Molluscs Flashcards
5 general mollusc characteristics
- poorly developed head
- flat, muscular foot on ventral surface
- visceral mass
- shell covers dorsal body
- mantle secreted shell
Examples of molluscs
Snails, slugs, clams, squid, octopus
General characteristics of molluscs
- habitat
- body
- mantle cavity content
- digestive system
- vascular system
- marine, freshwater and terrestrial
- head, muscular foot, visceral mass, calcareous shell secreted by mantle
- contains comb-like gills called ctenidia
- digestive tract has Buffalo cavity with toothed radula, salivary glands and digestive glands
- includes blood (respiratory pigments), heart, vessels and often a hemocoel
Characteristics of class Polyplacophora (chitons)
- body
- mantle
- shell
- head of the Chiton does not have tentacles and foot is broad and flat
- mantle is called a girdle and is thick and heavy
- shell divided into eight overlapping plates covered by the girdle
Katherina tunicata sp.
- type
- eyes?
- foot adaptions
- why shell divisions
- how does girdle help adhere to substrate
- where is mantle cavity located
- class Polyplacophora
- hundreds of eyes on plates (ocelli)
- foot is muscular for creeping around slowly or clinging tightly to irregular surfaces. Move by mucus secretions and foot contractions
- separate plates can form ball
- girdle can create suction seal Against a substrate by pushing girdle down and lifting inner margin up to create negative pressure
- between body and girdle (where gills are)
Cryptochiton stelleri
- type
- size
- shell plate locations
Class-Polyplacophora
- largest chiton
- shell plates embedded within and completely covered by girdle
Largest and most successful group of molluscs
Class Gastropoda
Class Gastropoda adaptation
Torsion: counterclockwise twisting of most of the Gastropod body (visceral mass, mantle and mantle cavity) that occurs during larval development.
-leads to asymmetry of the organs and a loss of the organs on usually the right side of the body.
3 groups of Gastropoda
Prosobranchs (aquatic primarily, single pair of tentacles on head, torsion)
Opisthobranch (marine, detorsion, reduction of loss of shell, 2 pairs of tentacles on head, visceral mass often incorporated into head foot complex creating secondarily bilateral symmetry)
Pulmonate (freshwater and land, detorsion with reduction or loss of shell, no gills, instead lungs) -slugs and snails
Busycon sp.
- type
- where is mouth
- where are gills
- function of operculum
- Class Gastropoda
- mouth located between tentacles, end of proboscis
- gills are ctenidium in mantle cavity (in front of heart)
- a protein or calcareous lid on the foot that seals the operative of shells when the animal retracts. Protects from drying up and seals from predators
Advantages of Gastropoda possessing asymmetrical spiral shells
- matches the torsion of snails body
- allows them to grow larger
Sinistral or dextral
Left and right opening of shell
Dendronotus sp.
- type
- does visceral mass appear to be distinct from head-foot complex?
- is there a shell?
- Class Gastropoda
- no, incorporated
- no shell
(Sea slug)
Argiolimax sp.
- type
- where are eyes
- is there a shell
- pneumostome function
- Class Gastropoda
- eyes are dark spots at the end of the tentacles on the head
- no shell
- breathing pore
Helix pomata
- type
- shell type
Class-Gastropoda
-thin shell
(Edible snail)
Function of Radula
Can you see radula action?
- used for feeding. Has teeth for scraping/ cutting food
- on underside, can see it coming out to rasp
Class-Bivalvia
- lifestyle
- examples
- Sessile, sedentary or burrowing
- oysters, mussels, scallops, clams
Class-Bivalvia characteristics
- head
- foot and visceral mass
- shell
- head is greatly reduced and is usually represented by two labial palps that are located on either side of the mouth
- foot and visceral mass are laterally compressed
- composed of two valves
Anodonta sp.
- type
- how are valves attached to shell
- what are the “scars” on inner surface
- advantages and disadvantages of having this shell
(Freshwater clam)
- class-bivalvia
- with umbo and hinge ligaments
- indicate position of the muscles
- protection, can’t grow large
What structural adaptations does the clam have for burrowing
Relaxes muscles to open shell, puts foot out and thrusts downward, squeezed water to bottom of foot causing it to balloon, then contracts and moves down open space
Class-Bivalvia
- are the gills used for respiration?
- radula?
- exchange cases and trap foot
- cilia on gills pull water into mantle cavity through incident siphon, move it over gills and back out through excurrent siphon
- NO!
Glochidium larva
- type
- is this larva beneficial to lifecycle
(Clam larva)
- class-bivalvia
- released from parent gills, must latch to host fish for weeks before dropping to bottom and becoming juvenile. Parasitic dependency causing extinction because less fish!
Mytilus edulis
- type
- byssal thread function
Sea mussel
- class-bivalvia
- used to anchor to substrates
Teredo navalis
-type
Class-Bivalvia
-shipworm
Class Cephalopoda
- examples
- why this name
- cuttlefish, octopus, squids
- head and foot have close association
Class Cephalopoda characteristics
- body
- shell
- circulatory system
- elongated, head well developed and closely associated with the foot. Foot has been drawn out to form arms and tentacles both may bear suckers
- internal shell but is reduced
- closed system and blood flows through a system of arteries, veins and capillaries
Nautilus sp.
- type
- significance
- class Cephalopoda
- only living cephalopod with external shell
Octopus sp.
- type
- shell?
Class Cephalopoda
-no internal shell
Sepia sp.
- type
- adaptation for swimming
- shell and buoyancy
(Cuttlefish)
- class Cephalopoda
- pair of undulating fins, shoots water from its gut to propel
- cuttlebone is porous internal shell to help control buoyancy
Loligo sp.
- type
- how have arms and tentacles been adapted for food capture
- why are eyes developed
- describe feeding habits
- why is mantle thick
(Squid)
- arms shorter (8), 2 long tentacles. Tentacles grab prey and bring it to arms. Tentacles have rotating hooks that can swivel 360°. Arms have static hooks (injure/kill), arms have suckers to hold prey.
- 2 eyes on either side of head used to see prey and capture
- mouth is in center of arms under head (jaws=beak). Rapid lashing and ensnaring of prey with suckered feeding tentacles
- holds many organs, has no “shell” so thick to protect
How has the circulatory system of squid been adapted for the active lifestyle
-3 hearts: 2 brachial hearts that lump blood through gills to be oxygenated. 1 systemic heart that takes oxygenated blood to other body systems. More energy efficient and can send out more oxygenated blood further.
What is the functional significance of the reduction of the shell in squid
Being able to move quick rather than slow and armoured
