12. Mollusca Flashcards
Mollusca
Lophotrochozoan Triploblastic Coelomate Bilateral symmetry Hydrostatic skeleton in some, Shell No metamerism Sexual - Monoecious or Dioecious NO asexual Organ-system Open circulatory system - Closed in cephalopods
Habitats of mollusca
Mostly marine
- Cephalopods all marine
- Bivalves and gastropods can live in brackish or freshwater
Body structure of Mollusc
Head-foot
- Feeding, cephalic, sensory, locomotor organs
Visceral mass
- digestive, circulatory, respiratory, and reproductive organs
Head-foot
Well developed head with mouth and sensory organs. (not bivalves)
Mouth contains structure unique to molluscs - radula
Radula
Rasping protrusible, toungue-like organ found in most molluscs
Foot
Adapted for locomotion and/or attachment - Usually ventral Modifications - Bivalves: Laterally compressed - Cephalopods: Siphon(a funnel) for jet propulsion
Mentle
A sheath of skin extending dorsally from the visceral mass that wraps around each side of the body
- Protects soft parts
- Outer surface of the mantle secretes the shell
Mantle cavity
Houses respiratory organs
- gills or a lung
Mantle’s surface participates in gas exchange
Products from digestive, excretory, and reproductive systems empty into the mantle cavity
Reproduction of molluscs
Sexual reproduction only - Mostly dioecious
Most have free-swimming trochophore and veliger larval stages
Trochophore
Minute
Translucent
Circlets of cilia
Veliger
Free swimming
- Marine snails and bivalves
Develops from trochophore - Has the beginning of a foo, shell and mantle
Circulatory system
Most molluscs have open circulatory system
- Hemolymph not confined to vessels
- Not as efficient as closed system - Common in slow-moving animals
- Cephalopods have a circulatory system
Gastropoda
Molluscs - Snails, limpets slugs etc Many, but not all have shells Terrestrial or aquatic Bilaterally symmetrical - Visceral mass is asymmetrical
Adaptation in Gastropoda
All but few gastropods exhibit bilateral asymmetry
- Gill and kidney on the right side have been lost
- Water flows one way, left to right, clearing waste from the rectum
Bivalvia
Two valves
Sedentary filter feeders
No head no radula
Very little cephalization
Bivalvian sensory organs
Some bivalves have simple eyes - ocelli
Ocelli
A simple eye or eyespot in many types of invertebrates
Locomotion of bivalvians
Some are sedentary or sessile
Others can move slowly
Cephalopoda
Most complex molluscs Marine predators Highly mobile Vary in size All are predators Tentacles and arms used to capture prey - Octopus and cuttle fish have salivary gland that secrete a venom for immobilizing - Swim by jet propelling
Shell of cephalopods
Ancestral cephalopods had shell
- Squid and cuttlefish have internal shell called a pen
- No shell in octopus
Adaptations of cephalopods
Chromatophores
- Produce color changes in skin
- Associate with alarm or courtship
Ink sac
