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Having the mantle cavity at the front allows the well-developed head to be withdrawn into the shell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
What is a Cephalopod’s body plan?
Mantle cavity opens forwards
Rapid, directed movement effected by expelling water through manoeuvrable funnel
Prey caught with arms/tentacles, chewed up by beak then radula
Gonochoristic and most are short lived (1-2 years)
90° body tilt then elongation
Describe a Cephalopod - Nautiloidae
Body is in external shell
Last segment is inhabited
Siphuncule controls gas/water balance in other chambers to control buoyancy
Poor swimmers – water expelled by funnel muscle
80-90 suckerless tentacles
Two pairs of ctenidia and kidneys
Nervous system and eyes simple
Describe the anatomy of Cephalopod - Celeoidae - Sepiida, Cuttlefish
Stomach, digestive gland, shell, salivary gland, brain, buccal mass, funnel, gonad, ink sac, fin, gill
Describe the anatomy of Cephalopod - Celeoidae - Teuthida, Squid
Stomach, digestive gland, brain, ‘pen’, buccal mass, ink sac, funnel, crop, mantle, siphon, parrot-like beak and mouth, 8 arms and 2 rows of suckers, 2 long feeding tentacles
Describe the anatomy of Cephalopod - Celeoidae - Octapoda, Octopus
Brain, digestive gland, buccal mass, crop, kidney, funnel, branchial heart (3?), salivary gland
Describe an Octopus’ brain
Large optic lobes
Vertical lobe, optic stalk, brachial lobe,
What do the bivalve gills demonstrate?
How organs that originally evolved for one function can be further adapted for use in totally different ways
Bivalve mollusks breathe through their gills. As filter feeders, bivalves gather food through their gills.
What are the classical features of the Coleoidea?
the large brain, the advanced eye structure, powerful jet propulsion, control over their own body patters and colours, multifunctional tentacles and a vascular system with veins and arteries
