Phylum Mollusca Flashcards
1
Q
What is the Phylum Mollusca?
A
- Soft body
- Largest animal phylum after Arthropods (90,000 named living species)
- Snails, clams, mussels, octopuses, chitons, nudibranchs, squid, etc
- Lophotrochozoan Protostomes
- Triploblastic
- Coelomate (coelom is confined to small area around the heart)
- Bilateral symmetry
- Hydrostatic skeleton, and in some, a shell
- Complete gut
- No metamerism
- Reproduction: sexual (monoecious or dioecious), no asexual
- Organ system grade of organization
- Mostly open circulatory system (closed in cephalopods)
2
Q
What are the classes to Phylum Mollusca?
A
Class Gastropoda
Class Bivalvia (two valves)
Class Cephalopoda
3
Q
Explain Class Gastropoda
A
- Very diverse: snails, limpets, slugs, whelks, conchs, periwinkles, sea slugs, sea hares, sea butterflies
- more than 70,000 living species
- Many but not all, have shells
- Terrestrial or aquatic (only molluscs to exploit terrestrial environments)
- Bilateral symmetry (however, because of torsion, the visceral mass is asymmetrical)
4
Q
Explain Class Bivalvia
A
- Mussels, clams, scallops, oysters and shipworms
- Mostly sedimentary filter feeders (draw water through their gills by ciliary action)
- Marine and freshwater forms
- No head, no radula
- Very little cephalization (concentration of sensory and neural organs)
5
Q
Explain Class Cephalopoda
A
- Squids, octopuses, nautiluses, devilfish and cuttlefish
- Marine active predators (chiefly eat small fishes, other molluscs, crustaceans, and worms)
- Most complex molluscs
- Highly mobile
- Vary in size
2cm-18m
Giant squid - largest invertebrate known - All are predators - rapid swimmers
- Tentacles and arms capture prey by adhesive secretions or by suckers
Octopuses and cuttlefishes have salivary glands that secrete a
venom for immobilizing prey - Swim by expelling a jet of water from their mantle cavity through funnel (derived from the foot)
6
Q
Where do they live?
A
- Aquatic: mostly marine
Cephalopods are exclusively marine
Bivalves and gastropods can live in brackish or freshwater
habitats - Brackish = more salinity than freshwater, but not as much as seawater
- Terrestrial
Some gastropods are terrestrial
May have been among the first animals to leave the oceans
and become terrestrial
7
Q
What is the form and function of Mollusca?
A
- Mollusca body consists of two basic parts:
Head-foot (feeding, cephalic, sensory, locomotor organs)
Visceral mass (digestive, circulatory, respiratory and
reproductive organs) - Many molluscs have a protective shell secreted by the mantle
8
Q
Explain head-foot
A
- Well developed head with mouth and sensory organs (exception: bivalves)
- Mouth contains a structure unique to molluscs; the radula
- Radula is a rasping, protrusible, tonguelike organ found in most molluscs (with the exception of some bivalves and some gastropods)
9
Q
Explain the foot
A
- Adapted for locomotion and/or attachment
- Usually a ventral, sole-like structure
- Modifications
Laterally compressed foot (bivalves)
Funnel (siphon) for jet propulsion in cephalopods
10
Q
What is the mantle?
A
- Mantle is a sheath of skin, extending dorsally from the visceral mass, that wraps around each side of the body
Protects the soft parts
Outer surface of the mantel secretes the shell
11
Q
What is the mantle cavity?
A
- The mantle cavity houses respiratory organs (gills or a lung)
- The mantle’s own exposed surface also participates in gas exchange
- Products from the digestive, excretory and reproductive systems empty into the mantle cavity
12
Q
What is their reproduction?
A
- Sexual reproduction only (mostly dioecious)
Some gastropods are monoecious - Most pass through free swimming trochophore and veliger larval stages
13
Q
What is a trochophore?
A
minute, translucent with circlets of cilia
14
Q
What is a veliger?
A
Free-swimming larva of most marine snails, and bivalves. It develops from a trochophore and has the beginning of a foot, shell and mantle.
15
Q
What is the trochophore larvae?
A
- Molluscs and annelids have a trochophore larvae
- Trochophore larvae: a free swimming ciliated marine larva characteristic of members of the Lophotrochozoa clade
16
Q
What is the veliger larvae?
A
-
17
Q
What does the circulatory system transport?
A
Gases Nutrients Waster Hormones Heat
18
Q
What’s simple circulation?
A
- The simplest circulation is diffusion
Slow
Inefficient over long distances - Works for single celled or small organisms
19
Q
Examples of circulation by diffusion
A
- Protozoans
- Porifera
- Platyhelminthes
Large but very thin
Internal branching of digestive tract brings materials close to
all cells - Cnidaria
- Nematoda
20
Q
What are the types of circulatory systems?
A
- Closed circulatory system
- Open circulatory system
- Most molluscs have an open circulatory system
Hemolymph is not confined to vessels; it flows through vessels
in some parts of the body and into open sinuses in others
Not as efficient as a closed system and so is common in slow
moving animals - Cephalopods have a closed circulatory system
Closed system more common for active predators
21
Q
Explain closed circulatory system
A
- Blood is contained within vessels
- Vertebrates and some invertebrates
22
Q
Explain open circulatory system
A
- Blood is confined to vessels in only a portion of circuit through body
- Blood mixes with interstitial fluids in the hemocoel
- Because it is mixed with fluid, it is properly called hemolymph
- Arthropods and some molluscs
23
Q
What are the class Gastropoda adaptations to avoid fouling?
A
- All but a few living gastropods exhibit bilateral asymmetry
Because of coiling, the gill, and kidney on the right side have
been lost - The loss of the right gill also reduces the effects of fouling
Water flows one-way: in the left side, over the gill, and out the
right side, clearing waste from the rectum
24
Q
What is the class bivalvia sensory organs?
A
- Eyes but no head
Some bivalves have simple eyes - Ocelli: a simple eye or eyespot in many types of invertebrates
25
Q
What is the locomotion for the class bivalvia?
A
- Some bivalves are sedentary (mussels) or sessile (oysters)
- Others can move slowly
- A few bivalves move by clapping their valves together
26
Q
What is the form and function of the class cephalopods?
A
- Ancestral Cephalopods had shells
Only remaining shelled Cephalopods are the Nautilus species
Cuttlefish and squid have an internal shell called a pen
Octopuses have no shell
27
Q
What are the unique adaptations for the class Cephalopods?
A
- Special pigment cells: chromatophores
Produce colour changes in skin
Used as camouflage
Associated with alarm or courtship - Cephalopods (other than Nautilus) have an ink sac
- When animal is alarmed, it releases a cloud of ink through the anus to confuse an enemy
