Glossary of Crustacean Terms

Check the crustacean glossary for definitions of terms used in our articles and elsewhere.

Abdomen
Muscular, segmented body part, posterior to the thorax; the edible "tail" portion of a lobster or shrimp
Abundance
Number of individuals in a particular area
Annelid
Segmented worm in Phylum Annelida; includes earthworms, marine worms, and leeches
Anterior
Toward the head end; opposite of posterior
Antenna
Elongated, movable sensory structure found on the head
Antennule
Sensory structure, smaller than the antennae and located more toward the midline of the body than the antennae
Anus
Posterior opening of the digestive tract
Appendage
Limb; leg, for example
Apron
Folded-under abdomen of a crab
Arthropod
Member of Phylum Arthropoda having a hard exoskeleton and jointed legs; includes insects, crustaceans, and arachnids

Backfin
Paddle-shaped posterior leg on a swimming crab
Benthic
On or associated with the bottom of a body of water
Berry crab
Female crab carrying eggs
Book gills
Gills composed of thin plates, constructed like the pages of a book
BRD
Bycatch Reduction Device; a device installed in a net to allow the escape of non-targeted species
Buster
Blue crab that has split at the back of the carapace in preparation for molting
Bycatch
Non-targeted species that are caught with the targeted species

Carapace
Dorsal covering of the body in many arthropods
Carnivore
Animal that eats only animals
Carpus
"Forearm" portion of a crab claw
Cephalothorax
Body segment consisting of the head and thorax fused together
Chelicera
Small feeding appendage found in Chelicerates
Chelicerate
Arthropod of Subphylum Chelicerata; includes horseshoe crabs, spiders, and scorpions
Cheliped
Claw of a crustacean; it is actually a modified walking leg
Chitin
Polysaccharide that makes up the exoskeleton
of an arthropod Class
Level of scientific classification; below Phylum and above Order
Climate
Average weather of an area, usually averaged over at least 10 years
Clutch
Batch of eggs extruded during a single spawning
Coagulate
To clot
Cohort
All individuals of a species hatched or born during a certain time period
Community
All the species within a particular area
Compound eye
Eye formed of multiple lens components
Crusher
Large, heavy claw used for crushing hard-shelled prey
Crustacean
Primarily aquatic arthropod of Subphylum Crustacea; includes crabs, isopods, krill, and barnacles

Decapod
Crustacean of Order Decapoda having ten legs; includes crabs, lobsters, and shrimp
Dispersal
Movement of individuals away from the place of birth
Diversity
A measure of the number of different things; e.g., species diversity is the number of different species in an area
DNA
Deoxyribonucleic Acid; the molecule that carries the genetic code
Domain
Broadest level of scientific classification; above Kingdom
Dorsal
Toward the back of the body; opposite of ventral
Doubler
Mating pair of crabs

Entrain
To capture and pull along
Escape ring
Open area in the wire of a crab trap that allows escape of crabs smaller than the legal size
Estuary
Semi-enclosed body of water where freshwater and saltwater meet
Evolution
Change over time
Exoskeleton
External skeleton; the shell of a crustacean
Exotic species
Species not native to an area
Exploit
To use or take advantage of

Family
Level of scientific classification; below Order and above Genus
Filter feeder
Organism that strains water to capture small food particles
Fishery
Population of aquatic organisms that supports a commercial or recreational industry
Fishing effort
Amount of time and equipment devoted to catching a target species
Fishing season
Time of the year when a species can legally be caught
Floater
Stone crab that has recently molted; if the claws are put in a pot of water they will float
Fouling community
Accumulation of organisms attached to an underwater object; e.g., barnacles and algae

Genetic distance
Measure of the proportion of genetic differences between individuals, populations, or other taxonomic classes
Genetics
Science dealing with heredity and variation of traits
Genus
Level of scientific classification; below Family and above Species
Gizzard
Organ for grinding food; usually found in animals lacking teeth or mandibles

Habitat
Specific environment in which an organism lives; will include the physical space and environmental conditions
Harvest
Total quantity (usually number or pounds) of an organism removed from an area over a specific amount of time
Hemocyanin
Molecule in blood that is based on copper, giving it a bluish color; found in most crustaceans, horseshoe crabs, and mollusks
Herbivore
Animal that eats only plants
Hybrid
Offspring resulting from the mating of two different species
Hypothesis
Idea or working explanation that can be tested

Interbreed
When members of two populations mate and produce offspring; interbreeding of two different species will produce hybrid offspring
Intertidal
Associated with the area of the shore between low and high tide lines
Invertebrate
Any animal that is not a member of Subphylum Vertebrata; an animal without a backbone

Jimmy
Male blue crab
Juvenile
Young, immature life stage

Kingdom
Level of scientific classification; below Domain and above Phylum

LAL
Limulus Amoebocyte Lysate; found in horseshoe crab blood, this substance clots in the presence of bacterial toxins; it is used to test for contamination
Landings
Quantity (usually pounds or numbers) of individuals brought to shore
Larva
Early life stage of some animals; this stage often looks very different than the adult
Lateral
Toward the sides; opposite of medial
Limited entry
Only a certain number of licenses are awarded for a particular fishery

Management plan
Government plan developed to ensure the sustainable harvest of a species
Mandible
Mouthpart used for crushing hard prey
Manus
"Hand" portion of a crab claw
Maturity
When an organism is capable of reproduction
Medial
Toward the center; opposite of lateral
Megalopa
Transitional stage between a crab larva and a juvenile
Merus
" Upper arm" portion of a crab claw
Migration
Movement from one area to another
Mollusk
Member of Phylum Mollusca having a soft body and usually a shell; includes clams, snails, and octopuses
Molt
To shed an exoskeleton; this process is necessary to allow for growth
Mortality
Rate at which organisms are removed from the population; death rate
Mutation
Sudden change in the genetic material that can be inherited by offspring

Nocturnal
Active at night

Offspring
Individuals produced from a mating
Ommatidia
Single lens component of a compound eye
Omnivore
Animal that eats both plants and animals
Operculum
Hard cover protecting gills
Order
Level of scientific classification; below Class and above Family
Overfishing
When harvesting of a population exceeds the population's ability to replenish itself
Ovigerous
Bearing eggs; i.e., a crab carrying eggs is considered ovigerous

Parasite
Organism that lives on and harms another organism
Peeler
Blue crab in the process of molting
Penaeid
Shrimp of Family Penaeidae; includes pink, brown, and white shrimp
Photoreceptor
Sensory structure that detects changes in light levels
pH
A measure of the level of acidity of a solution
Phylum
Level of scientific classification; below Kingdom and above Class
Pincher
Thin, tapered claw used for tearing
Pink sign
Blue crab that is 3-6 days from molting
Plankton
Organisms that cannot swim or are very weak swimmers and are at the mercy of the currents
Population
All individuals of a species found in a specific area
Portunid
Crab of Family Portunidae; includes blue crabs and pass crabs
Posterior
Toward the tail end; opposite of anterior
Predator
Animal that captures its prey live
Propodus
Immovable component of the pinching part of a claw
Pusher leg
Posterior leg in horseshoe crabs; it is fringed and used for crawling on land

Red sign
Blue crab that is 1-3 days from molting
Recruitment
Entry of individuals into a particular population, life stage, age, or size category; e.g., recruitment into the stone crab fishery occurs when crabs reach legal size
Regeneration
To regrow a body part that has been lost; crabs can regenerate lost claws
Reproductive isolation
When two populations are incapable of interbreeding due to physical, temporal, or biological barriers

Salinity
Saltiness of the water; usually measured in parts per thousand (o/oo)
Sally
Immature female blue crab
Scavenger
Animal that feeds on dead organisms or organic matter
Sex ratio
Number of males versus females in a population
Soft-shell
Crab that has recently molted and has not yet hardened its new exoskeleton
Sook
Mature female blue crab
Spawn
To release sperm and eggs
Species
Most specific level of scientific classification; below Genus
Sponge
Egg mass (in crustacean biology)
Stock
A population of individuals that are managed as a single unit within a fishery
Sustainable yield
Year-to-year, the number or weight of animals that can be harvested without reducing the stock
Swimmeret
Appendage on the abdomen; in crustaceans, females attach eggs to their swimmerets

Taxonomy
Classification and naming of organisms
TED
Turtle Excluder Device; device designed to allow turtles to escape from nets
Telson
Tail portion of a crustacean
Terminal molt
Final molt, usually at maturity, after which the animal no longer molts
Theory
Hypothesis that has substantial evidence to support it
Thorax
Central body part to which the walking legs are attached
Toxin
Poisonous substance produced by a living organism

Variable
Any factor that can change
Ventral
Toward the front of the body; opposite of dorsal

White sign
Blue crab that is 1-2 weeks from molting

Year class / Young-of-the-year
All individuals of a population spawned and hatched during a year; a generation or cohort

Zoea
Crab larva



FWC Facts:
Like a message in a bottle, “Please Release” on an external tag tells anglers that researchers are tracking a fish implanted with an acoustic tag.

Learn More at AskFWC