Callinectes similis is a good swimmer, and its last pereiopods are expanded to paddles with which it swims. Adult males may grow up to a width of 122 millimetres (4.8 in), while females may reach 95 mm (3.7 in).[3]
Callinectes similis is most closely related to Callinectes danae,[4] a species also found in the Gulf of Mexico, but whose range extends as far south as Rio Grande do Sul,[5] and C. ornatus, a species found from North Carolina to Rio Grande do Sul.[6]C. similis is most easily separated from C. danae and C. ornatus by the form of the first and second pleopods in males.[7] It can be told apart from the more distantly related C. sapidus by the number of teeth on the front edge of the carapace, there being six in C. similis and only four in C. sapidus.[7]
Callinectes similis lives in marshes and estuaries, being the dominant crab in open bays. The species is limited to salinities of at least 15‰, and temperature may also affect reproduction.[3]
Spawning takes place in the spring and fall, with females returning to estuaries to release their eggs.[3] Ovigerous (egg-carrying) females carry an average of more than 250,000 eggs.[2]
^ abcSergio Chazaro-Olvera; Arturo Rocha-Ramirez; Ramiro Roman-Contreras (2000). "Observations on feeding, maturity and fecundity of Callinectes similis Williams, 1966, on the central continental shelf off Veracruz, Gulf of Mexico". Crustaceana. 73 (3): 323–332. doi:10.1163/156854000504417.
^Rafael Robles; Christoph D. Schubart; Jesús E. Conde; Carlos Carmona-Suárez; Fernando Alvarez; José L. Villalobos; Darryl L. Felder (2007). "Molecular phylogeny of the American Callinectes Stimpson, 1860 (Brachyura: Portunidae), based on two partial mitochondrial genes". Marine Biology. 150 (6): 1265–1274. doi:10.1007/s00227-006-0437-7. S2CID84807146.
