MFWB_A - Feeding and Locomotion in Molluscs

generalised feeding

microphagous browser/grazer

radula

chitinous, ribbon-like, rows of teeth, on odontophore made of cartilage, constantly replaced from radula sac, some can be tipped with calcium, silica or oxide, can be flanked by alary processus to help bend it

herbivorous gastropods

majority of pulmonates, some freshwater and marine prosobranchs (limpet, periwinkle), some opisthobranchs (nudibranchs - sea slugs, sea hares), radula scrapes food off plants or substrate, rows of many small teeth

herbivorous opisthobranchs

seaweed/algae (macrophagous), ingest plant material and chloroplasts, digestive system cells phagocytose chloroplasts, continues producing sugars and carbohydrates, used by animal

carnivorous gastropods

marine prosobranchs, opisthobranchs, few pulmonates, fewer, larger teeth on radula for tearing and cutting, proboscis (contains radula) can be extended/extracted and inserted into prey, digested with digestive enzymes, can turn prey into soup with acidic secretions, toxins or smothering

carnivorous opisthobranchs

blue dragon, pelagic, eat venomous pelagic organisms e.g. Portuguese man o war, immune to nematocyst venom, can store nematocysts in cerata in cnidosacs

conidae family

cone snails, carnivorous, modified radula with harpoon-like teeth, bathed in neurotoxins to immobilise prey (polychaetes, other gastropods, small fish) , radula harpoon ejected from proboscis, engulfed by mouth

bivalve morphological groups

protobranchs, lamellibranchs, septibranchs

bivalve feeding

no radula, gills or other organs to obtain food, most suspension feeders (lamellibranchs), some deposit feeders (protobranchs)

protobranch feeding

primitive bivalves (deep water clams), selective depositi feeding, extendable palp proboscis/tentacle used as sense organ (foot can be used), palp have mucous secretions on bottom pick up sediment, passed to labial palps (sheet of ciliated tissue) for further sorting, small gills, used solely for respiration

lamellibranch feeding

gills to respire and eat so large surface, suspension/filter feeders, no palp proboscis but do have labial palps, gills have filaments with inter-filamentary spaces between for water flow, W-shape of them decreases over volume while increasing surface area, two gills (both W, V is demibranch), surface of gill is gill lamellae

cilia

lateral cilia, lateral-frontal cilia, frontal cilia

lateral cilia

create water current, aid in respiration

lateral-frontal cilia

form mesh to catch food, pass particles to frontal cilia, less role in water flow creation

frontal cilia

pass particles to food groove, food passed to labial palps then mouth

gastropod locomotion

mucous secretions and cilia, ~35% of metabolic costs, ~1-3mm/sec, larger species can use muscular contraction with hydrostatic skeleton, contraction causes liquids in haemocoelic spaces rot change shape, causing movement

columellar muscle

lie dorso-ventrally, act antagonistically on foot/head, withdrawal of foot to prevent drying out/from predators

tarsos muscle

lie longitudinally, transverse across foot, locomotion and prey capture

muscle contraction in gastropods

direct waves move in direction of locomotion, retrograde waves move opposite to direction of locomotion, ditaxic waves is two coordinated waves, can be direct or retrograde

bivalve burrowing

pedal retractor and shell adductor muscles relax, circular muscles contract (lengthen foot), further contraction forces blood into foot (terminal anchor), siphons close and water is expelled to soften substrate, anterior pedal retractor contracts, rocking dorsal side of shell, posterior pedal retractor contracts, rocking ventral side of shell downwards