Name: _______________
Crayfish External Observation
Pre-lab:
1. Crayfish are in Domain ___________________.
2. Crayfish are in Kingdom ____________________.
3. Crayfish are in Phylum ____________________.
External Anatomy:
The Head:
 Place the crayfish in the tray so you can SEE the MOUTH
PARTS.
 Find the 1st, 2nd, & 3rd maxillipeds. The 3rd maxilliped is
the BIGGEST/TOPMOST, the 2nd is underneath, and the 1st is
under the 2nd. Maxillipeds are used to handle food.
 Find the mandible under the maxillipeds. The mandible
should be hard to move. The mandible is like the jaw in
humans.
Describe the difference between how a human jaw OPENS and
how a crayfish mandible OPENS.
 Find the 2 antennae and the smaller antennules that
branch from the base. These are sense organs. (touch,
taste, equilibrium)
Complete the chart
Part
Maxillipeds
Function
Mandible
Antennae
The
Body:
 Turn the crayfish over so you are looking at the back.
 Find the eyes at the end of 2 stalks called pedicles.
 The body of the crayfish is called the cephalothorax. The
cephalothorax is made up of the fused head and thorax.
The cephalothorax is covered by a thick armor called a
carapace. The pointy part of the carapace is called the
rostrum.
 The abdomen of the crayfish is segmented and flexible.
BEND the abdomen CAREFULLY BACK and FORTH and see
how each segment moves.
Count the number of segments on the abdomen. (HINTBending it will show you WHERE the segments are separated.)
HOW MANY segments are on your crayfish? __________
IS this the same as the other crayfish in the class? _________
The Appendages:
 Find the claws – chelipeds. GENTLEY move the chelipeds
to see in what direction they move.
HOW MANY joints are on a SINGLE cheliped? __________
 Find the 4 pairs of walking legs. They are behind the
chelipeds.
HOW MANY joints are on a SINGLE walking leg? __________
 TURN YOUR CRAYFISH OVER – Find the swimmerets
(appendages attached to each segment of the abdomen).
ARE the swimmerets jointed? __________
HOW MANY PAIRS of swimmerets are there? __________
 The LAST segment of the abdomen (7th) is the telson. It is
specialized for swimming. Find the 2 uropods that extend
off both sides of the telson.
 Make a DORSAL scientific drawing and label the following:
eye, telson, uropod, cephalothorax, carapace, rostrom,
chelipeds, walking legs, antennae, and antennulues.
 Make a VENTRAL scientific drawing and label the following:
swimmerets, mandible, 1st maxillipeds, 2nd maxillipeds, and
3rd maxillipeds.