Phylum Mollusca

Question 1

What are the 3 classes in phylum Mollusca?

Answer 1

1. Class Gastropoda
2. Class Bivalve
3. Class Cephalopoda

Question 2

What species compose of Phylum Molluscas and what are some shared properties ?

Answer 2

• includes clams, snails, squids and many other species
• mostly marine species but many freshwater and terrestrial
• they are calcareous (made of calcium carbonate) shells that enclose soft bodies
• the shells are lost or reduced in many taxa like the slugs

Question 3

What are 8 characteristics of Phylum Mollusca?

Answer 3

• Mantle: thin layer of tissue that secretes the shell
• muscular ventral foot that is used for movement
• organs are contained in a visceral mass above the foot
• their mouthparts a traplike rasping organ called a radula (scrapes up food using radula)
• They have gills used for gas exchange and sometimes for feeding
• They have an open circulatory system and their blood is not in vessels
• have reduced coelom
• not segmented
• many with trochophore (larvae with cilia)

Question 4

What are some characteristics of the class gastropoda?

Answer 4

• they include snails and relatives
• they glide along using muscular contractions of large foot
• they have a single, coiled tubular shell (slugs have lost this)
• Torsion –> visceral mass twists during development so that the anal opening ends up being over their head and ends up in their mantle cavity
• many lack shells entirely and don’t have larvae (direct development)
• exchange gasses using ‘lung’ which is lining of mantle cavity
• most are grazers, and snape algae or plant using their radula
• few are predatory

Question 5

What are nudibranches?

Answer 5

• shell-less marine gastropods (sea slugs)
• some of them are cryptic and nice coloured
• they are protected by nematocysts of cnidarians because they eat cnidarians but somehow prevent nematocysts from firing so they end up storing the nematocysts in their own tissues and firing them when they feel threatened

Question 6

What consists of Class Bivalva and what are some characteristics?

Answer 6

1. includes clams, oysters, mussels and scallops
2. have two hinged shells
   - feed by filtering water through gills
   - have radula (no mouth and no head)
   - some are sessile
   - most are sedentary (can move if necessary)

Question 7

What are some ecological importance of bivalves?

Answer 7

• many marine species eaten by people like oysters and scallops
• shells are used for buttons and jewelry
• when oysters are responding to irritants in mantle the make pearls and those are sold as jewelry- some bivalves are invasive pests like the zebra mussels

Question 8

what are some characteristics of the class cephalopoda

Answer 8

• include squids, cuttlefish and octopuses
• they do not have an external shell
• they have an internal shell remnant
• they have long tentacles arranged around their mouth and the tentacles have suckers or hooks
• they are all predatory and have a biting beak with poisonous saliva
• they have a siphon: fused tube of mantle that helps them jet-propulsion to move
• they are the only mollusca with closed circulatory systems

Question 9

What are some reproductive properties of cephalopods?

Answer 9

1. they show maternal care especially the octopus
   - do not have trochophore larvae
   - they have direct developing juveniles that hatch looking like the adult
   - theres a squid called brooding squid and it is the only squid known to brood eggs and it goes deep into the water to brood the eggs because predication is less

Question 10

What are interesting facts about cephalopods?

Answer 10

1. they have excellent vision
2. show complex behaviour and communicate by colour and posture and solve problems to capture their prey
   - sometimes they are as intelligent as dogs