1. Molluscs & Annelids Zoology LS2014, Donald Winslow 3 March 2008,
Following Hickman, et al., 2008
Ch. 16 (pp , )
Ch. 17 (pp )

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)

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

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

21. 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

22. Leeches
Ectoparasitic
Anterior & posterior suckers
Medicinal uses