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 pharynx; protrudes onto food, then retracts into the body between feedings rudimentary brain (pair of large ganglia in head) pair of nerve cords that have lateral branchings ovary testis oviduct genital pore pair of highly branched tubules that adjust water and solute levels in body flame cell nucleus cilia fluid filters through membrane folds 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 scolex B A human, the definitive host, eats infected, undercooked beef, which is mainly 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. 25-17, p. 413
A Larvae, each with inverted scolex of future tapeworm, become encysted in intermediate host tissues (e.g., skeletal muscle). proglottids scolex B A human, the definitive host, eats infected, undercooked beef, which is mainly 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. 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 clitellum dorsal blood vessel nephridium coelom intestine gizzardcrop esophagus pharynx gut longitudinal muscle circular muscle ventral nerve cord 2 of 5 hearts mouth 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 mantle cavity heart digestive gland radula edge of mantle that covers organs stomach shell 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 eye foot opening that leads to lung sensory tentacle Fig. 25-24b, p. 417
Fig. 25-24c, p. 417
Bivalve Body Plan: Clam
adductor muscle (cut) mouth left mantle 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 internal mantle shell tentacle siphon anus ink sac heart gill accessory heart reproductive organ 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