Transcript Classes of Molluscs - Solon City Schools

Mollusc Characteristics
• Unsegmented soft body
– Visceral mass
• Molluscs have a Modified Foot
– Muscular foot and/or tentacles
• Have a mantle (fold in the body wall
that lines the shell)
• Most have shell (internal or external)
– Or remnants of a shell
• Pen in squid
Tentacles/
modified foot
head
Mantle
cavity
Mantle
foot
Shell
Classes of Molluscs
There are 8 classes of molluscs but this course will look at the 3 main classes
• Class Cephalopoda –
Octopus, squid
and nautilus
• Class Gastropoda –
slugs and snails
• Class Bivalvia – clams,
mussels, scallops
.
Class Gastropoda
• free-living; marine, terrestrial, fresh water
• noticeable head
• single shell, often spiral
• muscular foot is attached near the stomach area
Pallial Lung
• In the Pulmonata subclass, the species hallmark is a
functional lung, which the term, "pulmonate" refers to. The
mantle cavity walls have become heavily vascularized
and more or less form a lung sac ("pallial lung").
• By expansion and contraction of the mantle muscles, this
lung sac permits breathing air across a small opening to
the outside.
• Thus, oxygen and carbon dioxide gases can exchange
with the vascular system, and none of the pulmonate
snails have (or needs) the gill.
Class Cephalopoda
• Exclusively marine
• Shell- “pen”- internal
remnant of a shell
• Use fins and siphon to
move
• Modified foot= tentacles
• Fast swimming
predators
-use tentacles to catch
prey
• Have a special camera
like eye
Ex- Giant Squid
Squid External Anatomy
Fins
Mantle
Siphon
• Cephalopods are the only molluscs with a closed
circulatory system.
• They have three hearts total:
– two gill hearts (also known as branchial hearts) that move blood
through the capillaries of the gills.
– A single systemic heart then pumps the oxygenated blood
through the rest of the body.
• Like most molluscs, cephalopods use hemocyanin, a
copper-containing protein, rather than hemoglobin to
transport oxygen.
– As a result, their blood is colorless when deoxygenated and
turns blue when exposed to air.[13]
Squid Internal Anatomy
Class Bivalvia
• marine and freshwater
• gill used for gas exchange
• all are sessile, suspension feeders and
filter food from the water
• all have two part shells
(bivalves)
Other Bivalves
The bivalves are the second largest class of molluscs.
They differ from snails in having two shells, usually mirror
images of each other. Some like oysters and mussels live
attached to rocks and other hard surfaces while others, like
pipis, burrow in sand. Leptonoidean bivalves (in picture)
are a group which usually live commensally with other
animals. Most have a large foot and are active crawlers
(1mm).
•
Limatula strangei. Some bivalves, such as the
scallops are able to actively move when endangered
by vigorously flapping their shells and squirting out
jets of water. Limatula also moves very vigorously
when disturbed. The tentacles around the mantle
edge are sticky, very mobile and parts can break off
them when the animal is disturbed, leaving a
potential predator with a sticky writhing worm-like
object to deal with as the Limatula escapes
(25mm).