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
