L6 - Molluscs Flashcards
What is the phylum Mollusca?
Over 150,000 spp, probably many more. Snails, slugs, bivalves, octopuses, squids. 3 main body parts - Visceral mass : contains internal organs. Foot : muscular organ on the ventral surface for locomotion. Mantle : body covering the dorsal surface ; secretes a calcareous shell for body protection, but costly to produce and carry out
What is the phylum Mollusca? Feeding apparatus?
Posses a membranous belt, the radula, which carries rows of teeth and slides over an elongated cartilaginous base, the odontophore - the action is similar to how you would eat an ice cream. New teeth are continually worn away ; arranged in a series of transverse rows. Used for scraping, cutting, boring, grating and conveying.
What is the phylum Mollusca? What parts make up respiration in pulmonate molluscs?
Heart and lungs
What is the phylum Mollusca? What parts make up cephalisation in pulmonate molluscs?
Optic tentacle, eye, cephalic tentacle, cerebral ganglion, pedal ganglion, pleural ganglion.
What is the phylum Mollusca? What parts make up the eye in pulmonate molluscs?
Epidermis, iris, cornea, lens, ciliary muscles, retina, optic nerve.
What is the phylum Mollusca? What are the classes?
Aplacophora
Polyplacophora
Monoplacophora
Gastropoda
Bivalvia
Saphnopoda
Cephalopoda
What is the phylum Mollusca? What is the class Aplacophora?
~30 spp, a = without or none, plax = plate, pherein = to bear. Lack shell, mantle and foot. Strange, worm-like, marine, burrowing or creeping molluscs, most <5mm in size. Mantle is covered with calcareous scales or spicules.
What is the phylum Mollusca? What is the class Polyplacophora?
500 spp - chitons. Poly = many, plax = plate, pherein = to bear. Elliptical body wiht a shell composed of 8 overlapping plates. Range from a few mm long to >35cm. Common at lower levels on rocky shores. Can crawl when immersed with water. Clamp tightly to substrate when immersed. All similar in morphology and ecology. Slow moving, microphagus feeders, scraping algae and other small invertebrates from substrate with their radula.
What is the phylum Mollusca? What is the class Monoplacophora?
~30 spp, monos = single, plax = plax, pherein = to bear. All marine, live at depths greater than 2000m. Only a few cm’s long. 1 symmetrical shield shaped shell.
What is the phylum Mollusca? What is the class Gastropoda?
35,000 spp, slugs, snails, whelks, winkles. Gaster = belly, pod = foot. A large and important class of animals. Mostly marine, most have spiral shells. Limpets and abalones show a further advance on the spiral shell by increasing the size of the last whorl to completely cover the body as a convex plate to reduce drag and improve hydrodynamic profile.
What is the phylum Mollusca? What is the class Gastropoda? What are Nudibranchs?
Sea slugs, nudus = naked, brankhia = gills. Benthic gastropods that either have an enclosed shell, or shed during larval development. Gills are external, positioned around the anus.
What is the phylum Mollusca? What is the class Gastropoda? What are Sea butterflies?
Planktonic, some with reduced shells, some without. Swim using a paired extension of the lateral foot.
What is the phylum Mollusca? What is the class Gastropoda? What are Pulmonata?
Slugs and land snails. Adapted for gas exchange in air ; no gill present, use mantle cavity as a ‘lung’. No operculum. Desiccation minimised by reducing opening to mantle cavity to a small pore, the pneumostome. Most are herbivorous, some are serious agricultural pests. Some are carnivorous on earthworms & other slugs and snails.
What is the phylum Mollusca? What is the class Bivalvia?
20,000 bi = two, valva = valve. Clams, oysters, mussels, scallops. Aquatic and mostly sedentary ; undeveloped head, no radula present. Most are microphagus feeders, either filter or deposit feeders. Body is laterally compressed, enclosed by 2 valves which are hinged dorsally by elastic ligaments held together by either 1 or 2 adductor muscles. Muscles have ‘catch-fibre’ mechanism so no need for continual energy expenditure, valves lock together by opposing sockets and grooves, or teeth. Foot modified for digging or anchoring. Size varies from a few mm to over 1m
What is the phylum Mollusca? What is the class Scaphopoda?
350 spp, tusk shells. Burrowing marine molluscs ; shell tube shaped, open at both ends, 3-10cm’s long. No gills, gas exchange through mantle surface. Feed on microscopic interstitial organism collected by sticky tentacles called captacula ; radula used for breaking up food.
What is the phylum Mollusca? What is the class Cephalaopoda?
700 extant, 7,500 spp extinct. This class shows the greatest degree of modification and sophistication amongst the mollusc body plan. Natuiluses, squids, cuttlefish, octopods. Body elongated along dorsoventral axis ; head positioned at ventral end. Predatory, free swimming lifestyle. Foot divided into tentacles or arms positioned anteriorally around the mouth. Swim by jet propulsion. No external shell, but was common in fossils. Often coloured, can change pattern and shade using chromatophores, all have a radula, but also powerful beak-like jaws. Most have an ink sac, many are bioluminescent. Many show advanced behavioural abilities.
What is the phylum Mollusca? What is the class Cephalaopoda? Subclass Nautiloidea?
Only 1 living genus, Nautilus. Posses an external coiled shell ; no suckers on arms ; many tentacles. Like all cephalopod shells it is divided by septa into internal chambers ; only the last chamber is occupied by the animal.
What is the phylum Mollusca? What is the class Cephalaopoda? Subclass Ammonoidea?
All extinct, only known from fossils. Once very abundant ; coiled external shells similar to Nautilus.
What is the phylum Mollusca? What is the class Cephalaopoda? Subclass Coleoidea? What is the order Sepiida?
Cuttlefishes, e.g. sepia, sepiola. Eight arms, two tentacles, body short and broad, shell with septa, or greatly reduced or lost altogether. Use jet propulsion or swimming with lateral, all round fins. Feed on benthic crustaceans. Very highly developed colouration patterns, used for communication
What is the phylum Mollusca? What is the class Cephalaopoda? Subclass Coleoidea? What is the order Teuthoidea?
Squids, e.g. loligo, alloteuthis. Eight arms, two tentacles ; body long and slender. Shell presentas a flattened internal blade. Very efficient jet propulsion swimmers ; swimming fins are paired and mainly terminal.
What is the phylum Mollusca? What is the class Cephalaopoda? Subclass Coleoidea? What is the order Octopoda?
e.g. Octopus, eledone. Eight arms ; benthic, live in crevices. Feed on crustaceans, esp crabs. Toxin and enzymes injected into prey. Shell virtually absent. Swims with jet propulsion, crawls with arms.
What is the phylum Mollusca? What is the class Cephalaopoda? Subclass Coleoidea? What is the order Octopoda? What is the family Argonautidae?
The argonaut aka paper nautili, paper-thin eggcase secreted by females. No gas-filled chambers and is not a true cephalopod shell, but rather an evolutionary innovation unique to the genus. Used to maintain buoyancy and as a brood chamber.
