Lecture 19: Mollusca

Question 1

What does Phylum mollusca refer to?

Answer 1

• snails, clams, squids, and many others
• most marine but many fresh water and terrestrial
• calcareous shell enclosing soft body

Question 2

what are the characteristics of mollusca?

Answer 2

• they have a Mantle which is a thin layer of tissue glands that secrete substances to make the shell
• muscular ventricle foot used for movement
• organs contained in a visceral mass above foot
• mouthpart is a strap-like rasping organ called a radula

Question 3

characteristics of mollusca cont…

Answer 3

• Gills for gas exchange and sometimes for feeding
• open circulatory system (no blood vessels, veins or arteries
• not clearly segmented
• many with larvae stage

Question 4

in the class gastropoda, what are their characteristics?

Answer 4

• snails and their relatives
• glide along using muscular contractions of large foot
• single, coiled, tubular shell
• many lack shel entirely
• most species are marine
• land snails and slugs exchange gases using ‘lung’ (lining of mantle cavity)
• most are grazers, scraping algae or plant matter using radula
• some are predatory

Question 5

what are nudibranchs?

Answer 5

they are shell-less marine gastropods

• many have vibrant colours
• they are protected by nematocysts (tiny harpoons filled with venom) of cnidarians
• they eat cnidarians but somehow prevent nematocysts from firing
• they store the nematocysts in their own tissues and fire them when threatened

Question 6

what is the class Bivalvia?

Answer 6

• clams, oysters, mussels, scallops
• mostly marine but many fresh water
• 2 hinged shells

Question 7

what are Bivalves?

Answer 7

• feed by filtering water through gills
• no radula
• some are sessile
• most sedentary but can move if necessary

Question 8

what is the class Cephalopoda?

Answer 8

• squids, cuttle fish, octopuses
• no external shell
• long tentacles arranged around mouth
• tentacles have suckers and hooks
• all predatory and radula is modified as biting beak
• have a siphon which is a fused tube of mantle that is used for jet propulsion by squids
• only mulluscs with closed circulatory system (they have blood vessels and arteries)

Question 9

Cephalopoda characteristics cont…

Answer 9

• squids attach eggs to substrate and use their maternal care to protect eggs until they hatch which means the mom could die b/c she is protecting the eggs 24/7 so she can’t get herself food
• do not have larvae stage
• direct developing juveniles
• excellent vision
• complex behaviour