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Molluscs & Annelids

Molluscs & Annelids. Zoology LS2014, Donald Winslow 3 March 2008, Following Hickman, et al. , 2008 Ch. 16 (pp 332-344, 346-357) Ch. 17 (pp 363-378). Molluscs & Annelids. Protostome Spiral cleavage Mosaic development Eucoelomate Schizocoelous coelom formation

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Molluscs & Annelids

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  1. Molluscs & Annelids Zoology LS2014, Donald Winslow 3 March 2008, Following Hickman, et al., 2008 Ch. 16 (pp 332-344, 346-357) Ch. 17 (pp 363-378)

  2. Molluscs & Annelids • Protostome • Spiral cleavage • Mosaic development • Eucoelomate • Schizocoelous coelom formation • Many have trochophore larvae

  3. Phylum Mollusca • Coelom usually only around heart • Unsegmented with organ systems • Trochophore & veliger larvae in many • Gills (ctenidia) or lung • Circulatory system usually open • Variation in body size • Mantle, mantle cavity, shell, foot, head

  4. Molluscan characteristics • Radula & odontophore • Visceral mass • Surface epithelium, cilia & mucous glands • Metanephridic kidneys (drain from coelom) • Empty liquid waste into mantle cavity • Usually nerve ring & paired ganglia • Mostly dioecious

  5. Phylum Mollusca • Classes Caudofoveata & Solenogastres • Class Monoplacophora—one shell plate • Class Polyplacophora—8 shell plates • Class Scaphopoda—tusk shells • Class Gastropoda—snails & slugs • Class Bivalvia—clams, mussels, etc. • Class Cephalopoda—squid, octopus, etc.

  6. Class Gastropoda • Snails w/ coiled or uncoiled shells • Slugs w/ no shells • Pulmonate land snails & slugs • Marine nudibranchs (no shell, “sea slugs”) • Poisonous cone shells • Conchs, whelks, limpets, abalones

  7. Class Bivalvia • Clams, scallops, mussels, oysters • Zebra mussels, shipworms, giant clams

  8. Class Cephalopoda • Giant squid • Cuttlefish • Octopus • Chambered nautilus

  9. Phylum Annelida

  10. Developmental characteristics • Spiral cleavage & mosaic development • Protostome • Eucoelomate • Schizocoelous coelom formation • Segmentation (metamerism) • External rings called annuli • Few differences between segments

  11. Morphological characteristics • Bilateral symmetry • Chitinous setae (bristles) • Parapodia in Class Polychaeta • Cerebral ganglia • 2 ventral nerve cords with giant axons • Ganglia & lateral branches in each segment

  12. Specialization of annelid head • Tactile organs • Taste buds • Statocysts • Photoreceptors

  13. Annelid circulatory system • Closed • Dorsal blood vessel pumps blood • Aortic arches control blood flow • Ventral blood vessel • Respiration by skin, gills, or parapodia

  14. Digestion and excretion • Complete digestive tract • Unsegmented digestive tract • Nephridia in each segment remove waste from blood.

  15. Reproduction of annelids • Complete regeneration when injured • Monoecious or dioecious sex • Trochophore larvae in some taxa • Budding in some taxa

  16. Sections of annelid body • Prostomium (“head”) • Somites (“body”) • Pygidium (“tail”)

  17. Annelid coelom • Septa divide coelom and separate segments. • Fluid in coelom provides hydrostatic pressure for “hydrostatic skeleton”. • Epidermis secretes cuticle. • Peritoneum (visceral & parietal) • Mesenteries (dorsal & ventral)

  18. Phylum Annelida • Class Polychaeta • Mostly marine • Some tube-dwelling • Mostly dioecious (separate sexes) • Class Oligochaeta • Earthworms and other terrestrial & freshwater species • Class Hirudinida—leeches and relatives

  19. Examples of polychaetes • Nereis • Eunice viridis—Samoan palolo worm • Featherduster worms • Chaeopterus

  20. Earthworms • Mix, aerate, hydrate, & fertilize soil • React to many stimuli, learn • Hermaphroditic, testes, ovaries • Seminal vesicles, oviducts, seminal receptacles • Clitellum, fertilization in cocoon • Freshwater oligochaetes with gills

  21. Leeches • Ectoparasitic • Anterior & posterior suckers • Medicinal uses

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