This document contains diagrams and descriptions of the external and internal anatomy of a crayfish. It identifies and describes key external structures like the cephalothorax, abdomen, appendages, eyes and sensory organs. Internally, it outlines the location of organs like the heart, hepatopancreas gland, stomach and nerve cord. Descriptions are provided of both male and female reproductive structures and swimming appendages.

3. Dorsal View
1. These are the crayfish's uropods. It has two pairs of these appendages.
2. This is the crayfish's telson. It is used in combination with the uropods for
backwards escape swimming.
3. This is the crayfish's abdomen. Its paired appendages are the swimmerets and uropods.
4. This is the crayfish's cephalothorax. It is covered with a carapace that offers some
protection from predators.
5. This is the cephalic groove, a lateral seam in the carapace between the head and thorax
regions.
6. These are two of 8 (4 pairs) of walking legs. Each walking leg has an attached gill that
is found just beneath the exoskeleton.
7.. This is the crayfish's left cheliped. These appendages are used for defense and food
handling.
8. This is the crayfish's left eye.
9. This region of the carapace is called the rostrum.
a This is the crayfish's left long antenna, a sensory organ.

5. Mouth Area
1. The crayfish has four pairs of walking legs.
2. The arrows point to appendages off of several of the
crayfish's 3 pairs of maxillipeds.
3. The arrow points to the crayfish's right mandible. The
mouth is in this area.
4. The arrow points to a renal pore, an opening of the
crayfish's excretory organ, the green gland.
5. The arrow points to one of the long antennae.
6. The arrow points to one of the short antennae (or
antennules).
7. This is the crayfish's right cheliped.

7. Ventral View
1. These are the crayfish's uropods. It has two pairs of these
appendages.
2. These are the crayfish's swimmerets. There are five pairs of
these appendages.
3. These are the crayfish's walking legs. There are four pairs of
these appendages.
4. This is the crayfish's right cheliped. These appendages are used
for defense and food handling.
5. This specimen is a male. It's first two pair of swimmerets are
elongate and form a sperm transfer organ. In females, the
first two pairs of swimmerets are unmodified.
6. This is the crayfish's right long antenna, a sensory organ.

9. Male
1. This is a swimmeret, a short, filamentous appendage.
2. The pin points to the male genetal opening. Sperm are released here and
delivered by the male's modified swimmerets to the female's seminal
receptacle.
3. In the male, the first two pairs of swimmerets are longer, and prong-shaped.
They serve as a sperm transfer organ during mating. In this photo, the
right modified swimmeret has been pushed aside, while the left one is in place.
4. This is the base of the fifth pair of walking legs.
5. This is the base of the fourth pair of walking legs.
6. This is the base of the third pair of walking legs.
7. This is the base of the second pair of walking legs.
8. This is the base of the first pair of walking legs, called the chelipeds.

11. Female
1. The arrows point to several swimmerets, short, filamentous
appendages that are unmodified in the female.
2. The arrow points to the seminal receptacle. Sperm received
from the male are stored here until the female releases eggs.
3. This is the base of the fifth pair of walking legs.
4. This is the base of the fourth pair of walking legs.
5. The female genital openings are located on the bases of the third
pair of walking legs. The arrow points to an opening.
6. This is the base of the second pair of walking legs.

14. Cephalothorax (dorsal)
1. The arrow points to a gill within the exposed branchial cavity. They are
attached directly to the walking legs. This forces water over them when
the crayfish moves.
2. The arrow points to the crayfish's heart.
3. The arrow points to a portion of the crayfish's hepatopancreas gland.
4. The arrow points to the mandibular adductor muscle. It was attached to the
inner surface of the carapace. It's contraction causes the mandibles to
come together.
5. The arrow points to the gastric stomach, the portion of the digestive system
containing the gastric mill, a chitinous arrangement of teeth, files, and
sieves used to grind up the food.
6. The arrow points to the crayfish's right eye.

16. Branchial Chamber
1. The arrows show where the gills are attached to each of the five pairs of walking
legs.
2. The carapace covering the right branchial chamber has been removed showing
the gills. Water is drawn into the posterior end of this chamber, flows across
the gills, and leaves via the anterior end.
3. This is the cephalic groove, a lateral seam in the carapace between the head and
thorax regions.
4. The arrow points to the right third maxillilped.
5. This is the crayfish's right cheliped. These appendages are used for defense and
food handling.
6. This is the crayfish's right eye.
7. This region of the carapace is called the rostrum.
8. This is the crayfish's right long antenna, a sensory organ.

18. •Cephalothorax (lateral)
1. The arrows point to the cut bases of walking legs 3, 4, and 5.
2. This is the right branchial chamber. The gill filaments have been
trimmed to reveal deeper structures.
3. The arrow points to the heart. Click within the yellow rectangle to
see an isolated crayfish heart.
4. The arrow points to a portion of the crayfish's hepatopancreas gland.
5. The arrow points to the stomach. Click within the yellow rectangle to
see a dissection of the gastric mill within the cardiac portion of the
stomach.
6. The arrow points to a green gland. These organs help the crayfish get
rid of excess water and ammonia.

20. Cephalothorax, deeper (dorsal)
1. The arrow points to a portion of the crayfish's hepatopancreas gland.
2. The arrow points to a green gland. These organs help the crayfish get rid of excess
water and ammonia.
3. The arrow points to the cut gut tube at the level of the esophagus. The stomach
has been removed.
4. The arrows point to the ventral nerve cord. The brain is anterior and not visible.
The nerve cords leave the brain, go around the the esophagus, and become the
ventral nerve cord, characteristic of the arthropods.

22. Abdomen (dorsal)
1. These are the crayfish's uropods. It has two pairs of these appendages.
2. This is the crayfish's telson. It, in combination with the uropods, is used in
rapid, backwards escape swimming.
3. These are the crayfish's abdominal flexor muscles. They provide the major
force for rapid backwards swimming by flexing the tail.
4. These are the crayfish's intestine.
5. The arrow points to the porterior portion of the crayfish's right branchial
chamber.