Biarctus sordidus Stimpson 1860

Biarctus sordidus (Stimpson, 1860)

(Fig. 2)

Arctus sordidus Stimpson 1860: 23 (type locality: Hong Kong).

Biarctus sordidus.— Holthuis 2002: 641, figs. 55–56.— Zhang & Liu 2006: 20, figs. 3, 4-3.—Chan 2010: 161.? Scyllarus martensii. — Nguyen 2010: 177, 181, fig. A. (in part). [not Pfeffer, 1881]

Material examined. Hsinchu, commerical trawler, 20 m, 17 Sep 1994, 1 female 19.0 mm cl (NMNS 003046- 00014); 28 Nov 1995, 20– 30 m, 3 females 17.5–21.0 mm cl (NMNS 003046-00013). Taichung City, Taichung harbor, commerical trawler, 20 m, 29 Oct 2004, 5 males 9.0–12.0 mm cl (NMNS 004610-00009); 0 5 Nov 2005, 3 females 10.5–16.4 mm cl. (NMNS 7147-013).

Diagnosis. Rostral, gastric and cardiac teeth elevated. Pregastric tooth absent. Orbital margin with 2 large teeth anteriorly and some weak tubercles posteriorly. Distinct transverse setose groove present between posterior margin of carapace and marginal groove. Medial incision at posterior margin of carapace not deep. Abdomen with arborescent sculpture, without elevated median dorsal carina. Posterior margins of abdominal tergites I–IV distinctly incised medially. Abdominal pleura II–V ventrally rounded. Anterior margin of antennal segment VI bearing 4 distinct teeth with round tips. Antennal segment IV lacking additional carina, anterior margin bearing 4 or 5 teeth and with innermost one largest, outer margin having 2 teeth. Dactylus of pereiopod II longest in all pereiopods, more or less twice as long as that of pereiopod IV. Anterior end of thoracic sternum with a deep triangular “V”-shaped incision. Thoracic sternite I–V without median tubercle.

Coloration. Coloration of the Taiwanese material was not recorded and only a large median dark spot is still present on the abdominal tergite I in the preserved specimens (also see Holthuis 2002). The coloration of this species is described by Chhapgar & Deshmukh (1964) as “Colour muddy grey: there is a prominent dark red oval spot (fading to black on preservation) in the middle of the first abdominal segment”. A color photograph of B. sordidus (as Scyllarus sordidus) was published by Mutchacheep (1992).

Distribution. Widely distributed in the Indo-West Pacific from the Persian Gulf to southern China, Taiwan and Australia; at depths of 2.7 to about 40 m.

Remarks. Biarctus sordidus is the most widely distributed species of the four species in the genus (Holthuis 2002). Previously only one Biarctus species was reported from Taiwan and it is B. vitiensis (Dana, 1852) (as Scyllarus longidactylus in Chan & Yu 1986, 1993). Biarctus sordidus is readily distinguished from B. vitiensis in having a highly elevated cardiac tooth (as high as gastric tooth vs. much lower than gastric tooth in B. vitiensis). A recently published photograph on Eduarctus martensii (Pfeffer, 1881) from Vietnam (Nguyen 2010: fig. A. as “ Scyllarus martensii Pfeffer, 1881?”) showed two preserved specimens, one in dorsal view and one in ventral view. Neither specimen is E. martensii. The specimen in dorsal view on the right is B. sordidus and the ventral view specimen on the left is Remiarctus bertholdii (Paulson, 1875). Biarctus sordidus is also now recorded from Vietnam and it seems to be rather common there (personal observation).