Lecture 9 - Molluscs Flashcards
2 facts about the group
second largest group of animals
extremely diverse
describe their larval stage
similar to annelids - trochophore larvae
visceral mass
contains organs and is surrounded by mantle which secretes a shell if they have one
where are gills located if they have them and describe gills
in the mantle cavity - gills consist in filaments with cilia causing movement over them
foot in molluscs
used for movement but can be modified in many ways - antagonistic muscle contraction in waves
circulatory system of basic molluscs
open- haemocoel (blood system +coelom)
radula
feeding device located in mouth cavity
blood vessels
have a few that open into haemocoel which is surrounded by hemolymph
there are 7 groups of molluscs but what are the main 3
gastropods
bivalves
cephalopods
what are the 4 main differences of gastropods compared to a standard mollusc
- head with sensory adaptations e.g eyes
- dorso-ventral elongation of body - normally results in coiling of shell and visceral mass
- shell
- torsion - rotation of visceral mass and mantle cavity through 180 degrees
what are the 3 advantages of torsion
- protection of larva in marine snails
- protection of adult
- utilisation of oncoming water by gills - gills moved to front of animal
disadvantage of torsion
anus over head
what is de torsion and how is it proven
- lose shells - to compensate some are brightly coloured or release toxins
- have structures of increase gas exchange
- some species still have a slightly twisted nervous system
gastropod symmetry
asymetrical (conispiral) - shifted over one side rather than shell sitting directly on top
what are the pulmonates
most specialised gastropods (land snails and slugs) - ditch gills and have a vascularised mantle cavity which they use like a lung
main features of bivalves
- laterally compressed
- hinged shell made of two parts
describe the head and foot of bivalves
- head and nervous system are reduced with no radula
- foot can be used for feeding but mainly used for anchorage
how do most bivalves feed
most are lamellibranchs - filter feeders
describe the gills of lamellibranchs
enlarged gills which they generate currents over
- gills are big because they are used for feeding and respiration
sex of bivalves
most are dioecious
how do bivalves attach to rocks
byssus threads
symbiotic relationships in bivalves
with algae for carbon source
bivalve eyes
sophisticated eyes very sensitive to light
2 facta about cephalopods
- largest invertebrates e.g. giant squid
- most sophisticated molluscs
how do cephalopods feed
marine carnivores with a v active lifestyle
2 different features of cephalopods compared to other molluscs
- orientation of body changed
- shell is reduced and lost so they evolved other adaptations for protection e.g. ink sak and chromatophores
sex of cephalopods
dioecious - separate sexes
cephalopod circulatory system
closed - blood vessels throughout the body
cephalopod foot
modified into tentacles - muscle contractions to move
cephalopod eyes
well developed - similar to mammals - convergent evolution
cephalopod hearing
cant hear well - possible adaptation against whales and dolphins that use noise to stun prey
cephalopod nervous system
well developed with great cephalisation - can learn
cephalopod heart
main heart + 2 accessory hearts - efficient oxygenation as they are active predators
describe the nautilus
first appeared in the cambrian but is still found in deep water - lives in chambered shell which act as buoyancy aids - can draw water in or remove it and replace with air - opposite affect on buoyancy
what are 3 animals in the class coleoidea and describe their shells
- cuttlefish - internal shell = buoyancy device
- squid - shell reduced to proteinaceous pen
- octopuses - shell is tiny or absent
