Cambarus gentryi, the linear cobalt crayfish,^[2] is a small species of burrowing crayfish. One of 115 species in the genus Cambarus,^[3] it is notable for its deep blue carapace.^[4] It is endemic to Tennessee in the United States.^[1][2]

Quick Facts Cambarus gentryi, Conservation status ...

Cambarus gentryi
Conservation status
Least Concern  (IUCN 3.1)[1]
Apparently Secure  (NatureServe)[2]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Arthropoda
Class:	Malacostraca
Order:	Decapoda
Suborder:	Pleocyemata
Family:	Cambaridae
Genus:	Cambarus
Species:	C. gentryi
Binomial name
Cambarus gentryi Hobbs, 1970

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Although three specimens of C. gentryi were collected and stored in the 1890s, the species was not described until 1970 by Horton Hobbs Jr.^[5] This followed its 1968 collection by Dr. Glenn Gentry, from which the species name was derived.^[5]

The linear cobalt crayfish has been found in the Cumberland and Duck river basins in Tennessee.^[4]There are 37 reported sightings of C. gentryi on the Global Biodiversity Information Facility (GBIF) between 1962-2022.^[6] They are all localized to the southern part of Tennessee in the USA, North America.^[6]

Cambarus gentryi has a shell length of around 3–5 cm (1.2–2.0 in) and pincers about 2 cm (0.79 in) long.^[4] Its shell is cobalt blue in colour with orange or yellow to yellowish-green markings.^[4] The eyes are small and well-developed, and the areola (a structure which runs along the centre of the cephalothorax) is sublinear, or mostly uncurved.^[5] Like other decapods, C. gentryi has ten pairs of legs, of which the forward-most pair are modified into robust pincers known as chela.^[7] A detailed description of the morphological identifiers unique to C. gentryi, alongside drawings of the type specimen, may be found in the original species description in the Biodiversity Heritage Library: https://www.biodiversitylibrary.org/page/34572783.^[5]

The type specimen is stored in the Smithsonian Institute in Washington, D.C., USA under the identifier USNM 130283.^[8] The allotype (female) and morphotype (male) are in the same institution under the identifiers USNM 130284 and 130285.^[8]

The linear cobalt crayfish creates burrows in damp areas along river banks.^[5] Its burrows have been described in several locations across its range; although sometimes limited by soil depth, they can have multiple openings to the surface and have been found to be up to about 2.5 m (8 ft) in length and 0.91 m (3 ft) in depth.^[5][8]

Adults in family Cambaridae alternate molts between reproductive (form I) and non reproductive (Form II) forms.^[7] Male form I has larger claws and altered sperm transfer gonopods; in some species, the female form I has a wider abdomen.^[7] On collection of C. gentryi specimens in and prior to 1970, first-form males were collected at various times of year (April, May, and November) and egg- or young-bearing females had not been collected or identified.^[5]

The exact lifespan of C. gentryi is not known; however, other individuals in this family (Cambaridae) have been known to live 6-7 years.^[7]

C. gentryi is a known host of Uncinocythere zancla, an entocytherid osctracod.^[9] This is a small crustacean which lives as an obligate ectosymbiont to other crustaceans by attaching to the carapaces.^[10]

Cambarus gentryi is listed as least concern by the IUCN.^[1]

Five publicly available gene fragment sequences exist for C. gentryi, available through NCBI genbank with taxonomy ID NCBI:txid318489.^[11] The following gene fragments are available:^[11]

1. Isolate JF2508 cytochrome c oxidase subunit I (COI) gene; Accession no. KX417101.1
2. Histone H3 (H3) gene, partial cds; Accession no. DQ411804.1
3. Cytochrome oxidase subunit I (CO1) gene, partial cds; mitochondrial; Accession no. DQ411785.1
4. 12S ribosomal RNA gene, partial sequence; mitochondrial; Accession no. DQ411731.1
5. 16S ribosomal RNA gene, partial sequence; mitochondrial; Accession no. AY853664.1