AD Molluscs Flashcards
Describe a mollusc’s shell
Early molluscs had a proteinaceous and chitinous cuticle
Progressively reinforced with calcium
Modern shells consist of crystals of calcite and argonite deposited within a framework of layers of protein (conchiolin)
Muscles pull the shell down to protect the head and foot when needed
Often conical or helically coiled
The contraction of which 2 muscles protracts the odontophore and radular ribbon through the mouth?
Radular protractor muscle
Odontophore protractor muscle
What part of a mollusc’s body is generally used to identify a mollusc remains from the guts of predators
Radula teeth
Describe an Aplacophora
No shell Calcerous spines Worm like <300mm Headless and no proper foot Live in marine sediments Most have a radula but no excretory organs Hermaphrodites
Describe a Polyplacophora (chitons)
8 overlapping plates Can roll into a ball Girdle of spiny cuticle <400mm Powerful foot Marine eg shores Kidneys but head poorly defined Radula 6-88 pairs of ctenidia
What are ctenidia?
Gills
Describe a Monoplacophora
Conical shell <30mm Weak foot Marine eg deep trenches Head poorly defined and no eyes/tentacles 6 pairs of kidneys Radula Detrital feeders Mantle cavity around foot 3-6 pairs of ctenidia
Describe a Scaphopoda (tusk shells)
Cylindrical shell <150mm Separate sexes Burrowing foot Marine sediments Head, no eyes but a radula Mantle cavity through body No ctenidia Ciliated contractile tentacles
Describe a bivalvia
Pair of shells
<1m
Separate sexes
Some use foot to burrow or others cemented to substrate (byssus)
Head has no eyes, no tentacles, no radula
May be tentacles around eyes or mantle
Ctenidia highly modified
Describe a gastropoda
Snail
Largest and most diverse group
Torsion
Single coiled shell with operculum (generally)
Well developed head with eyes, radula and sensory tentacles
Well developed crawling foot
May be gonochoristic or hermaphrodites
Describe gastropoda torsion
Rotation of visceral hump through 180°
Mantle cavity now faces forward
Anus discharges into mantle cavity over the head
Having the mantle cavity at the front allows the well-developed head to be withdrawn into the shell
Chemoreceptors within the mantle cavity can now monitor the water ahead, rather than behind
Describe Gastropoda - Superorder Opisthobranchia
Sea-slugs, sea-hares
Secondary gills or papillate body surface
Up to four pairs of tentacles
Most are carnivores
Includes planctonic mucus net feeders (pteropods) with ciliated wings
Describe Gastropoda - Superorder Pulmonata
Mainly terrestrial or freshwater
Mantle cavity evolved into air-breathing lung with pneumostome
Shell thinned or lost
Most are grazers of plants or fungi, some carnivores
Describe Gastropoda - Superorder Pulmonata Anatomy
Mantle cavity, heart, kidney, salivary gland, digestive gland, rectum, reproductive system, brain, foot
What is a Cephalopod?
Squid, octopus, cuttlefish