Download Carefully remove all jointed appendage of the crayfish.

Crayfish Anatomy
Introduction
Crayfish are in the phylum Arthropoda, which includes other animals such as spiders and insects. Arthropods are characterized
by having jointed appendages, segmented bodies and an exoskeleton. Crayfish belong to the subphylum Crustacea, which
includes: shrimp, crab, barnacles, isopods and water fleas.
A.
External Anatomy
Place the crayfish in the pan with its dorsal side up. Feel the hard exoskeleton, which is made up of a hardened protein
called chitin.
Bogy Regions – The crayfish’s body is divided into two major regions: the cephalothorax and the abdomen. The
cephalothorax consists of the cephalic (or head) and thorax and is covered by a piece of exoskeleton called the carapace.
Note the curved cervical groove marking the division between the head and thorax (at some point in this animal’s
evolutionary history, it may have had a separate head and thorax.) The pointed, beaklike structure at the anterior end of the
carapace is the rostrum. The stalked, compound eyes are located on each side of the rostrum. The last segment of the
abdomen is called the telson. The two pair of appendages on each side of the telson are called uropods. Together they
are called the tail fan.
Appendages – Turn the crayfish over to expose its ventral side. Note the many paired appendages. Crayfish have the
ability to regenerate lost body parts, so you may find an appendage that has only partially regrown. Protruding from the
head are two long antennae, organs of touch, taste and smell. Two shorter branched antennules are located between the
antennae and are used for balance, touch and taste. Locate the mouth opening. Surrounding the mouth are jagged jaws
called mandibles, used for crushing food. Posterior to the mandibles are three of pairs of maxillae. These are used to hold
solid food, tear food and to help move water over the gills. The three pairs of leg like maxillipeds help hold foot while eating.
The four pairs of appendages on the cephalothorax are the walking legs. The large, pincer like appendages are the
chelipeds (“pinching legs”), which the crayfish use for defense and grasping food.
On the abdomen, note the small appendages called swimmerets. These are used in swimming and reproduction. The first
pair of swimmerets are small on a female crayfish and can be used to hold eggs or newborns. Females will also have a
small crescent-shaped slit at the base of the third pair of walking legs. This is the genital pore and it is where sperm will
enter the female. On a male crayfish, the first two pairs of swimmerets are large, stiff and are folded forward to transfer
sperm to females. Males also have sperm duct openings on the base segment of the fourth pair of walking legs. Compare
the crayfish of others to help see the difference in swimmerets. The anus is located in the center of the telson.
Carefully remove all jointed appendage of the crayfish.
B.
Internal Anatomy
Using one hand to hold the crayfish dorsal side up, use scissors to carefully cut through the back of the carapace along the
cut line 1, as shown below. Cut along the indentations that separate the thoracic portion of the carapace into three regions.
Start the cut at the posterior edges of the carapace and extend it along both sides in the cephalic region. Make shallow
cuts and use forceps to carefully lift away the carapace.
Place the specimen on its side, with the head facing left. Using scissors, start cutting at the base of cutline 1 and cut along
the side of the crayfish, as illustrated by cutline 2. Extend the cut line forward toward the rostrum. Use forceps to carefully
lift away the remaining parts of the carapace, exposing the underlying gills and other organs.
Respiratory system – The exposed feathery gills are found underneath the carapace and are attached to the chelipeds
and walking legs. A constant flow of blood the gills releases carbon dioxide and picks up oxygen.
Circulatory system – Separate the dorsal muscle layer in the thorax to expose the dorsal, tubular heart. It is vase shaped,
light in color and is used to pump blood to the animal. Blood is moved to the anterior and posterior of the animal with a
dorsal artery. The depressions on the heart are small openings called ostia. These openings allow to blood to enter back
into the heart.
Remove the heart and the muscles at the sides of the thorax to reveal the organs underneath.
Reproductive system – If the crayfish is male, you will see a small pair of white Y-shaped testes (sperm producers) below
and a little in front of the heart. Sperm ducts extend from the Y to the base of the fifth pair of walking legs. If your specimen
is a female, locate the bi-lobed ovary (egg producers). It is in the same relative position as the testis, but they appear as a
large, reddish mass under the heart. Short oviducts, which are the passageway for eggs, extend from near the center of
each side of the ovary and open at the third walking leg.
Mating takes place in the fall. Sperm pass from a male’s testes through the ducts to the outside. Using the modified
swimmerets, the male transfers his sperm to the female’s seminal receptacle, through her genital pore, where the sperm
are stored over the winter. The eggs are not fertilized until the female lays them in April.
Insert the point of the scissors under the dorsal side of the abdominal shell and cut back to the telson. Spread the shell to
expose the organs underneath.
Digestive System – Food enters the digestive tract through the mouth and travels through the short esophagus to the
stomach. The large, thin-walled, lobed stomach is located in the middle of the cephalothorax. The stomach contains rows
of chitinous teeth.
On each side of the stomach are yellowish digestive glands. They secrete digestive enzymes into the stomach.
Undigested material passes from the stomach into the intestine. This tube lies on top of the abdominal muscles and runs to
the ventral surface of the telson. Waste passes out of the body through the anus. If you are eating fresh crayfish, you must
first remove the intestine as to not spoil the meat. You grab and twist the telson, which removes the anus and intestine.
Remove the digestive organs as follows. Cut through the esophagus and the bands of muscles behind the eyes that hold
the stomach. Lift out the stomach and any structures that are connected to it.
Nervous System – Carefully cut away the rostrum and any remaining carapace. Between the eyestalks is the brain, a
small white mass. There are many nerves traveling from the brain to the eyes and antennae.
The brain, which is located behind the compound eyes and anterior the mouth, has two large nerves which surround the
esophagus and connects to the ventral nerve cord. The nerve cord runs the length of the body and contains many
specialized clumps of nerves called ganglia.
Each of the crayfish’s compound eyes is made up of long visual rods. The outer surface of each rod is called a facet. Light
is focused through each facet onto the retinas, producing a fuzzy but wide-ranging image. Examine an eye with a
dissecting microscope. Note the numerous facets in each eye. Because the eyes are on movable stalks, the crayfish has a
very wide field of view. The sense of touch is probably more important in the crayfish than vision. Touch receptors are
located in specialized hairs on the body as well as on some appendages.
Excretory System – Carefully remove any remaining tissue in the head to expose the large pair of green glands, which are
just behind the antennules. The green glands empty liquid wastes into the surrounding transparent bladder. A duct from
the bladder opens to the exterior.
Nervous System – Carefully cut away the rostrum and any remaining carapace. Between the eyestalks is the brain, a
small white mass. There are many nerves traveling from the brain to the eyes and antennae.
The brain, which is located behind the compound eyes and anterior the mouth, has two large nerves which surround the
esophagus and connects to the ventral nerve cord. The nerve cord runs and length of the body and contains many
specialized clumps of nerves called ganglia.
Each of the crayfish’s compound eyes is made up of long visual rods. The outer surface of each rod is called a facet. Light
is focused through each facet onto the retinas, producing a fuzzy but wide-ranging image. Examine an eye with a
dissecting microscope. Note the numerous facets in each eye. Because the eyes are on movable stalks, the crayfish has a
very wide field of view.
Crayfish Dissection labeling and questions
On the diagram of the dorsal surface below, label the cephalothorax, abdomen, cervical groove, rostrum,
compound eye, telson and uropod.
On the diagram of the ventral surface below, label the following: mouth, mandible, antennae, antennule, cheliped,
walking leg, swimmeret and anus.
On the diagram of the internal anatomy, label the heart, ostia, dorsal artery, ovary, genital pore, esophagus,
stomach, digestive gland, intestine, anus, green gland, brain, nerve cord, and ganglia.
1.
Write down the function of each appendage:
a. Antennules
b.
Antenna
c.
Mandible
d.
Maxilla
e.
Maxillipeds
f.
Chelipeds
g.
Swimmerets
h.
Uropod
i.
Telson
2.
What protein makes up the structure of the exoskeleton?
3.
What is the rostrum?
4.
How is the tail fan and the flexing of the abdomen an adaptation for the crayfish?
5.
What sex is your crayfish?
a.
What external structures can be used to determine crayfish gender?
6.
Why is the large surface area of the gills beneficial for the crayfish?
7.
What is the purpose of a seminal receptacle?
8.
What are the chitinous teeth in stomach used for?
9.
Beside each structure listed below, write the system to which it belongs.
anus-
ostia-
bladder-
green glands-
antenna-
mandible-
esophagus-
facet-
ganglia-
10. In the crayfish, blood is pumped into spaces called sinuses around the organs. After delivering oxygen and picking up
wastes, the blood drains back into the heart through the ostia. What type of circulatory system is this?
11. What is the function of the oviduct?
12. What is the function of the genital pore?
13. To what structure in humans is the green gland comparable?
14. What is the advantage of having eyes on stalks?
15. Name the three characteristics exhibited in crayfish that are found in all arthropods.