Clam Dissection
Introduction - Background
The phylum _MOLLUSCA_includes snails, clams, chitons,
slugs, limpets, octopi, and squid. As mollusks develop
from a fertilized egg to an adult, most pass through a
larval stage called the __TROCHOPHORE___, which is a
ciliated, free-swimming stage. Mollusks also have a
_RADULA__or file-like organ for feeding, a
_MANTLE__that may secrete a shell, and a muscular foot
for locomotion. Clams are marine mollusks with two
__VALVES___or shells. Like all mollusks, a clam has a
mantle which surrounds its soft body. It also has a
muscular foot, which enables the clam to burrow itself in
mud or sand. The soft tissue above the foot is called the
__VISCERAL MASS___and contains the clam's body
organs.
Taxonomy of the Clam
Kingdom - __ANIMALIA__
Phylum - __MOLLUSCA____
Class - __BIVALVA__ or Pelecypoda
Lab Questions:
1.a) Give the kingdom, phylum and class for the clam.
KINGDOM = ANIMALIA
PHYLUM = MOLLUSCA
CLASS = BIVALVA / Pelecypoda
b)What is the oldest part of a clam's shell called and how can it
be located?
It is the Umbo, and it is the coiled up hump like structure
with the tight rings.
c). Why are clams called bivalves?
BI = Two
VALVE = Shell
2. What do the rings on the clam's shell indicate?
They indicate how old the clam is; the more rings the older
the clam.
3. What is the function of the tooth-like projections at the dorsal
edge of the clam's valves?
These microscopic teeth help make sure that the valves align
properly while closing. To make sure that the shells form a
tight seal of protection.
4. What is the mantle cavity?
The large space found between the two lobes of mantle.
Water flows through this space and the food and visceral
mass are located in this cavity.
5. Where are the incurrent and excurrent siphons located and
what is their function.
Excurrent siphon is a hole between the two lobes meet at the
posterior end of the clam. It is found more dorsal than the
incurrent siphon. The excurrent gets rid of waste water and
wastes, while the incurrent brings in fresh water, food and
gases.
6. How do clams breathe?
Clams use two pairs of feathery gills for respiration (gas
exchange), as oxygen diffuses into the gills.
7. Describe the shape of the clam's foot.
It is wedge/axe shaped to help it dig.
8. Where are the palps found and what is their function?
A pair of labial palps are located at the anterior end of each
set of gills. They direct the trapped food toward the mouth.
9. Describe the movement of food from the incurrent siphon
through the digestive system of the clam.
Plankton  Incurrent siphon  Mucous on gills  cilia
toward labial palps  Labial palps  Mouth  Stomach 
Intestine  Anus  Excurrent Siphon.
10. Why are clams referred to as "filter feeders"?
They filter plankton out of the water and trap it and direct it
to their digestive tracts.
11. Label the internal structures of the clam (use your diagrams
from Unit 6 Notes #1)
HEART
UMBO
Intestine
STOMACH
Posterior Adductor Muscle
MOUTH
ANUS
Anterior Adductor Muscle
Excurrent Siphon
Labial Palp
Incurrent Siphon
Intestine
GILLS
FOOT
MANTLE
GONAD
SHELL / Valve