A quick guide to crayfish anatomy

In using keys to identify crayfish (or in describing the differences between male and female crayfish), it can quickly become a confusing word soup of technical terms. This section will help you wade through the jargon-y maze of words used to describe the anatomy of crayfish.

What features to look for on a crayfish: A: coloration, B: Areola width, C: Rostrum shape, D: Claw length, E: Carapace length, F: Thumb shape
  • (A) coloration
  • (B) areola width
  • (C) rostrum shape
  • (D) chelae (claw) length
  • (E) carapace length
  • (F) dactyl (thumb) shape.

Glossary of Anatomical Features on Crayfish

ABDOMEN the tail of a crayfish, posterior to the cephalothorax
ACUMEN the apical projection on the rostrum; sometimes with marginal spines
ANNULUS VENTRALIS (gonopore) the circular seminal receptacle on females, found between the abdomen and cephalothorax (between 4th and 5th pereiopods).
AREOLA the space between the 2 carapace plates
BROOD the offspring produced at a single hatching, carried in the first 2-3 molts as on the female’s abdomen
CARAPACE the part of a crayfish’s exoskeleton that covers the cephalothorax
CEPHALOTHORAX the fused portion of a crayfish’s body that contains the head and the thorax
CERVICAL GROOVE transverse line that separates the head (cardiac) and thorax (gastric) regions
CHELAE the claw of a crayfish, made up of the two fingers (dactyl and propodus) and the palm
DACTYL the movable finger on a chela
EXOSKELETON The hard chitinous outer covering (skeleton) of arthropods; this covering is shed during molting.
EXUVIUM the exoskeleton shed during a molt
FINGER the 2 long digits (dactyl and propodus) at the end of a chela
F1 (FIRST-FORM MALE) at maturity, the form of a reproductively active male; the exoskeleton has hooks and stiffened gonopods
F2 (SECOND-FORM MALE) the form of a male that is not reproductively active; lacks hooks and stiffened gonopods
GILLS feathery structures on the ventral surface of the carapace used for respiration
GONOPODS on males, the first pair of pleopods, or swimmerets used in reproduction to transfer sperm
HOOKS projections on the ischia of a pair of walking legs on males, used to grasp onto females during mating
INSTAR the phase between molts
“IN BERRY” describes a female who is carrying eggs or young on her abdomen
PALM the wide base of a chela to which the fingers are attached
PEREIOPODS the 5 pairs of walking legs attached to the cephalothorax
PLEOPODS the 5 pairs of swimmerets attached to the abdomen
PROPODUS the immovable finger that extends up from the palm of a chela.
ROSTRUM the nose of a crayfish
SETAE hairlike projections on the surface of the exoskeleton, often between the fingers of chelae
SPINE the sharpened bumps or projections on the carapace
TERMINAL ELEMENTS the projections at the tips of the male reproductive structures (gonopods)
TUBERCLE the raised blunt bumps or projections on the exoskeleton, typically contrasting color to carapace