell

nucleus cilia fluid filters through membrane folds

genital pore

opening at body surface

Fig. 25-15, p. 412

Animation: Planarian organ systems

Parasites: Flukes and Tapeworms  In blood flukes (Schistosoma), reproduction takes place in mammals – immature stages live in intermediate hosts (snails)  A tapeworm body consists of proglottids – repeating hermaphroditic body units that bud from a region behind the scolex

Fluke Life Cycle: Schistosoma

A A fluke matures and mates in a human host.

F Larvae burrow into new human host, enter intestinal veins, and start a new cycle.

B Fertilized eggs exit host in feces.

E Fork-tailed, swimming larvae develop and leave the snail. C Eggs hatch as ciliated larvae.

D Larvae burrow into an aquatic snail and multiply asexually. Fig. 25-16, p. 413

A A fluke matures and mates in a human host.

F Larvae burrow into new human host, enter intestinal veins, and start a new cycle.

B Fertilized eggs exit host in feces.

E Fork-tailed, swimming larvae develop and leave the snail.

C Eggs hatch as ciliated larvae. D Larvae burrow into an aquatic snail and multiply asexually.

Stepped Art Fig. 25-16, p. 413

Beef Tapeworm Life Cycle

A Larvae, each with inverted scolex of future tapeworm, become encysted in intermediate host tissues (e.g., skeletal muscle). proglottids B A human, the definitive host, eats infected, undercooked beef, which is mainly skeletal muscle.

scolex

scolex attached to wall of intestine

one proglottid

D Inside each fertilized egg, an embryonic, larval form develops. Cattle may ingest embryonated eggs or ripe proglottids, and so become intermediate hosts.

C Each sexually mature proglottid has female and male organs. Ripe proglottids containing fertilized eggs leave the host in feces, which may contaminate water and vegetation. Fig. 25-17, p. 413

A Larvae, each with inverted scolex of future tapeworm, become encysted in intermediate host tissues (e.g., skeletal muscle). proglottids B A human, the definitive host, eats infected, undercooked beef, which is mainly skeletal muscle.

scolex

scolex attached to wall of intestine

one proglottid

D Inside each fertilized egg, an embryonic, larval form develops. Cattle may ingest embryonated eggs or ripe proglottids, and so become intermediate hosts.

C Each sexually mature proglottid has female and male organs. Ripe proglottids containing fertilized eggs leave the host in feces, which may contaminate water and vegetation. Stepped Art Fig. 25-17, p. 413

Animation: Tapeworm life cycle

25.7 Annelids—Segmented Worms

 Annelids (phylum Annelida) are bilateral worms with a coelom and a segmented body; typically with chaetae (chitin reinforced bristles)

 Three main groups: marine worms (polychaetes), oligochaetes (including earthworms), and leeches

Marine Polychaetes

Fig. 25-18a, p. 414

―jaws‖ toothlike structures pharynx (everted) antenna palp (food handling)

tentacle eyes chemicalsensing pit

parapod

Fig. 25-18a, p. 414

Fig. 25-18b, p. 414

Leeches – Bloodsuckers and Others  Leeches lack chaetae and have a sucker at either end

before feeding

Fig. 25-19a, p. 414

after feeding

Fig. 25-19b, p. 414

Oligochaetes  Example: earthworms • • • • • •

Exchange gases across body surfaces Have five hearts and a closed circulatory system Nephridia regulate coelomic fluid Nervous system of ganglia and nerve cords Hydrostatic skeleton Hermaphroditic

Earthworm Body Plan

Fig. 25-20a, p. 415

anus nephridium dorsal blood vessel clitellum

coelom

intestine gizzard crop esophagus pharynx gut longitudinal circular muscle muscle

ventral nerve cord

mouth 2 of 5 hearts

brain

ventral nerve cord

ventral blood vessel Fig. 25-20a, p. 415

Fig. 25-20b, p. 415

anus

clitellum

head Fig. 25-20b, p. 415

Animation: Earthworm body plan

How Earthworms Move

bristles used in locomotion

Fig. 25-21, p. 415

25.8 Mollusks—Animals With a Mantle

 Mollusks (phylum Mollusca) • • • • •

Bilaterally symmetrical with a reduced coelom Mantle covers internal organs, secretes a shell Feed using a hard radula Have a complete digestive tract Gills for respiration in aquatic species

Mollusk Diversity  Chitons • Eight overlapping plates

 Gastropods (snails, slugs) • Undergo torsion during development

 Bivalves (mussels, clams, oysters) • Hinged, two-part shell

 Cephalopods (squids, octopuses) • Large, fast and smart; closed circulatory system

Mollusk Groups

Fig. 25-22a, p. 416

Fig. 25-22b, p. 416

Fig. 25-22c, p. 416

Fig. 25-22d, p. 416

Gastropod Body Plan

Fig. 25-23a, p. 416

anus

gill

excretory organ

heart

mantle cavity

digestive gland stomach shell

edge of mantle that covers organs radula

foot Fig. 25-23a, p. 416

Fig. 25-23b, p. 416

before torsion:

mouth

mantle’s edge

after torsion:

mouth anus

anus, which discharges wastes into mantle cavity

Fig. 25-23b, p. 416

Animation: Snail body plan

Animation: Torsion in gastropods

Variations on the Gastropod Body Plan

Fig. 25-24a, p. 417

Fig. 25-24b, p. 417

mantle

foot

opening that leads to lung

eye

sensory tentacle

Fig. 25-24b, p. 417

Fig. 25-24c, p. 417

Bivalve Body Plan: Clam

mouth

left mantle

adductor muscle (cut)

adductor muscle (cut) Water flows out through exhalant siphon

Water flows in through inhalant siphon

foot

palps

left gill

shell

Fig. 25-25, p. 417

Animation: Clam body plan

25.9 Cephalopods—Fast and Brainy  Cephalopod (“head foot”) • Tentacles attached to the head are evolutionary modifications of the foot; they surround the mouth, which has a hard, horny beak

 Include the fastest (squids), biggest (giant squid), and smartest (octopuses) invertebrates • Jet propulsion, complex eyes, closed circulatory system, complex behavior

Cephalopods

Fig. 25-26a, p. 418

Fig. 25-26b, p. 418

Fig. 25-26c, p. 418

Fig. 25-26d, p. 418

arm beak radula tentacle

internal mantle shell

anus ink heart accessory reproductive sac gill heart organ siphon

Fig. 25-26d, p. 418

Fig. 25-26e, p. 418

Animation: Cuttlefish body plan

25.10 Rotifers and Tardigrades— Tiny and Tough  Rotifers (phylum Rotifera) and tardigrades (phylum Tardigrada) are tiny bilateral animals  Rotifers have a pseudocoelom, but are genetically closest to annelids and mollusks

 Tardigrades have a coelom and molt, and are probably relatives of roundworms and insects

Rotifer Body Plan

ciliated lobe

mouth brain with eyespots

protonephridium stomach

intestine

anus

one of two ―toes‖

Fig. 25-27, p. 419

Tardigrades

tardigrade’s mouth

roundworm prey

Fig. 25-28a, p. 419

Animation: Blood fluke life-cycle

Animation: Feeding leech

Animation: Marine polychaetes

Animation: Molluscan classes