Orisarma magnum ( Komai & Ng, 2013 )

Schubart, Christoph D. & Ng, Peter K. L., 2020, Revision of the intertidal and semiterrestrial crab genera Chiromantes Gistel, 1848, and Pseudosesarma Serène & Soh, 1970 (Crustacea: Brachyura: Sesarmidae), using morphology and molecular phylogenetics, with the establishment of nine new genera and two new species, Raffles Bulletin of Zoology 68, pp. 891-994 : 910-912

publication ID

https://doi.org/ 10.26107/RBZ-2020-0097

publication LSID

lsid:zoobank.org:pub:815E4670-B063-4FD8-B31E-3AD89B3A7942

DOI

https://doi.org/10.5281/zenodo.6532421

persistent identifier

https://treatment.plazi.org/id/49152B56-FFF2-BA34-FC55-F9AEFBCDFEE4

treatment provided by

Diego

scientific name

Orisarma magnum ( Komai & Ng, 2013 )
status

 

Orisarma magnum ( Komai & Ng, 2013) View in CoL

( Figs. 1F View Fig , 11M–P View Fig )

Sesarma dehaani View in CoL – Stimpson, 1858: 106 (part); Stimpson, 1907: 134 (part); Parisi, 1918: 111 (part); Asakura et al., 1993: 10.

Holometopus dehaani – Takeda & Miyake, 1976: 113 (list).

Sesarma (Holometopus) dehaani View in CoL – Ooishi, 1970: 95.

Chiromantes dehaani View in CoL – Marumura & Kosaka, 2003: 66 (part); Takeda & Ueshima, 2006: 93 (part); Komatsu, 2011: 277 (list).

Chiromantes magnus Komai & Ng, 2013: 539 View in CoL View Cited Treatment , figs. 1A, 2–5; Toyota & Seki, 2014: 191.

Material examined. Holotype: male (52.2 × 47.2 mm) ( CBM-ZC 11452 ), Renju Valley , Chichi-jima Island, Ogasawara Islands, coll. H. Tachikawa, 23 September 2008. Paratypes: 1 male (50.1 × 44.4 mm) ( CBM-ZC 11456 ), 1 male (50.6 × 45.6 mm) ( ZRC 2013.0173 View Materials ), same data as holotype ; 1 male (41.8 × 37.9 mm) ( CBM-ZC 11453 ), Kominato , Chichi-jima Island, coll. T. Komai, 10 December 2005 ; 1 male (28.2 × 25.5 mm) ( CBM-ZC 11454 ), Kopepe Beach , Chichi-jima Island, coll. T. Komai, 11 December 2005 ; 1 male (45.2 × 40.8 mm) ( RUMF-ZC 2160 ), same locality, coll. Y. Fujita, 22 June 2010 ; 1 ovigerous female (43.5 × 40.2 mm) ( RUMF-ZC 2362 ), same data as above ; 1 male (49.8 × 44.0 mm) ( RUMF-ZC 2360 ), same locality as above, coll. Y. Fujita, 27 June 2010 ; 4 males (smallest 18.2 × 15.8 mm, largest 28.5 × 26.1 mm), 1 female (27.9 × 25.2 mm), CBM-ZC 11455, Chichi-jima Island , coll. K. Iwasaki et al., August 2008 ; 1 male (50.3 × 45.5 mm) ( CBM-ZC 11457 ), Okumura River , river mouth, coll. H. Tachikawa, 28 September 2008 ; 1 female ( CBM-ZC 11600 ), Kiyose , Chichi-jima Island, coll. T. Komai, 14 July 2009 ; 1 male (28.3 × 25.3 mm) ( RUMF-ZC 2361 ), same locality as above, coll. Y. Fujita, 25 June 2010 .

Diagnosis. Carapace subquadrate; lateral margin entire, no trace of epibranchial tooth; posterolateral margins gently diverging towards posterior carapace margin; dorsal surface relatively lower, gastric region less swollen, grooves separating regions deep, prominent; frontal lobes separated by deep, broad concavity; ambulatory merus relatively long; chitinous part of G1 evenly cylindrical. In life, carapace with mottled pattern of black-brown and gray-brown or yellowish gray; chelae light olive or yellowish gray.

Colour. Komai & Ng (2013: 547) noted that in life “the carapace has a mottled pattern of black-brown and gray-brown or yellowish gray with scattered whitish spots; the carpus and the dorsal part of chela are light olive or yellowish gray; striae on the ambulatory meri are dark brown”.

Remarks. The taxonomy of this species was treated at length by Komai & Ng (2013). The main differences between O. magnum and the related O. dehaani and O. neglectum (other than its much larger adult size) are gently diverging posterolateral margins which give it a more subtrapezoidal appearance ( Fig. 1F View Fig ) and the proportionately longer and more slender ambulatory meri ( Fig. 1F View Fig ). Their colours in life also differ, with that of O. magnum being unusually mottled.

In the current genetic dataset, there are no obvious genetic differences between O. magnum , O. neglectum , and O. dehaani , which should normally be expected for intraspecific relationships. We see a similar pattern for the closely related O. intermedium and O. sinense . The morphological differences, however, are such that all three of them must be recognised as distinct species. The relative gigantism of O. magnum may be due to the effects of island life as the Ogasawara Islands are very isolated and over 1000 km away from mainland Japan, but this is probably not enough to explain its much larger size.

Biology. Komai & Ng (2013: 547) comment that “Individuals occur in estuarine areas to middle parts of rivers or streams where tidal influence is completely absent, sometimes extending to adjacent marsh areas, and sometimes found in burrows under rocks”. This is not dissimilar to O. dehaani which has also been found some distance from the sea. Nevertheless, the water table (which they can reach through their burrows) is probably still at least brackish in content.

Distribution. Known only from the Ogasawara Islands thus far ( Komai & Ng, 2013).

Kingdom

Animalia

Phylum

Arthropoda

Class

Malacostraca

Order

Decapoda

InfraOrder

Brachyura

Family

Sesarmidae

Genus

Orisarma

Loc

Orisarma magnum ( Komai & Ng, 2013 )

Schubart, Christoph D. & Ng, Peter K. L. 2020
2020
Loc

Chiromantes magnus

Toyota K & Seki S 2014: 191
Komai T & Ng PKL 2013: 539
2013
Loc

Chiromantes dehaani

Komatsu H 2011: 277
Takeda M & Ueshima R 2006: 93
Marumura M & Kosaka A 2003: 66
2003
Loc

Holometopus dehaani

Takeda M & Miyake S 1976: 113
1976
Loc

Sesarma (Holometopus) dehaani

Ooishi S 1970: 95
1970
Loc

Sesarma dehaani

Asakura A, Nishihama S & Kondo Y 1993: 10
Parisi B 1918: 111
Stimpson W 1907: 134
Stimpson W 1858: 106
1858
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