Rathbunaja bisarmata ( Rathbun, 1916 )

Ng, Peter K. L. & Forges, Bertrand Richer De, 2015, Revision of the spider crab genus Maja Lamarck, 1801 (Crustacea: Brachyura: Majoidea: Majidae), with descriptions of seven new genera and 17 new species from the Atlantic and Indo-West Pacific, Raffles Bulletin of Zoology 63, pp. 110-225 : 211-212

publication ID	https://doi.org/ 10.5281/zenodo.5384590
publication LSID	lsid:zoobank.org:pub:40BCDD62-D35E-46D1-95A3-2CC0DF219DEE
persistent identifier	https://treatment.plazi.org/id/03A9654B-FFE4-073E-578E-FF3F7803FC36
treatment provided by	Valdenar
scientific name	Rathbunaja bisarmata ( Rathbun, 1916 )
status

Treatment

Rathbunaja bisarmata ( Rathbun, 1916) View in CoL

( Figs. 59A, B View Fig , 61A–D View Fig , 63A, B View Fig , 64A, B View Fig , 65A–D View Fig , 66A–G View Fig )

Maja bisarmata Rathbun, 1916: 553 View in CoL . – Serène, 1968: 57. – Griffin, 1976: 199, Fig. 7b View Fig . – Griffin & Tranter, 1986: 211 (key).

Material examined. Holotype: male (20.3 × 15.6 mm) ( USNM 48220 About USNM ), station 5519, Point Tagolo Light, off northern Mindanao, 80°47’N 123°31.25’E, Philippines, coll. RV Albatross , 9 August 1909. Others : Philippines – 1 male (37.1 × 29.6 mm) ( ZRC 2013.1274 View Materials ), Balicasag Island , Panglao , Bohol, 200–300 m, coll. fishermen with tangle nets, 2 March 2004. GoogleMaps

Diagnosis. Carapace relatively narrow ( Fig. 59A, B View Fig ). Pseudorostral spines long, diverging ( Fig. 59A, B View Fig ). Median row with 2 median gastric spines; 2 cardiac spines; 2 intestinal spines ( Fig. 59A, B View Fig ). Basal antennal article with 2 relatively short distal spines not strongly diverging ( Fig. 61A–D View Fig ). Ischium of third maxilliped proportionately shorter ( Fig. 63A, B View Fig ). Ambulatory merus relatively shorter, stouter ( Figs. View Fig

59A, B, 65B, D View Fig ). Male telson subtriangular ( Fig. 64A, B View Fig ). G1 gently curved, distal part relatively shorter ( Fig. 66A–G View Fig ).

Remarks. This is a very poorly known species and although it has been treated as a valid Maja species by Griffin (1976) (who examined the type) and Griffin & Tranter (1986), a re-examination of the holotype shows otherwise. Although Rathbun (1916) placed this species in Maja , its antennal flagellum is actually just outside the orbit. In fact, the species is very close to Leptomithrax kiiensis , described by T. Sakai (1969) on the basis of a large male 55.0 by 44.5 mm from Kii Minable in Japan. Tune Sakai (1969, 1976) placed this species in Leptomithrax because its antennal flagellum is just outside the orbit, even if it is not to the same degree as other congeners.

The holotype male of Maja bisarmata is relatively small ( Fig. 59A View Fig ) and although its G1 is not fully developed ( Fig. 61A–D View Fig ), it shows enough features. A recent larger specimen from the Philippines agrees well with the type male in its carapace form, antennal basal article, epistome, structure of the third maxilliped, relatively short ambulatory legs, thoracic sternum, male abdomen and structure of the G1, and we are confident they are conspecific. These features make it unlikely that Maja bisarmata is the juvenile form of the more common new species described here from the Philippines, Rathbunaja ursus .

Maja bisarmata Rathbun, 1916 , is very close to Leptomithrax kiiensis T. Sakai, 1969 . Comparisons of Rathbun’s species with material of L. kiiensis from Japan as well as the descriptions and figures of the species by T. Sakai (1969, 1976), Miyake (1983) and Ikeda (1998) show minimal differences. The main difference appears to be the relative lengths of the merus of the ambulatory leg, which in R. kiiensis , is proportionately longer and more slender ( Figs. 59C, E View Fig , 65F View Fig ) than that of R. bisarmata ( Figs. 59A, B View Fig , 65B, D View Fig ). The distal part of the G1 of R. kiiensis is more curved and slightly longer than that of R. bisarmata ( Fig. 66H–M View Fig versus Fig. 66A–G View Fig ). As such, both species are recognised for the time being. As discussed under the genus, the distinctive features of these two species (as well as two other new ones here described) warrant the establishment of a new genus, Rathbunaja , for them.