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 Many have trochophore larvae

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

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

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.

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

Class Bivalvia Clams, scallops, mussels, oysters Zebra mussels, shipworms, giant clams

Class Cephalopoda Giant squid Cuttlefish Octopus Chambered nautilus

Phylum Annelida

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

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

Specialization of annelid head Tactile organs Taste buds Statocysts Photoreceptors

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

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

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

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

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)

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

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

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

Leeches Ectoparasitic Anterior & posterior suckers Medicinal uses