Geosesarma bicolor
Geosesarma bicolor:
Geosesarma bicolor Ng & Davie, 1995 is a terrestrial freshwater sesarmid crab endemic to Ujung Kulon, West Java, Indonesia (Ng & Davies, 1995). There are quite a few crabs sold under the name of Geosesarma bicolor but it is doubtful based on the taxonomic description that any of those crabs are G. bicolor. The TGD team have compared known photos of this species sold under this name and none match the distinctive color pattern of this species and should be listed as Geosesarma aff. bicolor on labels. All those that are sold under different common names such as “Marble”, “Red Arm”, “Golden Eye”, “Halloween”, etc. for G. bicolor should be treated as separate species and kept in separate containers. As it stands G. bicolor is a sort of wastebasket taxonomic placement for non-easily identified Geosesarma spp. in the hobby and should be taken with caution.
The TGD Team hopes we will be able to compare identifying features of these misidentified species with the taxonomic description features and sort out this mislabeling on species under the Geosesarma bicolor name.
Geosesarma bicolor is visually with the anterior ⅓ of the carapace as well as the ambulatory legs being a dark, to sometimes bright, purplish to purple-blue with the posterior ⅔ of the carapace being a lighter grayish-blue. In contrast the eyes are a vibrant yellow with the chelae being red (indonesian land crabs, 2021; Ng & Davie, 1995; Ng, Schubart, & Lukhaup, 2015).
Size of Geosesarma bicolor
Adult males of this species were described by Ng & Davies (1995) as ranging between the holotype being 11.0 x 10.5mm and 10.5 x9.9mm, holotype, and two non-ovigerous (non-eggbearing) mature females ranging between 13.9 x 12.7mm and 10.0 x 9.7mm from the same location as holotype (Ng & Davies, 1995).
Habitat of Geosesarma bicolor
(G. bicolor was found in the wild by Indonesia land crabs (2021) in just barely trickling spring fed creek beds where the stream bank walls as well as the surrounding soil was composed of a high percentage of clay in the soil. The banks of the creek bed were around 1-1.5 meters high will juvenile and adults being found in excavated burrows perpendicular to the creek bed and that were elevated off of the creek bed by around 2-3ft. Burrows were found with regularity in close proximity to another but with only one individual occupying any single burrow at a time. G. bicolor was also found under stones at the creekbed (Ng & Davies, 1995).
Due to this physical observation of the life habit of G. bicolor the territoriality of males may stem not from their aggression towards each other as a general rule but from having a lack of dedicated personal territories to burrow into off of the floor of a vivarium, like the above mentioned creekwall burrows.
Below is a video of Geosesarma cf. bicolor in situ in Indonesia.
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References:
WoRMS (2022). Geosesarma bicolor Ng & Davie, 1995. Accessed at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=444525 on 2022-11-19
Ng, P, K, L., & Davie, P, J, F. (1995). The Terrestrail Searmine Crabs of The Genera Metasesarma And Geosesarma (Crustacea: Decapoda: Brachyura: Graspidae) Of Ujung Kulon, West Jawa, Indonesia. Tropical Biodiversity, 3(1), 29-43. https://www.researchgate.net/publication/270587668
Indonesian Land Crabs. (2021). habitat asli vampire ccrab .(original habitat of geocesarma golden eye). Youtube Video. https://www.youtube.com/watch?v=w1iBdW3MnB4
Ng, P, K, L., Sschubart, C, D., & Lukhaup, C. (2018). New species of “vampire crabs” (Geosesarma De Man, 1892) from central Java, Indonesia, and the identity of Sesarma (Geosesarma) nodulifera De Man, 1892 (Crustacea, Brachyura, Thoracotremata, Sesarmidae). Raffles Bulletin of Zoology, 63, 3-13. http://zoobank.org/urn:lsid:zoobank.org:pub:9F76CF88-A3DD-4F0E-B348-EEB9558DBBC4