Mollusca Flashcards
What types of symmetry are Mollusca?
Bilateral symmetry
What can be said about the coelom of Mollusca?
Reduced
What is the ventral body wall of a Mollusca?
Muscular foot
What is the dorsal body wall of a Mollusca?
Mantle
How is the shell formed in Mollusca? What does it consist of?
Mantle secretes the shell
2 folds of skin outgrowths of the dorsal body wall (mantle) and contains the gills in mantle cavity
What does the digestive system have of a Mollusca?
Radula = rasping organ
What is the circulatory system of Mollusca? Exception
Open system - except cephalopods where it’s closed
How is gas exchanged in Mollusca?
Through gills which are in the mantle cavity inside the mantle
Does Mollusca have kidneys?
Yes generally 1 or 2
Does Mollusca have any sensory organs?
Cephalopods have eyes
How do mulls a reproduce?
Most gonochoristic (separate sexes) but some are hermaphrodites
What are the larva in the marine species of Mollusca?
Free-swimming trochophore (spherical shapes, spinning motion and band of cilia)
Can some marine species of the Mollusca have a 2nd larva stage? What is it called?
Yes - snails and bivalves do - free-swimming called veliger
How do most marine larva pass through their trochophore stage in Mollusca? What happens after this stage (2x)?
While in protective capsule which was where the eggs were laid then emerge as veligers or skip this stage and straight as young adults
For terrestrial and freshwater gastropods, where are the eggs laid and do they have a veliger stage?
Some eggs not laid but develop within parent
No recognizable veliger stage
What happens to the veliger stage of freshwater bivalves?
Modified - glochidium larva in an arrow point not spherical
What are the 5 class of Mollusca?
1- polyplacophora 2- Gastropoda 3- Bivalvia 4- Scaphopoda 5- Cephalopoda
What are the class Polyplacophora?
Chitons
What does the shell of the class Polyplacophora contain?
7-8 plates
What and how do the class Polyplacophora eat?
Algae - scape rocks using radula
How do the class Polyplacophora stay on the rocks?
Using their foot - large suction cup
What are the class Gastropoda?
Snails and slugs
What does the class Gastropoda undergo? Explain basics
Torsion = visceral mass and nervous system twists 90-180’ during development
What does the class Gastropoda have on its foot?
Shield for columellar muscle to attach
Explain torsion of the class Gastropoda (3)
- Veliger larva develops some adult organs (shell and foot)
- Head and foot remain in place but visceral mass rotates so anus and mantle cavity end up same end as head
- organs on one side of body do not develop
What are the 2 subclasses of the class Gastropoda?
1- Opisthobranchia
2- Pulmonata
What are 3 examples of the subclass Opisthobranchia of the class Gastropoda
Sea horses
Sea slugs
Bubble shells
Where is the mantle cavity in the subclass Opisthobranchia of the class Gastropoda? Why?
Lateral or posterior due to loss or detorsion
What are the 5 trends in the subclass Opisthobranchia of the class Gastropoda?
1- reduction/loss of shell
2- reduction/loss of operculum (gill covering)
3- limited torsion
4- reduction/loss of mantle cavity
5- reduction/loss of ctenidia (alternative respiratory structures)
What is the order of the subclass Opisthobranchia of the class Gastropoda? What do they include?
Nudibranchio
Sea slugs
What happens to the shell of the order Nudibranchio of the subclass Opisthobranchia of the class Gastropoda?
Shell is discarded at adulthood
If adults of the order Nudibranchio of the subclass Opisthobranchia of the class Gastropoda lack mantle cavity and ctenidia, how does has exchange happen?
Cerata = brightly coloured extension of the digestive system
How do the order Nudibranchio of the subclass Opisthobranchia of the class Gastropoda reproduce?
Hermaphrodites
How do the order Nudibranchio of the subclass Opisthobranchia of the class Gastropoda defend themselves?
Some have chemicals others have unfired nematocysts from Cnidarian prey
What happens to the mantle cavity of the subclass Pulmanata of the class Gastropoda?
Highly vascularized and modified to form a lung
Do the subclass Pulmanata of the class Gastropoda have shells?
Most do - even slugs have theirs enclosed within their mantel
If the subclass Pulmanata of the class Gastropoda do not have ctenidia, how do their breath? (2)
Either Evolve secondary gills
Or mantle cavity acts as lung so floor of cavity draws air or water in for respiration - the inlet/outlet is pneumostome
How do the subclass Pulmanata of the class Gastropoda reproduce?
Hermaphrodites
What is the class Bivalvia? 4 examples
Pelecypoda
Clams/mussels/oysters/shipworms
What does pelecypoda mean?
2-valved shell, body is flattened laterally
How are the subclasses of the class Bivalvia defined?
By their gill structures
Explain the shell of the class Bivalvia
Hinged shell joined by ligament that opens when adductor muscles relax
What 2 things does the class Bivalvia lack?
Cephalization and radula complex
What are the 3 families and an example each for the class Bivalvia?
1- Mytilidae = mussels
2- Ostreidae = oysters
3- Pectinidae = scallops
Explain the shape of the class Scaphopoda
Tusk shaped of conical shell which opens at both ends
How does the class Scaphopoda feed?
Have anterior feeding tentacles
When did the class Scaphopoda first appear?
450 MYA
What 3 things does the class Scaphopoda lack?
Ctenidia, heart and circulatory system
What are 4 examples of the class Cephalopoda?
Squid, octopus, cuttlefish and nautilus
How many species in the class Cephalopoda? How many with shells?
600 spp but only 6 with shells = nautilus
What are the 2 Mollusca taints present in the class Cephalopoda and what 2 are modified?
Present = ctenidia and radula Modified = mantle cavity and foot
What happens to the shell in the class Cephalopoda?
Many reduced or lost
Some shell is divide by septa with chambers connected by siphuncle (tube of CaCO3)
What s the circulatory system in the class Cephalopoda?
Closed
What has happened to the foot in the class Cephalopoda?
Modified to give flexible arms and siphon or funnel
Explain the Brian in the class Cephalopoda
Ganglia (# of nerve cell bodies) fused to form large Brian in cartilaginous cranium
What has happened to the shell in nautilus of the class Cephalopoda?
Coiled in planospiral fashion = whorls lie on single plane
What does nautilus of the class Cephalopoda lack?
Periostracum - skin on outmost layer of shell
If the shell of the nautilus of the class Cephalopoda is divided by a septa, who are the chambers used?
Only the last chamber is used but the living animal = can withdraw into chamber and cover opening with hood
How does the nautilus of the class Cephalopoda grow?
With growth it moves forwards forming a new septum behind it
