The Crayfish of Nebraska

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Page 18 of 148

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

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