mollusca Flashcards
Mollusca characteristics
- Second biggest group of marine organisms
- Fossilise well
- adapted to every kind of habitat in marine systems
- Most abundant class = gastropods, bivalvia
Mollusca physical characteristics
- ventral
- dorsal
- mantle
- radula
what is the ventral in molluscs
muscular foot
- contains nervous units
- can be used for swimming, digging, holding on, or capturing prey; missing only in Caudofoveata)
what is the dorsal in molluscs
visceral mass containing internal organs
what is the mantle in molluscs
- sheet of tissue covering all or part of the body -> creates a space between it and the visceral mass (mantle cavity) - includes epidermis secreting the calcium carbonate shell
what is the radula in molluscs
- rasping organ containing a ribbon of chitin covered in rows of backwards-facing teeth with a moveable, fleshy base
- as teeth wear out, they are replaced by new rows from behind (lack in all bivalves and some gastropods)
- can be heavily modified
what type of circulatory system do molluscs have
- Open circulation (except cephalopods)
- blood travels freely in spongy sinuses which surround it
class gastropods characteristics
- All snails and slugs
- Head usually well-developed, with sensory appendages
- Large, muscular foot
- All show, to some degree, torsion – body has twisted so that the anus is now above the head
2 different types / subclasses of gastropods
- Prosobranchs
- Opisthobranchs (all have reduced shell)
Prosobranch characteristics
e.g. abalone, littorinids, whelks, heteropods
- Vast majority of marine snails (include heteropods)
- Mostly herbivorous - although some carnivores
- Important grazers e.g. macroalage - live on their food source
- Feed using radula
what are heteropods
- ancient group of pelagic snails
- Usually warm water
- Foot is a laterally flattened, ventral fin
- Shell generally reduced or absent
- Active carnivores
- Telescopic eye – may be better than a fish’s
orders within Opisthobranch
- Order Thecosomata - shelled pteropods
- Order Gymnosomata - naked pteropods
- Order Nudibranchia - sea slugs
gills usually absent - exchange gas across body surface
Order Thecosomata characteristics
- Foot modified into pair of wings to move
- Suspension feeders
- Trap food particles in mucous covered parapodia /mucous nets
- Play important ecological role – produce membrane bound faecal pellets that sink fast / export carbon to deep ocean when they die – help with ocean acidificaton
TGN
theco = thick (shelled)
Order Gymnosomata characteristics
- naked pteropod - Lack shell and mantle cavity
- Streamlined, pair of wings near head
- Hooks, teeth and adhesive tentacles (cephaloconi) or Tentacle bearing suckers (acetabula)
Order Nudibranchia characteristics
- Bilaterally symmetrical (secondary detorsion)
- Grazing carnivores
- Feed on sessile organisms e.g. corals, sponges
- Each family restricted to one type of prey
- Dorsal surface often has projections called cerata (Involved in gas exchange)