Mollusks and Annelids

Phylum Mollusca Gastropods, Bivalves, Cephalopods Kingdom Animalia Phylum Mollusca Gastropods, Bivalves, Cephalopods

General Characteristics Trochophore – larval stage of development Two body regions Head-foot – contains the head (mouth & sensory organs) & the foot (locomotion) Visceral Mass –contains the vital organs covered by mantle which secretes CaCo3 to make the shell. Bilateral symmetry w/cephalization The use of gills to exchange gas. Nephridia are used to remove metabolic waste Two types of circulation Open circulatory- blood moves through vessels & into open spaces around body organs Closed circulatory – blood is enclosed entirely in vessels.

Class Gastropoda Gastropods – “stomach foot” Snails, abalones, conchs, slugs, nudibranchs, sea butterflies, sea hares, periwinkles, whelks, limpets, cowries, and cones Use radula-tongue like strip used to scrap food. Open circulatory system with two-chambered heart. Found in freshwater, saltwater & moist terrestrial habitats Land type use modified mantle to respire and water type use gills.

Class Bivalvia Bivalves-two halves of shells. Clams, oysters, scallops Open circulatory system Shell made of CaCO3 w/ mother of pearl inside Filter feeders that are usually sessile can move w/foot Incurrent & excurrent siphons to move water into and out of the body for respiration w/gills and for feeding Mostly separate sexes w/external fertilization Size ranges from 1mm to 1.5 m

Class Cephalopoda “Head-foot”-squid, octopus, nautilus, cuttlefish Closed Circulatory system Internal fertilization Largest brain of invertebrates Well-developed sensory organs Use of jet propulsion, ink sprays & camouflage

Class Cephalopoda Squid – 8 arms & 2 tentacles-catching prey Octopi – 8 arms Nautilus – 90 arms Largest – Giant Squid up to 60 feet long Nautilus only one w/outer shell, others have small internal shells called pens. Photo of Colin Dunlop's cuttlefish chomping on a fish

Phylum Annelida Segmented worms Bilateral symmetry w/cephalization Live in soil, freshwater, and the sea. External bristles-setae Most have well-developed organ systems (Photo G. Brändle)

Class Oligochaeta Earthworms -Live in soil & freshwater. Ingest soil as they burrow through Circular & longitudinal muscles w/100 identical segments. Hermaphroditic – internal fertilization. The clitellum aids in reproduction Respire through their skin so must stay moist. Use nephridia to excrete waste Bilateral symmetry w/cephalization

Pathways Food pathway mouth - pharynx - esophagus - crop (storage)-gizzard (grinding)-intestines-anus. The waste of earthworms is called castings. Circulatory pathway The blood travels to posterior via ventral blood vessel & returns to anterior via dorsal blood vessel w/aortic arches acting as a heart

Class Polychaeta Sandworms, fanworms, bloodworms, lug worms, plumed worms, sea mice Free-living marine predators Contain a pair of appendages called parapodia which are used for gas exchange, swimming and crawling. Have antennae and specialized mouthparts

Class Hirudinea Leeches Moist tropical areas Parasitic Powerful suckers both ends with no setae Uses anesthetic to prevent host from feeling Can swallow 5x weight in blood Cottobdella epshteini S.Utevsky, 1997