Glossary of Crustacean Terms


Term Definition

The body segments posterior to the carapace. Made of 6 segments, including the telson. In crabs, the abdomen is the flap that is flexed underneath the body.

antenna (pl. antennae)

The long segmented appendages originating from behind the eyestalks.


The short segmented appendages located between and below the eyestalks

antennule peduncle

The basal portion of the antennule.


To the front.


The opening into the body chamber between the scuta of a barnacle.


The upper angle of the opercular plates in barnacles.


The abdomen which forms a flap that is flexed underneath the body of the crab.

basal margin

The lower margin of a plate in barnacles.

basal plate

The bottom plate and place of attachment for barnacles. May be calcareous or membranous.


The lower curved angle of the scutum in goose barnacles or the apex of the tergum with a curved beak-like point in other barnacles.


Having two points.


The portion of the barnacle above the peduncle (shelled part) of a goose barnacle.


The hard dorsal covering of the head and thorax of the body. Does not cover the abdomen.

carapace length

The distance from the anterior most part of the head (usually the rostrum) to the posterior most part of the carapace (dose not include the abdomen).

carapace width

In crabs, the distance between the lateral spines (the posterior most spines) of the carapace. This measurement is usually used to describe crab size.


A raised ridge. In goose barnacles, an unpaired narrow plate adjacent to the paired scutum and tergum plates. One of the parietes in other barnacles.


The 3rd segment from the distal end of a crab leg. In a clawed leg, it is the segment where the appendage flexes (i.e. the elbow).


The fused head and thorax of many crustaceans.

chela (pl. chelae)

The last two segments of a leg that forms a pincer or claw. It includes the movable and immovable fingers and the palm, except in mantis shrimps (no movable finger).


Possesses a chela (claw).


The 1st pair of legs (anterior most) when they have claws.

cirrus (pl. cirri)

Biramous appendages in barnacles used to filter the water for food.

claw appendage

The entire appendage that possesses a claw, from the fingers to the point of attachment to the body.


Curving inward.


Curving outward.

crest of claws

An elevated, irregularly toothed ridge


An invertebrate with a segmented body, a hard external shell (exoskeleton), paired and segmented appendages and have 2 pairs of antennae. Includes shrimp, crabs, lobsters, barnacles and mantis shrimps.

dactylus (dactyl)

The segment of a crab leg that is most distal (farthest) from the body. In a clawed leg, it is the movable finger segment.


Farthest from the center of the body.


Pertaining to the top (back).


Upper part of sides.


The inner pair of flattened appendages of the tail fan or at the end of a biramous segment.


The outer pair of flattened appendages of the tail fan or at the end of a biramous segment.


Scale-like structure at the base of the eye stalk.


The parts of the claw that opposes each other, one being movable, the other stationary.

hepatic spine

Spine on the anterior lateral side of the carapace, behind and slightly below the eye orbit.

immovable finger

The finger of the claw that does not move.


The edge of the carapace between the orbits (eye sockets)


A ridge.


The sides of a body.

lateral spine

The spines on the outside edges of the carapace at its widest point (usually the posterior most spines on the sides).

length of crab

Usually refers to the carapace width. If a strong rostrum is present, length is sometimes reported as the carapace length.

length of shrimp

The distance from the tip of the rostrum to the tip of the telson.

major cheliped

The largest clawed appendage when the claws are unequal in size.


In a clawed leg, the manus makes up the immovable finger and palm. The propodus.


The three outer pairs of mouth appendages.


The 4th segment from the end of a leg appendage.


Areas of color with no particular shape or pattern.

movable finger

The finger of the claw that is movable.


A small lump or knot.


Angled, either upward or downward, usually refers to mouths, stripes or lines.

opercular plates

The movable plates in the orifice of the shell in barnacles. Consists of the paired scuta and paired terga.


The eye socket.

orbital teeth

Projections or spines flanking each side of the eye socket.


The dorsal opening of the shell in barnacles.


The part of the claw behind the movable and immovable fingers.

paries (pl. parietes)

A triangular plate on a barnacle.


A fleshy stalk between the shell and substrate, in goose barnacles.


In shrimp, the 1st 5 pair of long walking legs, attached to the cephalothorax, the 1st few of which may or may not be chelate.


Genital structures attached to the 1st pair of swimming legs in male penaeid shrimp. Looks like a pair of extensions, one from each leg with ends united together in larger shrimp.


In shrimp, the paired swimming legs that are attached to the abdomen, usually biramous.


To the rear.


The second segment from the distal end of a leg. In a clawed leg, the propodus is the segment with the immovable finger and palm.


Nearest the center of the body or point of attachment to body.

radius (pl. radii)

The walls in between the triangular plates in barnacles.


An extension of the carapace between the eyes projecting anteriorly.

scutum (pl. scuta)

One of a pair of internal opercular plates in barnacles (in goose barnacles, the lower external triangular plate).



setae (plural of seta)

Small hairs


A sharp pointed projection.


A marine crustacean with strongly toothed, scissor-like claws and have gills on their abdomen. Also called mantis shrimps.


The abdomen, in shrimp.

tail fan

Two pairs of flattened appendages that attach to the last segment of the abdomen. The uropods.


Projections or spines.


The most terminal segment of the abdomen. Forms the center part of the tail fan.

tergum (pl. terga)

One of a pair of internal opercular plates in barnacles (in goose barnacles, the upper external plate).

tergum spur

A projection on the basal margin of the tergum in barnacles.


External pocket on the underside of the thorax of female penaeid shrimp, used for receiving the male sperm sac. Usually covered by 2 lateral plates (absent in white shrimp).

third maxillipeds

The outermost part of the mouth appendages.

thoracic segment

A segment between the carapace and the abdomen in mantis shrimp. The last pairs of walking legs are attached underneath.


The part of the body between the head and abdomen.


A calcified and hard protuberance.


Two pairs of flattened appendages that attach to the last segment of the abdomen. The tail fan.


Pertaining to the underside or bottom.

walking legs

Legs that are used for walking that do not possess a claw (except in shrimp, may be chelate.)