Molluscs Flashcards
What is a coelom? And why is it important for evolution
A coelom is a fluid filled cavity that contains the animals internal organs. It was important for evolution as it helped development of blood vessel networks, a suspended alimentary canal and led to more complex body forms
What is special about the molluscan coelom?
It is reduced in size, which also led to a reduced important. It is called the pericardial cavity
Briefly name and state the use of the two main regions in molluscs
Head-Foot- Feeding, sensory and locomotion
Visceral mass - Digestive, circulatory, respiratory, reproductive
What is a radula?
A rasping, protruding tongue like organ
too many teeth (250 000)
not present in bivalves
What is the importance of the odontophore?
Movement of the radula
What is the function of a radula in molluscs?
Rasps fine particles of food from hard surfaces
Carries particles to the digestive tract like a conveyor belt
List 2 examples of foot modifications in molluscs
Snails - creeping motion
limpets, chitons - Attachment
Bivalves - Hatchet foot
Squids, octopuses - Siphon tentacles and head
Sea hares/butterflies - swimming
What is the mantle and mantle cavity?
Mantle is the sheet of skin that drapes over soft body parts
The mantle cavity is the space between the mantle and visceral mass which houses respiratory organs
Which mollusc class has a closed circulatory system?
Cephalopods
What are ctenidia in molluscs
Gills - kinda in the mantle cavity
ciliated and leaf like
very efficient, uses countercurrent
What are the 3 layers of a mollusc shell
periostracum
Prismatic layer
Nacreous layer
What are some features of the periostracum in molluscs
Outer organic layer, protects other layers and is composed of conchiolin
What are some features of the Prismatic layer in molluscs
Made of densely packed calcium carbonate prisms
What are some features of the nacreous shell layer in molluscs
Continuously secreted by and lays beside the mantle
pearls i think
Summarize mollusc class gastropoda
Largest and most diverse class
Marine, freshwater and terrestrial, Univalve shell
What is the name for the right and left handed shells
Dextral, and sinistral respectively
What are the advantages of torsion in gastropods
Allows for the head to be drawn in before the foot for protection
Helps clean water be brought in
Sensory organs are anterior to the head, improving stimuli sensitivity
What is the difference between coiling and torsion in gastropods
Coiling is spiralized
Effects different parts of the body
Coiling allows for more space, whereas torsion moves the organs
How can the radula be used for feeding?
It can be used to scrape things, tear, drill and can even evolve to be weaponzied
Are marine snails mono or di oecious
Dioecious, they fertilize externally into the water
Name 3 ways monoecious snails reproduce
Mutual sperm transfer, They choose a sex, or eggs are deposited in gelatinous strings or masses
What is the torsion larvae called in gastropods?
Veliger larve
Summarize gastropod subclass prosobranchia
Has torsion, Separate sexes, mainly marine snails
Summarize gastropod subclass opisthobranchia
Sea slugs, limited or no torsion, monoecious, little to no shell present
Summarize gastropod subclass pulmonata
Land snails, monoecious,no gills, no torsion (detorted), anatomically are more advanced
Summarize class bivalvia
Aquatic, clams, oysters, mussels and scallops
They burrow and attach to substrates, bore into wood and coral
Adapted to a sedentary filter feeding lifestyle
No head or radula, expansion of cilia-covered gills
How have gills and mantle adapted for gas exchange in bivalves
Wider surface area as they have morphed into a W shape
The visceral mass hangs down from the midline and connects to the gills
In cephalapods, what was modified into the tetacles?
The anterior margin of the foot
How does reproduction work in bivalves?
Most are dioecious but not all, typically external fertilization, some have specialized development
How was the shell modified in cephlapods?
In octopuses it is absent, squid and cuttlefish have it internally
How does jet propulsion occur in cephlapods?
Mantle muscles bring water in, and then circular muscles contract which forces the water out pushing it. Siphon muscles control direction
What are chromatophores?
Pigment cells that allow for changes in colours and patterns, each one has tiny muscles that allow for changes
Are cephalopods mono or di oecious?
Dioecious
