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

Fig , p. 412 nucleus rudimentary brain (pair of large ganglia in head) ovary pair of highly branched tubules that adjust water and solute levels in body cilia branching gut fluid filters through membrane folds testis oviduct pharynx; protrudes onto food, then retracts into the body between feedings genital pore pair of nerve cords that have lateral branchings flame cell opening at body surface

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

Fig , 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.

Fig , p. 413 A A fluke matures and mates in a human host. C Eggs hatch as ciliated larvae. D Larvae burrow into an aquatic snail and multiply asexually. Stepped Art B Fertilized eggs exit host in feces. E Fork-tailed, swimming larvae develop and leave the snail. F Larvae burrow into new human host, enter intestinal veins, and start a new cycle.

Beef Tapeworm Life Cycle

Fig , p. 413 proglottidsscolex B A human, the definitive host, eats infected, undercooked beef, which is mainly skeletal muscle. A Larvae, each with inverted scolex of future tapeworm, become encysted in intermediate host tissues (e.g., skeletal muscle). 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 , p. 413 B A human, the definitive host, eats infected, undercooked beef, which is mainly skeletal muscle. A Larvae, each with inverted scolex of future tapeworm, become encysted in intermediate host tissues (e.g., skeletal muscle). proglottidsscolex scolex attached to wall of intestine one proglottid 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 D Inside each fertilized egg, an embryonic, larval form develops. Cattle may ingest embryonated eggs or ripe proglottids, and so become intermediate hosts.

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 a, p. 414

“jaws” toothlike structures pharynx (everted) antenna palp (food handling) eyes chemical- sensing pit parapod tentacle

Fig b, p. 414

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

Fig a, p. 414 before feeding

Fig b, p. 414 after feeding

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 a, p. 415

anus nephridium dorsal blood vessel clitellum coelom intestine gizzard crop esophagus pharynx gut longitudinal muscle 2 of 5 hearts brain ventral nerve cord ventral blood vessel mouth circular muscle ventral nerve cord

Fig b, p. 415

anus clitellumhead

Animation: Earthworm body plan

How Earthworms Move

Fig , p. 415 bristles used in locomotion

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 a, p. 416

Fig b, p. 416

Fig c, p. 416

Fig d, p. 416

Gastropod Body Plan

Fig a, p. 416

anus gill excretory organ mantle cavity heart digestive gland shell stomach edge of mantle that covers organs radula foot

Fig b, p. 416

before torsion: mouth after torsion: mantle’s edge anus anus, which discharges wastes into mantle cavity

Animation: Snail body plan

Animation: Torsion in gastropods

Variations on the Gastropod Body Plan

Fig a, p. 417

Fig b, p. 417

mantleeye opening that leads to lung sensory tentacle foot

Fig c, p. 417

Bivalve Body Plan: Clam

Fig , p. 417 mouthleft mantleadductor muscle (cut) Water flows out through exhalant siphon Water flows in through inhalant siphon foot palpsleft gillshell

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 a, p. 418

Fig b, p. 418

Fig c, p. 418

Fig d, p. 418

arm beak internal shell radulamantle anus accessory heart reproductive organ tentacle siphongill heart ink sac

Fig e, 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

Fig , p. 419 ciliated lobe mouth brain with eyespots protonephridium stomach intestine anus one of two “toes”

Tardigrades

Fig a, p. 419 tardigrade’s mouth roundworm prey

Animation: Blood fluke life-cycle

Animation: Feeding leech

Animation: Marine polychaetes

Animation: Molluscan classes