Mollusca - Biodiversity
What is the mollusca phylum
Second most diverse phylum after arthropods and cintain snails, osyters, octupuses and squids
They are mostly marine but some inhabit land as well
They are soft bodies animlas but most are protected by hard shells of calcium carbonate
How have molluscs evolved
They are all protostomes so their mouth developed from the anus and blastopore
This is formed from the formation of archenteron which is an endoderm lined digestive tract from gastrulation, then a body cavity lined with mesoderm
Blastopore opening at the archenteron to give second opening to the digestive tract wihc is the mouth
What did Molluscs evolve from
From annelids due to both have trochophore larvae and both share a very similar pattern of development
What are the mollusca Diagnostic Features
They are Protostomic
They have a foot, mantle and Visceral mass
They are Unsegmented and have a water filled mantle cavity
Some have a calcium carbonate shell
What is the shell made of in some molluscs
Made of calcium carbonate
Is 3 layered made up of an outer periostractum then the Nacre and then the mantle
What is the Radula used for in molluscs
This is used to allow the mollucs feed, this is done by using the Radula to scape up food from the floor or the environment they are in
How do Molluscs reproduce
Most molluscs have seperate sexes with gonads located in the visceral mass
However most snails are hermaphroditic so only 1 sex type so they al produce eggs that hatch into trochophore larvae.
Many marine molluscs life cycle start as a trochophore with ciliated larvae, that then undergo metamorphosis to form a adult form
This is except cephalopods that have a hacthling turn to mini adult
What are the 4 classes of Molluscs
Polyplacophora, Gastropoda, Bivalvia and Cephalopoda
What are Polyplacophora
These are chitons that are marine animals with an oval shape and shells that are divided to 8 dorsal platess
Chitons use a muscular foot to grp rocky surfaces and creep slowly over it
They use radulas to crape and ingest algae
Whar are Gastropoda
These are snails and slugs
Many have distinct heads with eyes at the tip of tentacles and use a radula to graze on alage or plant material that they move over due to the rippling movemnt of thre muscular foot
There are some predators like the cone snail that have teeth on their rafula to form posion darts and can bore holes in prey
How have Gastropods evolved
One of the few invertbrae to populate the land successfully but most of them are marine
Garden snail and slugs live on land and have adapted as in the place of gills, the lining of the mantle cavity function as a lung
What is Gastropod tension
During development gastro[ods undergo torsion where the viscerla mass is roated by 180 degrees so that the anus and mantle cavoity are above the head of the adult snail
What is the Gastropod shell
Most are protected by single spiralled shell where the animla can retreat to
Some species have lost the shell but developed chemical defences
Limpets have a flattened shell rather than conical
What is the Gastropod sub class Probosbranchia
Many primitive gastropods and are mainly marine so have gills
The mantle extened to the siphon to draw water in only and get directionla holes in the shell called abalone
What is the Gastropod subclass Opisthobranchia
These are sea hares and sea slugs, they both lacj shell so have chemcial defence mechanisms
The larvae have a shell and undergo gastrodpod torsion
There are no gills but an external gas exchange system
What is the Gastropod sub class Pumonata
These are mainly land baseed so have no gills, so have a lung like surface for gas exchange
What are BIvalia Gatropod class
These are muscles, clams ect so have 2 valves hinged shell that is a left and right shell
There is internal compression of the head and foot but the foot not for crawling
There is no head and so no radula
They are mainly marine and never land based
They have external fertilsation
The Bivalia shells
They have shells that are divided into 2 halves, the 2 parts are hinged by mid dorsal line and powerful adductor muscles close to the shell to protect the animal
What is the movement of bivalves
Sessile muscles secret strong threads that tether then to rocks and other surfaces
Clams can pull themselves into the sand or mud by using musclulae fot as anchor
Scallops can swim in short bursts to avoid predators by flapping their shells and jetting water out the mantle cavity
How do Bivalves eat
The mantle cavity contain gills used for feeding and gas exchange
Most are suspension feeders so trap fine particles in mucus
The cilia convey particles to the mouth and water flow into the mantle cavity via the siphon to bring in food and then water leave by excurrent siphon
What is are the Cephalopoda
These are fast movign free wimming all marine animals
They are predatory
Well developed sense organs and eyes and are highly intelligenht with brain and nervous system
Closed circulatory system
What is the basic cephalopoda structure
A mantle cover the visceral mass and the foot has been modified to muscular siphons and tentacle parts in some
Shell is reduced or missing in many
How do Octupus live and eat
They live on the sea floor by creep and scurry using thyeir 8 arms to search for crabs and other food
Fast movement can occcur when mantle cavity contract and fire water stream
Have a specialised radula and capture prey with extended radula and arms
How do Cephalopoda reproduce
One arm of the male is specialsied to tranfer sperm to females to fertilise eggs
They form a new arm for this each season as some will pull it off the present to the female species
The eggs then hatch into mini adulst not larvae like other molluscs
What is the Nautiloidea sub class of cephalopoda
Have external shell, but still have mini tentacles around the mouth
What is the Coleoidea sub class of Cephalopoda
Order Decapoda= Squids - 8 arms and 2 tentacles
Order Spiioidea= Cuttle Fish 8 arms and 2 tentacles
Order Octupoda= Octupuses 8 arms and 0 tentacles