Phylum Mollusca

More species (200,000+) than any other animal phylum except Arthropoda More species (200,000+) than any other animal phylum except Arthropoda Soft body – often protected by CaCO 3 shell Unsegmented, typically bilaterally symmetrical I. Phylum Mollusca ©2004 Amanda Demopoulos

Fig BODY PLAN: Head (eyes/sensory), visceral mass (organs), muscular foot Mantle – covers visceral mass, secretes shell Radula – Ribbon of small chitin teeth used in feeding Gills (ctenidia-comb like) for gas exchange in mantle cavity

Radula – Ribbon of small chitin teeth used in feeding

I. Phylum Mollusca Exceptions to basic planExceptions to basic plan Bivalves lack radulasBivalves lack radulas Squids have internal shellsSquids have internal shells Octopuses have no shellsOctopuses have no shells Reproduction (for some gastropods and bivalves)Reproduction (for some gastropods and bivalves) 2 larval forms2 larval forms Trocophore – looks similar to annelid larvaTrocophore – looks similar to annelid larva Veliger – ciliated, wing-like, with shellVeliger – ciliated, wing-like, with shell Trocophore Veliger

A. Class Gastropoda (=stomach foot) Largest, most common, most diverse group (40K-75K sp)Largest, most common, most diverse group (40K-75K sp) Coiled mass of vital organs=visceral mass enclosed by a shellCoiled mass of vital organs=visceral mass enclosed by a shell SnailsSnails LimpetsLimpets AbalonesAbalones Nudibranchs – lose shell in larval stageNudibranchs – lose shell in larval stage Ventral creeping footVentral creeping foot DietDiet Many vegetarian (scrape algae off rocks with radula)Many vegetarian (scrape algae off rocks with radula) Some predatorySome predatory Prey on bivalves, worms, fishes, spongesPrey on bivalves, worms, fishes, sponges I.Phylum Mollusca 4 classes ©2004 Amanda Demopoulos

I. Phylum Mollusca A. Class Gastropoda –Torsion : –Torsion : during late veliger stage, twisting of visceral mass 180º, counter-clockwise, resulting in coiled shell –Operculum : leathery, trap door –*Drawing: radula slide, live lettuce slugs-order Sacoglossa, marine snails*

AbalonesSnails SnailsSnails

Nudibranchs

Laterally compressedLaterally compressed Hinged, 2-valved shell – (oysters, clams, mussels, scallops) muscles keep closed Hinged, 2-valved shell – (oysters, clams, mussels, scallops) muscles keep closed No head, no radula No head, no radula Sedentary lifestyle Sedentary lifestyle Some have muscular foot for burrowing (e.g., clams) Some have muscular foot for burrowing (e.g., clams) Gills used for suspension feeding (active) & respiration Gills used for suspension feeding (active) & respiration Water enters and leaves through siphons (incurrent and excurrent)Water enters and leaves through siphons (incurrent and excurrent) Some anchor to substrate with byssal threads (e.g., mussels) Some anchor to substrate with byssal threads (e.g., mussels) Scallops – Swim! (repeated clapping of valves) Scallops – Swim! (repeated clapping of valves)Swim *Drawing-Scallop shell, live flame scallop *Drawing-Scallop shell, live flame scallop I. Phylum Mollusca Anterior adductor muscle Posterior adductor muscle Valves Foot Mantle Giant clam B. Class Bivalvia (=2 valved)

1.Octopuses (5 cm – 9 m)– no shell; Cryptic, bite prey with beak-like jaw 2.Squid (giant ~ 1000 kg, 18 m) – Shell reduced to pen made of chitin 3.Cuttlefish – Carbonate shell=cuttlebone, aid in buoyancy 4.Nautilus – Shell with chambers (septa) filled with gas, buoyancy organ Exclusively marineExclusively marine Fast moving, highly mobile predatorsFast moving, highly mobile predators Large eyes Large eyes Shell reduced or absent Shell reduced or absent Foot modified as arms and tentacles bearing suckers Foot modified as arms and tentacles bearing suckers Siphon – Directs water released from mantle cavity Siphon – Directs water released from mantle cavity Move by jet propulsion-move in any direction Move by jet propulsion-move in any direction Ink sac for defense-distractionInk sac for defense-distraction I. Phylum Mollusca C. Class Cephalopoda (=head footed)

I.Phylum Mollusca Class Cephalopoda - Octopus and squid have beak-like jaws - Mouth is central among tentacles Octopus 8 arms, non-retractable w/ 2 rows of suckers Nautilus suckerless tentacles Squid 8 arms + 2 tentacles non-retractable w/suckers and hooks Cuttlefish 8 arms + 2 tentacles, retractable w/ suckers, no hooks **Drawing-squid and nautilus**

fin mantle funnel eye 2 –extensible tentacle stalks arm tentacle clubs

C. Class Polyplacophora (Many-plate- bearing=Chitons, 800 species) Mostly graze algae on rocky shorelinesMostly graze algae on rocky shorelines Exclusively marineExclusively marine 8 overlapping plates8 overlapping plates *drawing-chiton**drawing-chiton* D. Class Scaphopoda (=spade foot, Tusk shells) Predators on foraminifera and juvenile bivalvesPredators on foraminifera and juvenile bivalves Most common in deep water, buried in sedimentMost common in deep water, buried in sediment I. Phylum Mollusca © Charlotte M. Lloyd