Mollusc Characteristics

1

2
Mollusc Characteristics
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

3


Tentacles/ modified foot
Shell
foot
Mantle
head
Mantle cavity
4
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

5
(No Transcript)
6
Class Gastropoda

• free-living marine, terrestrial, fresh water
• noticeable head
• single shell, often spiral
• muscular foot is attached near the stomach area

7
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.

8
(No Transcript)
9
(No Transcript)
10
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
11
Squid External Anatomy
Fins
Mantle
Siphon
12
Closed Circulatory System!!!

• 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

13
(No Transcript)
14
Squid Internal Anatomy
15
(No Transcript)
16
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)

17
(No Transcript)
18
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).