Molluscs Flashcards
What type of coelom do molluscs have?
A true coelom so they are coelomates
Name the different parts of a generalised mollusc, give a brief definition of each
Foot - a musclar structure for movement/burrowing
Visceral mass - contains the organs and is covered by the mantle
Mantle - helps secretion
Mantle cavity - where the gills are found
Reduced coelom - combines with the blood system to form the haemocoel
What is the radula used for?
Feeding
Where is the radula located?
On the odontophore - this helps move the radula
Give the different parts of the radula
Radula sac
Radular teeth
Radula retractor muscle
Radula protractor muscle
What type of circulatory system do molluscs have?
Open circulatory system
How many extant classes are there of molluscs?
8
3 main ones being bivalves, cephalopods and gastropods
What are the main features of gastropods?
Largest group of molluscs
Development of the head
Can have one or two tentacles - for mechano/chemo detection
Eyes tend to be simple - for detecting light
Have a shell - acts as a shield/protective retreat (NOT ALL GASTROPODS HAVE SHELLS)
Foot produces a slime trail - can be used as signalling to other molluscs
Some gastropods show honing behaviour
Can undergo torsion
What is torsion?
Rotation of visceral mass and mantle cavity up to 180 degrees AKA mantle cavity is moved to the head area
Only found in gastropods
What are some of the hypothesised advantages of torsion?
Protection of the veliger larva - no real evidence for this
Protection of adult - no real evidence for this
Utilisation of oncoming water by gills
What are some disadvantages of torsion?
Anus is over the head
What is de-torsion? What undergoes it?
Untwisting themselves
Nudibranchs
What are the types of coiling of gastropod shells?
Planospiral (symmetrical)
Conispiral (asymmetrical) - shell tips to one side
What side to gastropods tend to coil on?
The right-hand side
Opposite coils cannot mate with each other - so members of the same species coil the same way
What are the most specalised gastropods?
Pulmonates
What type of hermaphrodite are slipper limpets? What does this mean?
Sequential hermaphrodite
Lie on top of one another with female at the front and the males at the back
When the female dies off the male next in line becomes a female
Give some features of the bivalves
Reduced head and nervous system
Have no radula for feeding
Held together by adductor muscles - when adductor muscles relax they open slightly and can feed
Water leaves through the exhalent siphon
Reduced foot
Most are filter feeders - have enlarged gills
Labial palp - for senting
Eyes are located on the mantle edge
Statocysts in burrower species
Give some examples of bivalves
Mussels
Scallops
Giant clam
Give some features of the cephalopods
Marine carnivores
Oreintation of the body is changed to other mollusca - lengthened along the dorso-ventral axis
Shell is reduced/lost EXCEPT in Nautilus and fossils
Are dioecious
Have courtship behaviour
Mantle cavity is muscularised
Have jet propulsion for movement
Tentacles and funnel are a modified foot
Have a radula - helps pull prey into mouth
Well developed nervous system - brain, cranium (made of cartilidge) and a complex eye
Can develop a neurotoxin when feeding
Muscles contract and relax to control chromatrophores
Give some features of the octopus eye
No blind spot
Lens is a fixed shape - it moves backwards and forwards towards/away from the retina
No colour vision
Can detect polarised light
Can detect shapes
What type of circulatory system do cephalopods have? Give some features
Have a closed circulatory system
Blood is housed in vessels
Accessory hearts pump blood into the gills to be oxygenated
Increased pressure which increases efficiency of blood to cells (needed due to high metabolic rate)
How do siphuncle in Nautilus effect buoyancy?
Takes up salt from seawater by active transport
Water starts flowing into siphuncle
Less water in chambers
So chambers can fill with gas and this increases buoyancy
Siphuncle secretes salt into the chambers which causes water to flow into the chambers - makes it less buoyant
What are coleoids?
Sub-class of cephalopods
Cuttlefish, squid and octopuses
