(2) Mollusca Flashcards
General Characteristics
- Eucelomate
- Foot - locomotion
- Mantle - pair of thin body folds
4.Radula - rasping moutpart - Open circulatory system (closed in cephalopods)
- Respiration - cutaneous, gills, vascular mantle, blood capillaries (lungs)
- Organ system level of organization
- Extracellular digestion
Head-foot
a). Head
-mouth with radula- toothed, rasping tongue
- sensory organs concentrated on the head
b). foot-locomotion
c). MOST bivalves lack a head and radula; filter feed
Visceral Mass
soft body houses organ systems
Mantle
thin fleshy sheath hanging down either side of body
-it protects
Three Layers of Shell
Outer: periostracum
Middle: prismatic
Inner: nacreous
Periostracum (outer)
resists acids, attack, camouflage
Prismatic (middle)
CaCO3 for strength
Nacreous (inner)
smooth mother-of-pearl to protect soft body
Mantle Cavity
-encloses gills or serves as lungs
-digestive, excretory, and reproductive products brought here
Open circulation
-blood oxygenated in gills and mantle
-goes to paired auricles of heart -> muscular ventricle: 3 chambers
- tissues bathed within coelom
-blood collected and pressure boosted by accessory hearts in front of each gill
Polyplacophora
Chitons
-dorsoventrally flattened; 8 overlapping protective plates on top
-clings to rocks, scrapes, algae
-90,000 species
Gastropoda
-land and sea slugs
-most diverse mollusk class
- only mollusk class with terrestrial forms
- coiled univalve shell (or absent)
Torsion (Gastropoda)
during embryonic development body is twisted 180 degrees, orientating anus anteriorly; advantage not clear
Feeding (Gastropoda)
a). Herbivorous - grazers of algae, plants
Ex. Snails
b). Suspension/filter- trap food particles in mantle mucous
Ex. Limpets
c). Scavengers - grazers of algae, plants
Ex. some snails
d). Carnivorous
Ex. Oyster drill
Respiration (Gastropoda)
- Gills- conchs, whelks
- Vascular Mantle (lung) - terrestrial snails, slugs
Bivalvia “two shells”
mussels, scallops, oysters, shipworms
a). two laterally compressed shells
b). no hear or radula
Respiration (Bivalvia)
cilia create water current -> incurrent siphon -> gills -> outcurrent siphon
Filter Feeding (Bivalvia)
- food trapped by mucous covered gills
- Cilia carry to labial -> mouth
- Shipworms rasp wood with shell, bacteria in gut provide cellulase
Locomotion (Bivalvia)
foot extended, burrows in sand, swells with blood and anchors, body pulled forward
Glochidium (Bivalvia)
specialized veliger larva, parasite disperses on fish gills, scales
Cephalopods
squids, octopus, cuttlefish, nautilus
a). Most have NO shell; a narrow internal chitin strip protects ganglia
b). foot as arms/tentacles in head region
c). jet propelled- water forced out
d). highly predatory; advanced eyes
e). advanced social communication
- chromatophores change color rapidly
f). closed circulation
Reproduction (Cephalopods)
males place spermatophore in female using arm; fertilised eggs attach to stones
