Biology/Marine Biology

Mr. Weinkle

Blue Crab Dissection Lab- 600 points


Purpose: To understand and describe the structure and biology of a crustacean. To compare the anatomy of the crustacean with other animals and our own.


External Inspection: All students should CAREFULLY draw and label the external anatomy of the crab. Take special note of ALL appendages including chelipeds, leg joints, pleopods, mouthparts, antennae and antennules, eyes and any other features. Note of the numbers of segments in each part. Use the dissecting scopes for closer looks. Measure the carapace and draw it carefully. Make drawings of the mouth parts. Compare the guide to the animal.

Internal dissection: Cut away the dorsal shell to reveal internal features. Use your scalpel to separate the membranes covering the organs from the carapace. STOP: Identify all visible organs before proceeding.†

DO NOT CRACK OR TEAR the exoskeleton. Write down what each is and what it does. Draw this view. Be sure to describe color and texture.

Locate and Identify:

1. Nervous system- brain and ganglia

2. Circulatory system- heart and blood vessels

3. Respiratory- Branchial chamber, gills and apertures (openings to the outside)

4. Digestive system- Mouth and mouth parts, gut system, intestine, anus

5. Muscular system- mouth parts, legs, muscles and joints.

Dissect the pincers (if present), make drawings and notes of the muscles. Dissect the ventral abdomen to reveal the muscles and other features. Describe your observations in drawings and notes. Be accurate and thorough. Do not take shortcuts. Think of the crab as a machine you are taking apart- donít break it.

On each step- THINK about what you are doing.

Results and Observations: All notes should be legible with corrected grammar and spelling. Include ALL observations regarding the animal. Label ALL drawings. Your notes should tell what YOU did and observed. Answer all questions. For full credit- improve your drawings and notes for the lab report submission. Do not copy the illustrations in the handout for your report. Illustrate what YOU see.

Conclusions: Do comment on the symmetry and structure of the animal and how it might relate to the habitat and behavior of the animal. DO comment on what the dissection teaches you about life and your body. If it teaches you nothing useful, explain why. Compare the crab to the earthworm. What evidence of segmentation do you see? How is the anatomy of the crab different than the earthworm, starfish, fish and clam?

Crab Anatomy- Glossary


Antenna- (pl. antennae) The long segmented appendages located behind the eyestalks. These allow the crab to interact with its environment by touch and chemoreception.

Antennule- (pl. antennules) Shorter segmented appendages located between and below the eyestalks, sensory organs; these also use chemoreception to "smell" and "taste".

Appendages- Ten legs (five pairs) including a claw-bearing pair with spines used for feeding and defense, followed by three pairs of sharply pointed walking legs, and a pair modified as flat swimming paddles at the rear, swimming legs.

Apron- Abdomen of a crab, which is folded under the body; male's is narrow and long. A mature female's is semicircular, like the dome of the capitol building.

Carapace- The shell covering the body. It provides protective covering. It is made of chitin and covers cephalothorax of the crab.

Cheliped- The first pair of legs, carries the large claw which is used for defense and obtaining food. Male's claws are blue tipped with red; female's are red.

Eyes- Visual organs mounted on the ends of eyestalks. The eyestalks contain cells that release hormones that inhibit molting and the development of gonads.

Lateral spines- Paired points on the widest outside edges of the carapace.

Mouth- Opening to the digestive system, located between the antennae. The mouth contains jaws that hold and push food into the esophagus.

Sponge- Egg masses. Numbers of eggs vary, some may contain as many as

8,000,000. They are attached to swimmerets.

Swimmerets- (pleopods) Paired abdominal appendages under the apron of the female crab on which the eggs are carried until they hatch.
Swimming Legs- The last paired abdominal appendages, flattened for swimming.

Walking legs- 3 pairs. Used for movement; crabs are capable of walking forward or diagonally, but usually they walk sideways.


Gills- Place of respiration and filtration, consisting of many plume-like filaments arranged around a central axis. There are eight gills on each side.

Heart- The pump of the circulatory system. It is broad in size and located in the lower center part of the body.

Hepatopancreas- Digestive gland. Large organ with several functions, including the secretion of digestive enzymes and absorption of digested food. It fills most of the area around the stomach, depending on its contents of food and water.

Intestine- Portion of the digestive system through which digested food passes.

Stomach- The organ of the digestive system that breaks down swallowed particles of food. It is lined with small hard plates and projections.

Testes- Part of the male reproductive system, located on top of the hepatopancreas on either side of the stomach.
Ovaries- Female reproductive organs that produce eggs and leading to the oviducts where eggs are released.

Cartilage- Encases muscles that aid in movement of the legs. The muscles are the edible portion of the crab.


These photos were taken in class of young blue crabs Callinectes sapidus, acquired from a local bait store Don's Bait and Tackle on US1 in Homestead, Florida.
The chelipeds (pincers) were removed by the crabber who caught these.

The first picture is a dorsal view:
crab dorsal view

The next is the face and mouth area:

crab face with mouth parts

this is the ventral view of a female with egg mass, note the oviducts:ventral view of female with egg mass

these next 5 pictures are internal views of the crab
The first the exposed internal view with membrane covering organs.
internal view with membrane

Note the digestive glands in the upper carapace.
internal view 2 with upper carapace removed and organs exposed

internal view of female with ovaries and adjacent organs exposed

The brain is located just below the antennules and connected to nerves running to the eyes,
antennae and ventral nerve via the circumesophageal ganglia.

brain and supraesophageal ganglion

Crab anatomy- dorsal external view

dorsal internal view

Ventral exterior view (male)