Blue Crab Taxonomy

Definitions

Superkingdom Eukaryota

The Eukaryota include the organisms that most people are most familiar with - all animals, plants, fungi, and protists. They also include the vast majority of the organisms that paleontologists work with. Although they show unbelievable diversity in form, they share fundamental characteristics of cellular organization, biochemistry, and molecular biology.

Kingdom Animalia

All animals are members of the Kingdom Animalia. This Kingdom does not contain the prokaryotes (Kingdom Monera, includes bacteria, blue-green algae) or the protists (Kingdom Protista, includes unicellular eukaryotic organisms). All members of the Animalia are multicellular, and all are heterotrophs (that is, they rely directly or indirectly on other organisms for their nourishment). Most ingest food and digest it in an internal cavity.

Animal cells lack the rigid cell walls that characterize plant cells. The bodies of most animals (all except sponges) are made up of cells organized into tissues, each tissue specialized to some degree to perform specific functions. In most, tissues are organized into even more specialized organs. Most animals are capable of complex and relatively rapid movement compared to plants and other organisms. Most reproduce sexually, by means of differentiated eggs and sperm. Most animals are diploid, meaning that the cells of adults contain two copies of the genetic material. The development of most animals is characterized by distinctive stages, including a zygote, formed by the product of the first few division of cells following fertilization; a blastula, which is a hollow ball of cells formed by the developing zygote; and a gastrula, which is formed when the blastula folds in on itself to form a double-walled structure with an opening to the outside, the blastopore.

Somewhere around 2 million species of animals inhabit the earth according to the World Animal Foundation; Animals range in size from no more than a few cells to organisms weighing many tons, such as blue whales and giant squid. Most animals inhabit the seas, with fewer in fresh water and even fewer on land.

Subkingdom Metazoa

Subkingdom of the animal kingdom comprising the multicellular animals in the traditional two-kingdom system of taxonomic classification, in which living organisms were considered to be either plants or animals. Metazoa included all animals except the protozoans, formerly classified as in the phylum Protozoa but now classified in the kingdom Protista. The term is still used informally.

Phylum Arthropoda

Arthropoda is the largest and most diverse animal phylum. It includes the trilobites, chelicerates, insects, and crustaceans. Arthropods have an exoskeleton that is molted periodically to accommodate growth. The body is segmented and the segments bear paired jointed appendages.

Subphylum Crustacea

Crustaceans are primarily aquatic arthropods. The crustacean head consists of five fused segments and bears five pairs of appendages including two pairs of antennae. Appendages are primitively biramous. Excretion and osmoregulation are via modified metanephridia known as end sac organs, respiration is via gills or a permeable body surface. The brain is tripartite. Compound eyes are frequently present.

Class Malacostraca

Malacostraca is a large group that includes the crabs, shrimps, and lobsters as well as several less familiar crustaceans, such as the peracarids. Malacostracans are relatively unspecialized crustaceans with appendages on the abdomen. The group is a large one and includes the largest crustaceans. The malacostracan body consists of head thorax, and abdomen, each with a characteristic number of segments. The head, like that of all crustaceans, consists of 5 fused segments. The thorax consists of 8, and the abdomen of 6. There is usually a carapace over some or all of the thorax and some anterior thoracic appendages are usually modified as maxillipeds.

Subclass Eumalacostraca

The Eumalacostraca (Greek word for "true soft shell") are a subclass of crustaceans, containing almost all living malacostracans, about 22,000 described species.

Eumalacostracans have 19 segments (5 cephalic, 8 thoracic, 6 abdominal.) The thoracic limbs are jointed and used for swimming or walking. The common ancestor is thought to have had a carapace, and most living species possess one, but it has been lost in some subgroups.

Superorder Eucarida

Eucarida is a superorder of crustaceans, comprising the decapods, krill and Amphionides. They are characterized by having the carapace fused to all thoracic segments, and by the possession of stalked eyes. Of all the groups of crustaceans, the Eucarida appeared relatively late in the fossil record. They first appear in the Mesozoic era, but are presumed to have first evolved much earlier.

Order Decapoda

The largest and most familiar crustaceans belong to the order Decapoda. The familiar crabs, shrimps, crayfishes, and lobsters are decapods. The first three segments of the decapod thorax are associated with the head and their appendages are maxillipeds. The remaining 5 thoracic appendages bear simple or chelate walking legs. The resulting five pairs of legs is the reason for the name decapod. The most primitive species (shrimps, lobsters, and crayfish) have well developed abdomens whereas the derived species (true crabs in the infraorder Brachura) have reduced, almost vestigial, abdomens.

Suborder Pleocyemata

Pleocyemata is a suborder of decapod crustaceans, erected by Martin Burkenroad in 1963. Burkenroad's classification replaced the earlier suborders of Natantia and Reptantia with the monophyletic groups Dendrobranchiata (prawns) and Pleocyemata. Pleocyemata contains all the members of the Reptantia (which is still used, but at a lower rank), as well as the Stenopodidea (which contains the so-called "boxer shrimp" or "barber-pole shrimp"), and Caridea, which contains all the true shrimp.

These taxa are united by a number of features, the most important of which is that the fertilized eggs are incubated by the female, and remain stuck to the pleopods (swimming legs) until they are ready to hatch. It is this characteristic that gives the group its name.

Infraorder Brachyura (True Crabs)

Brachyurans are the most advanced of the decapods in that they have the body most modified from the primitive shrimp-like decapod ancestor. The crab body is short, wide, and flat. The abdomen, once a muscular organ used for swimming, is now simply a flap used to cover reproductive appendages and hold eggs. The uropods, which along with the telson form the tailfan in other decapods, are totally absent in the crabs. In all but a few small groups all five pairs of walking legs are large. The first pair are always chelipeds. And the antennae and antennules are greatly reduced, and originate before the eyestalks.

Family Portunidae

Members of the family Portunidae are known as swimming crabs and are distinguished by the flattened paddle-like dactyl of the last leg, which allows them to swim in open water. All are very active and aggressive.

Authority Rathbun

Dr. Mary Jane Rathbun (January 11, 1860 - April 4, 1943). American marine zoologist known for establishing the basic taxonomic information on Crustacea. For many years she was the Smithsonian's complete department of marine invertebrates where she studied, cataloged, and preserved specimens. Through her basic studies and published works, she fixed the nomenclature of Crustacea and was the recognized, and the much sought after, authority in zoology and carcinology (the study of crustacea). When the department needed an assistant, she resigned as superintendent and used her salary to hire someone. She continued to work without pay as a dedicated volunteer carcinologist. She published over 160 papers on a wide variety of scientific subjects. The blue crab, Callinectes sapidus, was named by Dr. Rathbun.

Summary

Summary

Callinectes sapidus is a decapod crustacean of the family Portunidae, which includes the swimming crabs. It is easily identified by its body color which is generally a bright blue along the frontal area, especially along the chelipeds. The remainder of the body is shaded an olive brown color. As with other Portunids, the fifth leg is adapted to a paddle-like shape to accommodate swimming. Callinectes sapidus is sometimes confused with Callinectes similis and Callinectes ornatus, which are found in Florida.

For more information, see the National Center for Biotechnology Information (NCBI) Taxonomy Browser.