L9 Molluscs Flashcards
What are they on the metazoans evolutionary line?
Protostomes, lophotrochozoa
What is the shell made of?
CaCO3, secreted by the mantle
What is the basic body plan of the molluscs?
Foot for locomotion Visceral mass containing organs, covered by the mantle Gills Radula, for scraping food Open circulatory system Plastic body plan
What is the role of cilia in the mantle cavity?
Generate a current for gas exchange and water removal
What is haemolymph?
a fluid equivalent to blood in most invertebrates, occupying the haemocoel
How does the haemolymph flow?
Oxygenated hamolymph pumped into the haemocoel, and bathes organs, drawn into afferent branchial vessels, and transferred to efferent branchial vessels
What are the general characteristics of the gastropods?
Developement of the head Dorso-ventral elongation of the body Shell - acts as a retreat Undergo torsion 3/4 of molluscs are gastropods Marine, freshwater and terrestrial
What are the classes in the molluscs?
Gastropods
Bivalves
Cephalopods
What is torsion?
Rotation of the visceral mass through the mantle cavity 180 degrees, caused by the earlier growth of the retractor muscles on the right side.
What are the hypothetical advantages of torsion?
Protection of veliger larva
Protection of the adult
Utilisation of oncoming water by gills
What are the disadvantages to torsion?
Anus is placed over the head, different mechanisms evolved to deal with this
How have different gastropods evolved to overcome disadvantages of torsion?
Abalone - holes in shell, so water flows in one side, out the other, so waste doesn’t flow out of the shell
Keyhole limpet - draws freshwater in over gills, expelled through a hole in top of the shell
What is evidence some gastropods have undergone detorsion?
Twisted torso e.g. sea slugs like the nudibranch, who shed shells at the larval stage, so are more vulnerable
What is planospiral?
Ancestral condition where new whorls are added to the outside of old ones
What is conispiral?
Shell condition where new whorls are added to the side of old ones
Why did shells evolve to become conispiral, from planospiral?
Planospiral are symmetrical, however, meant all of the shell was on top of the animal, which made it difficult to move around
What are the pulmonates?
Specialised gastropods that live on the land
No gills as respire in air, have a vascularised mantle cavity instead - a pall lung
What happened to the partula snail?
Live on islands in the south pacific, predated on by invasive African land snail. Rosy wolf snail introduced to island as well to eat the invaders, however also ended up eating the partula
What are the main characteristics of the class bivalve?
Laterally compressed Shell divided into two halves, hinged at mid dorsal line by adductor muscles No distinct head Some have eyes and sensory tentacles Mantle cavity contains gills Mostly suspension feeders - lamellibranchs Have incurrent and excurrent siphon Mostly sedentary Most dioecious
What animals are included in the cephalopods?
Squid, octopus
What is the mode of life?
Active marine hunters - led to evolution of sophisticated features
What are the general features of the cephalopods?
Closed circulatory system
Shell reduced/lost
Well developed nervous system - cephalisation
Well developed eyes
Move through water by jet propulsion out of excurrent siphon
Foot is modified into tentacles
Have ink sack
What is the largest cephalopod?
15-18m long, the colossal squid
What do cephalopods need a closed circulatory system?
Have a fast metabolic rate, as move around quickly as they are active predators, allows for better oxygen delivery
What are the nautiloids?
Originated in the Cambrian, still around today live in chambered shell - only cephalopod with a shell.
Chambers used in buoyancy, siphuncle runs through the shell and allows control of solutes inside, which in turn controls amount of water.
What are the colleoidea?
Squid, cuttlefish, octopus
