Lecture 19: Mollusca

Question 1

What does the phylum mollusca refer to?

Answer 1

• snails, clams, squids and many others
• mostly marine, but many freshwater and terrestrial
• calcareous shell enclosing soft body

Question 2

what are the characteristics of mollusca?

Answer 2

• Mantle: a thin layer of tissue that which has glands that secrete substance to make shell
• muscular ventral foot used for movement
• organs contained in a visceral mass above foot
• mouthparts is a strap-like rasping organ called a radula

Question 3

mollusca characteristics continued…

Answer 3

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

Question 4

what are the characteristics of Class Gastropoda

Answer 4

• snails and their relatives
• glide along using muscular contractions of large foot
• single, coiled, tubular shell
• many lack shells entirely
• most species are marine
• land snails and slugs exchange gases using “lung” (lining of mantle cavity)
• most are grazers, scrape algae or plants using radula
• few are predatory

Question 5

what are nudibranchs?

Answer 5

• shell-less marine gastropods (sea slugs)
• some cryptic, many vibrant colours
• protected by nematocysts of cnidarians
• eat cnidarians but somehow prevent nematocysts form firing
• stores nematocysts in own tissue
• fires nematocysts when threatened