10
ANATOMY
EXTERNAL ANATOMY
The photo above illustrates the major
external anatomical features of the crayfish.
[Various measurements and ratios of
crayfish body parts are contained in Section
VI.] The thorax and head are divided by a
cervical groove and together are called the
carapace or cephalothorax. In the center
of the thorax are two curved edges marking
the aureola. Protected and hidden by the
thorax on the sides are the gills. The
rostrum is the forward extension of the
head over the eyes. The eye is a compound
eye on a movable stalk. There are two long
antennae and between these are four short
antennules. Crayfish are members of the
decapoda which means "ten footed". There
are five pair of walking legs or periopods
which are numbered from 1 to 5. Number
1 is the large cheliped which is used to
gather food, for defense and for mating
Legs 2 and 3 have a tiny claw that can be
used both for
walking and
for picking up
items of food.
Legs 4 and 5
are true
walking legs
which have a
single point.
Each of the
segments of
the abdomen
has a pair of
pleopods.
The first
pleopod is
used by the male to transfer sperm to the
female's seminal receptacle. In the female,
the pleopods are where the eggs attach and
hatch. The tail consists of a central telson
which is flanked on either side by a pair of
