Rathbunaja, Ng & Forges, 2015

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 : 203-208

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/0598684B-FA6C-4BCB-81EB-289285178B6A

taxon LSID

lsid:zoobank.org:act:0598684B-FA6C-4BCB-81EB-289285178B6A

treatment provided by

Valdenar

scientific name

Rathbunaja
status

gen. nov.

Rathbunaja View in CoL n. gen.

Diagnosis. Carapace distinctly pyriform; dorsal surface covered by sharp granules, tubercles and short spines; gastric and branchial regions distinct, separated by distinct grooves; carapace and pereiopods covered with dense short setae, forming velvet-like pubescence ( Figs. 59 View Fig , 60 View Fig ). Cardiac region with 2 short spines arranged transversely; intestinal region with 2 or 3 short spines ( Figs. 59 View Fig , 60 View Fig ). Pseudorostral long or short, divergent ( Figs. 59 View Fig , 60 View Fig ). Supraorbital eave with anterior part longitudinally narrow, rectangular, not prominently expanded; antorbital spine short, directed laterally ( Figs. 59 View Fig , 60 View Fig , 62A View Fig ). Intercalated spine distinct, separated from supraorbital eave by wide keyhole shaped gap, separated from postorbital spine by narrow slit-like gap; postorbital spine strong; hepatic region with 1 strong spine, subequal or shorter than postorbital spine, surrounded by short spines and tubercles ( Figs. 59 View Fig , 60 View Fig , 62A View Fig ). Lateral carapace margin with 3 large spines and numerous spinules and tubercles around them; branchial region with 2 spines, outer one relatively larger ( Figs. 59 View Fig , 60 View Fig ). Posterior carapace margin always with 2 distinct median spines ( Figs. 59 View Fig , 60 View Fig ). Eyes relatively short, stout, with rounded cornea ( Figs. 61A, C, E, G View Fig , 62B View Fig ). Antennal flagellum long, slender ( Figs. 61A, C, E, G View Fig , 62B View Fig ). Basal antennal article longer than broad, with 2 long distal spines; proximal outer angle with small low tooth; inner and outer lateral margins entire; antero-external crested rim of antennular fossa slightly overlaps subdistal part of basal antennal article (61A, C, E, G, 62B). Epistome much wider than long, anterior margin with 2 low, flattened tubercles; posterior margin composed of 4 rectangular plates, lateral plates separated from median plates by deep fissures, median plate separated by shallow cleft (61A, C, E, G, 62B). Suborbital margin separated from basal antennal article by wide gap; suborbital tooth completely fused with postorbital tooth (61A, C, E, G, 62B). Outer surface of third maxilliped covered by short setae; ischium rectangular, smooth; postero-external angle of merus relatively broad, “inserted” into concavity on outer margin of ischium; antero-internal part of ischium rounded, relatively low, sub- or not auriculiform ( Figs. 62C View Fig , 63 View Fig ). Male chelipeds very long in adult males, surfaces of merus and carpus covered with distinct tubercles and granules; carpus elongate, with low granulated longitudinal ridge; palm elongated, curved, smooth, without lateral cristae, slightly enlarged, with swellings on dorsal and ventral margins in very large males; fingers long, slender, gently curved, with narrow basal gape when closed ( Figs. 59 View Fig , 60 View Fig , 65C, G, H View Fig ). Ambulatory leg merus with distinct distal spine on dorsal margin; dactylus relatively long, curved, covered with dense short and long setae except for corneous distal quarter ( Figs. 62D–G View Fig , 65B, D, F, I–K View Fig ). Thoracic sternum relatively wide; surfaces of somites 5–8 almost smooth; sternites 3 and 4 medially depressed; margin between sternites 2 and 3 demarcated by small notch; anterior margin of sterno-abdominal cavity forming incomplete rim with median part low ( Figs. 64 View Fig ). Male abdomen subrectangular, with 6 free somites and telson; telson subtriangular to semicircular, with convex margins ( Fig. 64 View Fig ). Male press-button abdominal locking mechanism submedian in position on sterno-abdominal cavity. Female abdomen dome-shaped, covering most of thoracic sternum. G1 very long, slender, curved distally, with subdistal dorsal flap (sometimes low), tip tapering, sharp; distal and subdistal surface with numerous short setae ( Figs. 66 View Fig , 67A–G View Fig ).

Comparative material. Leptomithrax longimanus ( Miers, 1876) – holotype male (38.0 × 36.2 mm) (NHM 1852.12), New Zealand, coll. R. Gunn. — 1 male (54.3 × 42.4 mm) (NIWA 6170), station KAH9704/127, 44°01.98’S 172°12.52’E, 31–34 m, New Zealand, coll. 5 January 1998. — 1 male (50.7 × 48.9 mm) (ZRC 2013.1617), Godley Head, east coast of South Island, New Zealand, in crab trap, coll. C. McLay, May 2003. Leptomithrax australis (Jacquinot, in Jacquinot & Lucas, 1853) – 1 male (77.9 × 68.9 mm), 1 female (47.0 × 39.2 mm) (ZRC 2013.1618), Banks Peninsula, east coast of South Island, New Zealand, 600 m, coll. C. L. McLay, May 2004. Leptomithrax longipes (G. M. Thomson, 1902) – 1 male (55.4 × 39.3 mm) (AM P86814), off Dunedin, New Zealand. — 1 male (39.8 × 39.3 mm) (ZRC 2013.1719, ex NIWA 42151), 1 female (45.7 × 36.7 mm) (ZRC 2013.1720 ex NIWA 44739), station KAH 0705/48, 44.4883°S 171.796°E – 44.5018°S 171.796°E, 63–65 m, New Zealand, coll. 18 May 2007. Leptomithrax waitei ( Whitelegge, 1900) – 1 male (29.9 × 23.7 mm), 1 female (23.5 × 17. 3 mm) (ZRC 2013.076, ex AM P64812), station K96-04-14, 32°52’S 152°02’E, Australia, coll. FRV Kapala , 13 March 1996. Leptomithrax edwardsii (De Haan, 1835) – 1 female (55.9 × 49.7 mm) (ZRC 2013.1186), Amakusa, Shikizuki, Kyushu, Japan, from fishermen, coll. J. Lai, September 2002. — 8 males (largest 69.8 × 62.8 mm), 7 females (ZRC 2013.1401), Amakusa, Tomioka Port, Kyushu, Japan, coll. J. Lai & S. Arakaki, 7–9 September 2002. — 1 male, 1 female (SMF 47751), None, Kochi Prefecture, ca. 33°26.617’N 134°16.75’E, Japan, coll. K. Matsuzawa, no other data. — 1 male (SMF 47754), None, Kochi Prefecture, ca. 33°26.617’N 134°16.75’E, Japan, coll. K. Matsuzawa, 11 December 1990. — 1 ovigerous female (SMF 47753), Toyocho, None, Muroto Cape, Kochi Prefecture, 33°26.617’N 134°16.75’E, Japan, coll. 12 June 1998. — 2 females (SMF 47756), None, Kochi Prefecture, ca. 33°26.617’N 134°16.75’E, Japan, coll. K. Matsuzawa, 24 March 1991. — 1 female (SMF 47755), None, Kochi Prefecture, ca. 33°26.617’N 134°16.75’E, Japan, coll. K. Matsuzawa, 18 May 1986. — 1 male (SMF 47740), Shikoku, Tosa Bay, Kochi Prefecture, 33°29.049’N 133°35.707’E, Japan, coll. 8 April 1988. — 1 male (SMF 47752), None, Cape Muroto, Kochi Prefecture, 33°26.617’N 134°16.75’E, Japan, coll. K. Matsuzawa, 18 November 1984. — 2 males, 1 female (SMF 47739), Tokushima, Shikoku, Ana, Tsubakidomari, Kochi Prefecture, 33°51.678’N 134°43.603’E, Japan, coll. K. Sakai, 19 April 1984. — 1 female (SMF 47809), None, west of cape Muroto, Kochi Prefecture, 33°26.617’N 134°16.75’E, Japan, coll. K. Matsuzawa, 12 June 1998. — 1 female (SMF 47727), Tosa Bay, near Mimase, Kochi Prefecture, 33°29.049’N 133°35.707’E, 150–200 m, Japan, coll. K. Sakai. — 2 males, 1 crushed juvenile (SMF 47735), Honshu, Wakayama Prefecture, Kii Minabe, 33°45.712’N 135°18.927’E, Japan, coll. K. Sakai, 1 March 1988. — 3 males (SMF 47731), Honshu, Wakayama Prefecture, Kii Minabe, 33°45.712’N 135°18.927’E, Japan, coll. K. Sakai, 26 October 1988. — 2 males (SMF 46528), Tsubaki Donarii, Anan City, Tokushina Prefecture, 33°50.62’N 134°42.75’E, Japan, coll. K. Sakai. — 1 female (SMF 47749), Japan, coll. K. Matsuzawa, 2005. — 1 dried male (SMF 47604), Japan, no other data, T. Sakai Collection. — 1 male (75.8 × 69.4 mm) (ZRC 2001.56), Tashi, Taiwan. Leptomithrax sinensis Rathbun, 1916 – holotype carapace (dried) (32.0 × 25.3 mm) (including spines, 38.3 × 28.8 mm) (USNM 48219), station 5311, South China Sea, near southern Luzon, 21°33’N 116°15’E, 88 fathoms, Philippines, coll. RV Albatross, 4 November 1908. Leptomithrax bifidus ( Ortmann, 1893) – 1 dried male (36.5 × 29.4 mm) (KPM NH4024), Kii-Nagashima, Japan, T. Sakai Collection, coll. March 1969. — 2 males (32.5 × 27.5 mm, 27.5 × 20.6 mm) (NHM 1961.11.13.28–29), Seto, Shirahama, Japan, coll. gill nets, I. Gordon & Harada, 1950s. — 2 males (ZRC), Mitsu, off Muroto Cape, Kochi Prefecture, Japan, 33°16.6’N 134°10.6’E, in coral nets, coll. 8 July 1988. — 1 male (with rhizocephala), 2 females (SMF 47758), Mitsu, off Muroto Cape, Kochi Prefecture, 33°16.6’N 134°10.6’E, in coral nets, Japan, coll. 21 June 1988. — 1 male, 1 female (SMF 47758), Mitsu, off Muroto Cape, Kochi Prefecture, 33°16.6’N 134°10.6’E, in coral nets, Japan, coll. 21 June 1988. — 1 male (SMF 47743), Tosa, Usa, Kochi Prefecture, 33°26.316’N 133°28.003’E, 160 m, Japan, coll. K. Sakai, 10 May 1990. — 5 males (SMF 47729), Honshu, Wakayama

Prefecture, Kii Mimase, 33°45.712’N 135°18.927’E, Japan GoogleMaps , coll. K. Sakai, 1 March 1988. Leptomithrax gaimardii (H. Milne Edwards, 1834) – 1 partially cracked female ( ZRC 1965.10.13.38), trawled off Disaster Bay , New South Wales, southern Australia , coll. M. Ward, 1930s. Leptomithrax sternocostulatus (H. Milne Edwards, 1851) – 1 male (35.1 × 27.0 mm), 1 ovigerous female (34.0 × 25.7 mm) ( ZRC 1965.10.13.74–75), Pittwater , New South Wales, southern Australia , coll. M. Ward, December 1932. Leptomithrax tuberculatus Whitelegge, 1900 – 1 female (36.6 × 28.7 mm) ( ZRC 1965.10.13.77), trawled off Newcastle , New South Wales, southeastern Australia , coll. M. Ward, 1930s. Leptomithrax eldredgei Richer de Forges & Ng, 2015 – holotype male (13.3 × 10.1 mm) ( ZRC 1970.2.17.1), 2 ovigerous paratype females (21.1 × 17.4 mm, 1 broken laterally), 1 paratype female (14.9 × 11.3 mm), 1 crushed paratype specimen ( ZRC 1970.2.17.2–5), Cr 2/63, station 24, T./10, Hong Kong , coll. & don. Fisheries Research Station of Hong Kong , 1967.

Type species. Maja bisarmata Rathbun, 1916 View in CoL , by present designation.

Etymology. The genus is named after Mary Jane Rathbun. The name is an arbitrary combination of her family name with Maja . Gender feminine.

Remarks. The position of the antennal flagellum, just outside the orbit, is diagnostic of Rathbunaja n. gen. ( Fig. 57G, H View Fig ). All other Leptomithrax species have the antennae positioned well outside the orbit ( Fig. 57A–F View Fig ) (see Griffin, 1966b; Griffin & Tranter, 1986). Leptomithrax Miers, 1876 , itself is a genus with 14 temperate to cold-water water species, mostly from the southern seas (see Griffin, 1966b; Griffin & Tranter, 1986; Richer de Forges, 1993; Ng et al., 2008). Northwestern Asia has four species, L. edwardsii (De Haan, 1835) , L. bifidus ( Ortmann, 1893) and L. sinensis Rathbun, 1916 , and L. kiiensis T. Sakai, 1969 ( Griffin, 1976; T. Sakai, 1976; Griffin & Tranter, 1986).

Bennett (1964) argued that three subgenera can be recognised in Leptomithrax Leptomithrax (Leptomithrax) s. str. (type species Paramithrax (Leptomithrax) longimanus Miers, 1876 ), Leptomithrax (Austromithrax) Bennett, 1964 (type species Leptomithrax (Austromithrax) mortenseni Bennett, 1964 ) and Leptomithrax (Zemithrax) Bennett, 1964 (type species Paramithrax longipes G. M. Thomson, 1902 ). As discussed at length by Griffin (1966b: 61), Bennett (1964) distinguished these subgenera on the basis of the position and structure of the basal antennal article and flagellum, form of the supraorbital margin, whether the region between the merus and ischium of the third maxilliped is swollen, and the presence or absence of depressions on the male thoracic sternum and/or abdomen. Griffin (1966b) argued that while some of the characters were useful, others appeared to be less reliable and varied between species. In addition, he was not certain about the placement of some species of Leptomithrax and was concerned that some of the groupings ended up with only a few species. As such, he preferred to recognise just one genus without subgenera for Leptomithrax . He maintained this stand in his revision of the Indo-West Pacific Majoidea ( Griffin & Tranter, 1986: 208), although he established a new monotypic genus, Teratomaia Griffin & Tranter, 1986 , for Leptomithrax richardsoni Dell, 1960 ; and transferred L. parvispinosus ( Ward, 1933) to a redefined Tumulosternum McCulloch, 1913 .

Looking at the published descriptions of the various Australian and New Zealand species, it is clear that there are at least three groups among the 11 species from this region. They correspond to Bennett’s (1964) three groupings well and these should eventually be recognised as distinct genera. Interestingly, McLay et al. (1995) conducted a cladistic analysis of the fossil and extant species of Leptomithrax , and recognised three groups of extant species which roughly correspond to Bennett’s (1964) subgenera. However, we defer from formally adopting Bennet’s subgenera as separate genera as this should only be done as part of a revision of the species of Leptomithrax . This is now being planned. It is nevertheless useful to provide a synopsis of the genus.

Leptomithrax s. str. contains L. longimanus ( Miers, 1876) (= Paramithrax (Leptomithrax) affinis Borradaile, 1916 ), L. australis (Jacquinot, in Jacquinot & Lucas, 1853) (= Paramithrax (Leptomithrax) brevirostris Miers, 1879 ), and L. garricki Griffin, 1966 . These species share the following suite of characters: the posterior carapace margin has two spines which may be short; the distal part of the basal antennal article is relatively short with the flagellum positioned just outside the orbit ( Fig. 57A View Fig ); the posterior edge of the supraorbital eave is well separated from the postorbital spine; the ischium of the third maxilliped is elongate and subrectangular with the antero-lateral angle unarmed ( Fig. 58A View Fig ); the pollex of the chela in large adult males forms a sharp angle with the rest of the palm; the surfaces of the male thoracic sternum and abdomen are level not distinctly depressed; and the male abdomen is subrectangular with the lateral margins subparallel.

A second group corresponding to Austromithrax contains L. mortenseni Bennett, 1964 , L. depressus Richer de Forges, 1993 , L. gaimardii (H. Milne Edwards, 1834) (= L. spinulosus Haswell, 1880 ; L. australiensis Miers, 1876 ), L. globifer Rathbun, 1918 , L. sternocostulatus (H. Milne Edwards, 1851) , L. tuberculatus Whitelegge, 1900 , and L. waitei ( Whitelegge, 1900) . They share the following characters: the posterior carapace margin has two spines; the distal part of the basal antennal article is relatively wide, with the flagellum positioned on the outer edge and far from the orbit ( Fig. 57B, C View Fig ); the posterior edge of the supraorbital eave is well separated from the postorbital spine; the ischium of the third maxilliped is relatively shorter, subrectangular to subtriangular, and the antero-lateral angle has a distinct spur or tooth ( Fig. 58B, C, E View Fig ); the pollex of the chela in large adult males is smoothly contiguous with the rest of the palm; the male thoracic sternum and abdomen may or may not have depressions; and the male abdomen is subtriangular with the lateral margins sloping towards the broader posterior part. On the basis of these characters, three of the northeastern Asian species ( L. edwardsii , L. bifidus , L. sinensis ) can be referred to Austromithrax (cf. Figs. 57D, E View Fig , 58D, F View Fig ). That said, this genus remains heterogeneous and the contained species should be revised to see if other natural groupings are apparent. Of these species, L. sinensis Rathbun, 1916 , may be a junior subjective synonym of L. bifidus ( Ortmann, 1893) . Richer de Forges & Ng (2015) discussed this matter at length when describing a new species, L. eldredgei , from Hong Kong and commented that the type of L. sinensis is just a carapace and only has short spines.

The third group corresponding to Zemithrax contains only L. longipes (G. M. Thomson, 1902) (= Leptomithrax (Zemithrax) molloch Bennett, 1964 ). Its defining suite of characters are as follow: the posterior carapace margin has only one spine or tooth; the posterior edge of the supraorbital eave and postorbital spine almost touch each other; the distal part of the basal antennal article is relatively narrow, with the flagellum positioned submedially and distant from the orbit ( Fig. 57F View Fig ); the ischium of the third maxilliped is relatively short, subtriangular with the distal part much wider than the proximal part, the anterolateral angle has a distinct tooth and the setal arrangement is very distinctive ( Fig. 58G, H View Fig ); the pollex of the chela in large adult males is smoothly contiguous with the rest of the palm; the male thoracic sternum and abdomen have distinct depressions; and the male abdomen is subtriangular with the lateral margins sloping towards the broader posterior part.

One of the characters used by Bennett (1964: 46, 53) to separate Zemithrax from the others was what he describes as a large boss (swelling) being present on the merus and ischium at the junction where they articulate. However, he admitted that while it was very obvious in the type species, L. longipes ( Fig. 58G, H View Fig ), it was also present but less distinct in other species, with L. globifer having the merus but not ischium swollen, while in L. gaimardi (as L. australiensis ), the ischium and merus are slightly swollen ( Bennett, 1964: 51). In the specimens on hand, the third maxilliped of L. tuberculatus has a small but distinct swelling only on the merus ( Fig. 58B View Fig ), whereas in L. sternocostulatus , the swelling is even smaller and less distinct ( Fig. 58C View Fig ). In L. bifidus , the swelling in the merus and ischium of the third maxilliped is very prominent ( Fig. 58F View Fig ), not unlike that described and figured for L. longipes (cf. Fig. 58G, H View Fig ; Bennett, 1964: figs. 50, 53). In addition, the shape of the ischium also appears to vary from being short with the proximal part much narrower than the distal part (e.g., L. tuberculatus ) ( Fig. 58B View Fig ) to being relatively longer with the difference in proportions less obvious (e.g., L. sternocostulatus , Fig. 58C View Fig ).

The northwestern Asian Leptomithrax kiiensis is very distinct from all other Leptomithrax and belongs to its own group, here named Rathbunaja n. gen. Rathbunaja is closest to Leptomithrax s. str. in the male thoracic sternum and abdomen not having any trace of depressions; the distal part of the basal antennal article is relatively short with the flagellum positioned just outside the orbit; the form of the third maxillipeds (ischium subrectangular without tooth or projection on antero-lateral angle of the ischium); the pollex of the chela in large adult males forms a sharp angle with the palm; and the subrectangular male abdomen with the lateral margins subparallel. However, Rathbunaja can easily be separated by the different carapace shape, being less inflated (notably in the branchial regions) with the pseudorostral and lateral spines proportionately longer ( Figs. 59 View Fig , 60 View Fig ); and having a prominent distal spine on the dorsal margin of the merus of the ambulatory leg ( Fig. 65B, D, F, I–K View Fig ) (absent in Leptomithrax s. str.).

ZRC

Zoological Reference Collection, National University of Singapore

T

Tavera, Department of Geology and Geophysics

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Decapoda

Family

Majidae

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