L9 Molluscs

Question 1

What are they on the metazoans evolutionary line?

Answer 1

Protostomes, lophotrochozoa

Question 2

What is the shell made of?

Answer 2

CaCO3, secreted by the mantle

Question 3

What is the basic body plan of the molluscs?

Answer 3

Foot for locomotion
Visceral mass containing organs, covered by the mantle 
Gills
Radula, for scraping food
Open circulatory system 
Plastic body plan

Question 4

What is the role of cilia in the mantle cavity?

Answer 4

Generate a current for gas exchange and water removal

Question 5

What is haemolymph?

Answer 5

a fluid equivalent to blood in most invertebrates, occupying the haemocoel

Question 6

How does the haemolymph flow?

Answer 6

Oxygenated hamolymph pumped into the haemocoel, and bathes organs, drawn into afferent branchial vessels, and transferred to efferent branchial vessels

Question 7

What are the general characteristics of the gastropods?

Answer 7

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

Question 8

What are the classes in the molluscs?

Answer 8

Gastropods
Bivalves
Cephalopods

Question 9

What is torsion?

Answer 9

Rotation of the visceral mass through the mantle cavity 180 degrees, caused by the earlier growth of the retractor muscles on the right side.

Question 10

What are the hypothetical advantages of torsion?

Answer 10

Protection of veliger larva
Protection of the adult
Utilisation of oncoming water by gills

Question 11

What are the disadvantages to torsion?

Answer 11

Anus is placed over the head, different mechanisms evolved to deal with this

Question 12

How have different gastropods evolved to overcome disadvantages of torsion?

Answer 12

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

Question 13

What is evidence some gastropods have undergone detorsion?

Answer 13

Twisted torso e.g. sea slugs like the nudibranch, who shed shells at the larval stage, so are more vulnerable

Question 14

What is planospiral?

Answer 14

Ancestral condition where new whorls are added to the outside of old ones

Question 15

What is conispiral?

Answer 15

Shell condition where new whorls are added to the side of old ones

Question 16

Why did shells evolve to become conispiral, from planospiral?

Answer 16

Planospiral are symmetrical, however, meant all of the shell was on top of the animal, which made it difficult to move around

Question 17

What are the pulmonates?

Answer 17

Specialised gastropods that live on the land

No gills as respire in air, have a vascularised mantle cavity instead - a pall lung

Question 18

What happened to the partula snail?

Answer 18

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

Question 19

What are the main characteristics of the class bivalve?

Answer 19

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

Question 20

What animals are included in the cephalopods?

Answer 20

Squid, octopus

Question 21

What is the mode of life?

Answer 21

Active marine hunters - led to evolution of sophisticated features

Question 22

What are the general features of the cephalopods?

Answer 22

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

Question 23

What is the largest cephalopod?

Answer 23

15-18m long, the colossal squid

Question 24

What do cephalopods need a closed circulatory system?

Answer 24

Have a fast metabolic rate, as move around quickly as they are active predators, allows for better oxygen delivery

Question 25

What are the nautiloids?

Answer 25

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.

Question 26

What are the colleoidea?

Answer 26

Squid, cuttlefish, octopus