Molluscs Flashcards
1
Q
Mollusc anatomy
A
- Foot
- Mantle
- Ctenidia
- Radula
- Shell and sclerites
- Tetraneurous nervous system
2
Q
Mollusc foot
A
- The foot is a ciliary motor organ
- It allows for gliding across soft and hard substances by means of ciliary beating and muscular undulations
- In cephalopods, the foot has been modified into arms
- In scaphopods and bivalves, the foot has been modified into a burrowing organ
3
Q
Mollusc mantle
A
- Forms a protective covering over the surface of the animal
- Secretes shells and sclerites
- The gap between the mantle and the foot is the mantle cavity, which harbours the gills and other organs such as the gonophores and anus
4
Q
Mollusc ctenidia
A
- These are respiratory structures (gills) which can also be used in feeding in bivalves
- Ciliary beating creates a water current through the lamellated structure
- Multiple gills in chitons and monoplacophorans, but usually reduced to one or two pairs in other forms
5
Q
Mollusc radula
A
- Ventrally attaches feeding organ
- Conveyor belt of teeth, continually replaced from the posterior
- Attached to a tough, proteinaceous odontophore and can be manipulated by muscles
6
Q
Mollusc digestive system
A
Style sac contains a rod shaped crystalline sac
7
Q
Mollusc shell
A
- Made of calcium carbonate in the crystalline form of aragonite or calcite
- Mineralogical ultrastructure varies and gives the shell different properties
- Consists of several shell layers - an organic periostracum and several underlying mineralised layers
- Secreted by the mantle
- Some molluscs have sclerites rather than a shell. These are small hardened pieces of exoskeleton. They grow to a finite size and replace regularly. When many are present, they form a protective covering of the animal
8
Q
Mollusc nervous system
A
- Tetraneurous: 4 longitudinal nerves through the body
- Ganglion: a structure containing a number of nerve cell bodies, linked by synapses, often forming a swelling on a nerve fibre
- Pedal ganglion
- Visceral ganglion
- Curcumoral nervering: nerve ring runs around the oesophagus
9
Q
Mollusc embryology
A
- Spiral cleavage: blastomeres spiral around pole to pole axis of the embryo - unique to molluscs and their close relatives
- Trochophore larva: small, translucent, free-swimming larva
10
Q
Chitons / Polyplacophora (mollusc group)
A
- Characterised by having 8 overlapping shell plates
- 750 species
- Numerous ctenidia in their mantle cavity
- Radula enforced with magnetite
- Mantle with sclerites arranged in zones
11
Q
Aplacophorans (mollusc group)
A
- Shell-less molluscs
- Approximately 350 species
- Mantle with minute aragonite sclerites
- Foot is reduced or absent
- Neomenimorphs prey on hydroids
- Chaetodermomorphs are infaunal (benthic animals that live in the substrate of a body of water) selective detritivores
- Many feature they lack have been secondarily lost
12
Q
Monoplacophorans (mollusc group)
A
- Thought to be extinct until 1959
- <20 modern species
- Have serial gills and a number of muscle scars, similar to chitons
13
Q
Scaphopods (mollusc group)
A
- Tusk shells
- 600 species
- Tapering, tubular shell
- Infaunal burrowers
- Selective detritivores (forams)
- Devonian appearance
14
Q
Gastropods (mollusc group)
A
- 15,000 species
- Grazers, carnivores, parasites and some suspension feeders
- Decoupled body into head-foot unit and visceral-mantle unit
- Torsion - can rotate body 90-180 degrees
- Dextrally (right) coiled shell, sometimes modified into a flattened shell or reduced/absent
- 1-2 gills
- Inhalant siphon
- Operculum
15
Q
Gastropod groups
A
- Patellogastropoda - flattened shell, secondary limpet morphology
- Vetigastropoda
- Caenogastropoda - 60% of all extant species
- Heterobranchia - pulmonates - terrestrial species with a pulmonata organ (lung)
- Heterobranchia - nudibranchs (‘naked gills’) - colourful to deter predators, can feed on cnidarians and ingest their stinging cells to use for their own protection
- Pelagic heterobranch - heterobranch which lives in the open sea
16
Q
Bivalves (mollusc group)
A
- Clams
- 8000 species
- Deposit and suspension feeders, some zooxanthellate species
- Radula has been lost
- Primitively burrowers, although some have become epifaunal (live on surface of bottom of body of water) and sessile
- Bivalves into a left and right shell, connected by a hinge
- Gills are the most important feeding organ
17
Q
3 types of bivalve gills
A
- Protobranch
- Lamellibranch
- Septibranch
18
Q
What is the bivalve palp organ?
A
Has grooves and consumes larger particles and rejects smaller ones
19
Q
Bivalve protobranch
A
Tentacles to collect particles and sends them to the palp organ
20
Q
Bivalve lamellibranch
A
Two sets of gills collect food - quite mobile
21
Q
Bivalve septibranch
A
Inhalant/exhalant siphon - opening for capturing prey
22
Q
Bivalve hinges
A
- Ligaments act as springs
- Adductor muscles keep shell closed
23
Q
Bivalve groups
A
- Protobranchia: possess taxodont hinges (hinge teeth)
- Pteriomorpha: mussels and oysters
- Heterodonta: possess a heterodont hinge - 2 or 3 wedge-shaped cardinal teeth set in the centre near the umbones, and also some elongated lateral teeth on the anterior and posterior margins. They can also be photosymbiotic with dinoflagellates - Tridacna. They can obtain over 70% of their energy from the algae and the remaining from suspension feeding. Strong pigments protect from UV damage
24
Q
Cephalopods
A
- 700 extant species
- More than 10,000 extinct species
- Nektonic predators - ancestral mode of life
- Foot modified into arms (tentacles)
- Beak - organ for chewing food
- Funnel for jet propulsion
25
Q
Coleoids (subclass of Cephalopods)
A
- Shell moved inside mantle
- Funnel is fused structure
- Colour changing chromatophores, nervously controlled so occurs very rapidly, cells containing pigment can expand and contract in their skin, changing the oxidation state of the pigment
- Big brains - surround the oesophagus
- Camera type eyes
- 10 arm pairs, 1 pair is reduced in octopods
- Ink sac - deterrence organ. Ink is made of melanin and carotenoids. Also a very efficient escape mechanism together with jet propulsion
- Lateral fins
- 1 gill pair (Nautilus has 2 pairs)
- Ammonoids are stem coleoids, not nautiloids
