4/4/2019 Learning Objectives • By the end of this unit, students will be able to… • Describe the main characteristics of mollusks and the Mollusca four main groups, giving examples of each. • Describe the principal characteristics of annelids, giving Annelida examples of each group. PHYLUM MOLLUSCA “Mollusks” Main classes of Mollusca Phylum Mollusca • Polyplacophora • Mollusca is a very diverse phylum • Chitons • Characteristics • Gastropoda • Soft-bodied animals • usually covered by a shell • Snails, Slugs, etc. • Ventral foot • Bivalvia • for locomotion • Mantle • Clams, Bivalves, etc. • covers visceral mass (body • Cephalopoda organs) • Squid, Octopus, etc. 1 4/4/2019 Phylum Mollusca Phylum Mollusca • Circulatory system • Most have • most have an open system rasplike radula • Sinuses for feeding • Hemocoel - “blood cavity” • Bivalves are • Cephalopods have closed circulatory system suspension feeders Trochophore Larva Class Polyplacophora (many plates) • Most marine • Includes marine mollusks have chitons free-swimming, • Shells consist of 8 ciliated overlapping plates trochophore larva • This larva is also found in the annelid worms. Class Gastropoda (stomach foot) Class Gastropoda • Largest group of mollusks • Body undergoes torsion • snails, slugs, nudibraches, and their relatives • a twisting of the visceral mass 2 4/4/2019 Class Bivalvia (shell has 2 halves) Class Bivalvia • Includes aquatic clams, scallops, oysters, mussels • Two-part shell • hinged dorsally • encloses bodies Class Bivalvia CLAM • Often sessile • Suspension (filter) feeders • often found in large groups or “beds” Digestive gland CLAM Heart CLASS CEPHALOPODA (HEAD FOOT) DORSAL Metanephridium Stomach Intestine Esophagus Posterior adductor muscle Ganglion Anus Anterior adductor muscle Excurrent siphon Mouth Incurrent siphon Palp Gill—partially Pedal cut ganglion Mantle Foot Shell Intestine Gonad VENTRAL 3 4/4/2019 Class Cephalopoda Class Cephalopoda • They are predators • Large brain • Active swimmers • Large eyes • 8 arms • Strong mouth • 2 tentacles • beak • hooks and suckers • radula Class Cephalopoda Class Cephalopoda Tentacles Internal (modified shell foot) Digestive tract Class Cephalopoda Class Cephalopoda • Octopods • Nautilus • eight arms • external shell • smart Mimic Octopus 4 4/4/2019 Class Cephalopoda Class Cephalopoda • Cuttlefish • Squid • produce • eight arms hypnotizing colors • two tentacles for predation • camouflage Class Cephalopoda • Giant Squid • Coevolution between predator and prey • Colossal Squid • better ways to catch prey evolve in predators • better ways to escape predator evolve in prey • large eyes to spot predators “Evolutionary Arms Race” Mimicry Mimicry Cryptic Coloration 5 4/4/2019 Annelids Cryptic Coloration PHYLUM ANNELIDA (SEGMENTED WORMS) PHYLUM ANNELIDA (SEGMENTED WORMS) • Conspicuously long bodies • Aquatic worms • Segmentation • Earthworms • both internally and externally • Leeches CLASSES OF ANNELIDA • Large, • Polychaeta compartmentalized coelom • Marine worms • serves as hydrostatic skeleton • Oligochaeta • Earthworms • Hirudinea • Leeches 6 4/4/2019 CLASS POLYCHAETA Setae Mouth • Marine worms with parapodia • appendages for Clitellum Suckers locomotion, gas exchange • Parapodia have many Parapodia setae • bristles or hair-like structures Anus Class Class Class Polychaeta Oligochaeta Hirudinea CLASS POLYCHAETA CLASS OLIGOCHAETA • Well-defined head with • Earthworms sense organs • unlike other annelids • Characterized by few short setae per segment • Body divided into > 100 segments • separated internally by septa EARTHWORM 7 4/4/2019 CLASS HIRUDINEA • Leeches • Characterized by absence of setae and appendages • Parasitic leeches have suckers 8 .