Rathbunaja ursus Ng & Forges 2015, n. sp.
Creators: name: Ng, Peter K. L.
name: Forges, Bertrand Richer De
Publisher: name: Zenodo
Year: 2015
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Majidae
Rathbunaja
Rathbunaja ursus

description: Rathbunaja ursus n. sp.   
(Figs. 60, 61G, H, 63E–H, 64E, F, 65H–K, 67A–D)  
 Material examined. Holotype: male (50.1 × 41.5 mm) (NMCR, ex ZRC 2013.1275), Balicasag Island, Panglao, Bohol, Philippines, 200–300 m, coll. fishermen with tangle nets, 2 March 2004. Paratypes: Philippines – 2 ovigerous females (46.8 × 36.6 mm, 45.0 × 36.0 mm) (ZRC 2001.0594), Balicasag Island, Panglao, Bohol, 200–300 m, coll. fishermen with tangle nets, 28 November 2001. — 1 male (41.6 × 32.8 mm), 1 ovigerous female (45.6 × 35.7 mm), 1 female (47.2 × 37.6 mm) (ZRC 2013.1276), Balicasag Island, Panglao, Bohol, 200–300 m, coll. fishermen with tangle nets, June 2002. — 1 female (49.4 × 38.4 mm) (NSMT-Cr 15386), Balicasag Island, Panglao, Bohol, coll. fishermen with tangle nets, via H. Komatsu & M. Takeda, February 2003. — 1 male (47.5 × 39.5 mm) (ZRC 2013.1277), Maribohoc Bay, Panglao, Bohol, coll. J. Arbasto, tangle nets, 30 May 2004.   
 Diagnosis. Carapace relatively broad (Fig. 60). Pseudorostral spines long, diverging (Fig. 60). Median row with 2 median gastric spines; 2 cardiac spines; 2 intestinal spines (Fig. 60). Basal antennal article with 2 relatively long distal spines, strongly diverging (Fig. 61G). Ischium of third maxilliped long (Fig. 63E–H). Ambulatory legs (notably merus and propodus) relatively long (Figs. 60, 65I–K). Male telson appears semicircular (Fig. 64E). G1 very long, strongly curved, slender, tip bent inwards (Fig. 67A–D).   
 Etymology. The name “ursus” alludes to the thick tomentum covering the animal like the fur of a bear, «ursus». The name is used as a noun in apposition.   
 Remarks. The discovery of Rathbunaja ursus n. sp. from Balicasag, Philippines, is rather surprising especially since there was also a specimen of R. bisarmata (Rathbun, 1916) collected from the same area. Most specimens of Rathbunaja from the Philippines actually belong to this new species. The two species are similar and are not easy to separate; In R. ursus, however, the carapace is relatively broader (Fig. 60 versus Fig. 59A, B), the two distal spines on the basal antennal article are more strongly diverging (Fig. 61G versus Fig. 61A, C), the ischium of the third maxilliped is proportionately longer (Fig. 63E–H versus Fig. 63A, B), the anterior thoracic sternum (sternites 1–4) is relatively longer (Fig. 64E, F versus Fig. 64A, B), the male telson is proportionately broader (Fig. 64E, F versus Fig. 64A, B), and the lateral margins of male abdominal somites 5 and 6 are more concave (Fig. 64E, F versus Fig. 64A, B). Most significantly, their G1 structures are completely different, with that of R. ursus much longer, with the distal part more strongly curved and slender (Fig. 67A–D versus Fig. 66A–G). These differences cannot be explained by size or maturity.
description: Published as part of 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, pp. 110-225 in Raffles Bulletin of Zoology 63 on page 216, DOI: 10.5281/zenodo.5384590