Flashcards in Molluscs Deck (44):
The molluscs are hugely diverse, second only to the...?
They have colonised a huge range of habitats. Give examples.
Marine, freshwater, deep ocean, thermal vents, terrestrial etc.
Are molluscs bilaterian?
Are molluscs proto or deuterostomes?
Protostomes: they fall into the lophotrochozoa
What kind of cleavage do protostomes have?
Spiral: cells turn 45 degrees counter-clockwise to each other during division
What kind of fertilisation do most molluscs have?
External, although there are exceptions.
Lophotrochozoans have characteristic larvae. What are they?
Trochophore larvae: they have ciliated organs (that they are named after) for movement. They feed on plankton.
After the trochophore stage is the veliger stage. What is a veliger larvae?
More developed: has extended tissue, lots of cilia, sensory organs and a protocomb.
What is a protocomb?
A tiny shell.
Terrestrial molluscs skip some of the larval stages of marine species. Why?
They need to develop quicker.
Describe the nervous system of a mollusc.
Cephalisation: they have a circumcentric nerve ring and 2 longitudinal nerve chords.
How do most molluscs move?
Via a ventral 'foot'
Where are all the major organs found in molluscs?
The DCVM or 'dorsal central visceral mass'.
The DCVM is covered by the a) mantle and b) mantle cavity. What do these structures do?
a) A thick dorsal cuticle that secretes the calcareous shell
b) Encloses water and thus the respiratory chamber, as well as the kidneys, gonads and single opening (mouth/anus)
Are molluscs coelomates?
What is the hemocoel?
The principle blood cavity.
What is the pigment in molluscan blood?
The immunity of molluscs is adaptive. True or false?
False: however it is very sophisticated.
What is a radula?
'A ribbon of chitinous, recurve teeth supported by the odontophore'.
Basically a tongue covered in teeth.
Do all molluscs possess radulae?
Yes, however it is modified depending on food source etc.
Do we have a good fossil record of molluscs?
Yes: their hard shells preserve well. Plus their radulae produce many trace fossils.
There are 7 major classes of mollusc. What are they?
Briefly describe a bivalve.
Have 2 'half shells' that can be used for locomotion. These shells are opened/closed by powerful muscles/ligaments.
How do bivalves feed?
The mantle cavity contains very large gills that trap food suspended in inhalant water.
How many siphons do bivalves have?
2: these are to circulate water.
Bivalves can be freshwater or marine. How do they bury into the sediment?
With a large foot.
What is unique about bivalves, what do they lack that other molluscs have?
No cephalisation, jaws or radulae.
Which is the most primitive mollusc group and when do they originate from?
The monoplacophorans originate from the Cambrian.
Briefly describe a monoplacophoran.
A single shell with 5-6 pairs of gills. They are deep-sea dwelling detritivores. They have small tentacles but look like limpets.
Which is the most successful/diversified mollusc group?
What kind of niches have gastropods exploited?
All the feeding styles: carnivores, detritivores and suspension feeders.
A range of habitats: deep ocean, desert, freshwater, montane, forests etc.
How do gastropods reproduce?
They are either hermaphroditic but DO NOT SELF-FERTILISE or can be dioecious.
What differs about the development of aquatic and terrestrial species?
Terrestrial species have direct development and skip out the larval stages of the aquatic species.
A central structure of the gastropod shell is the columella. What is that?
A central, calcareous axis.
The body of gastropods displays torsion due to their coiled shells. True or false?
Describe how torsion occurs in gastropods.
There is a 90 degree contraction on one ide of the body - this happens rapidly. The other side is slow to twist, creating disproportionate growth. This flips the nervous system of the mollusc.
How is body torsion an adaptive advantage for gastropods?
They can retract the body into the shell more quickly when threatened.
The single locomotive foot is covered by what? What does it do?
The operculum: a 'door' that closes the shell upon retraction of the body.
Briefly describe a scaphopod.
A marine burrower with its head own in the sediment and captacula (tentacles) sticking up. They have no gills but many cilia.
What is characteristic about an aplacophoran?
They have no shells but many spicules. They are worm-like with a reduced foot.
The a) solenogastres and b) caudofoveata are both species of aplacophoran. What are their feeding strategies?
All species of aplacophoran are marine.
How many shells does a polyplacophoran have?
What is another name for a polyplacophoran?