Mollusks and Annelids

1. Mollusks and Annelids

2. Kingdom Animalia Phylum Mollusca Gastropods, Bivalves, Cephalopods

3. 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.

4. 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.

5. 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

7. 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

8. 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

10. 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)

11. 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

12. 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

13. 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

14. 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