Bathyarctus chani, Holthuis, 2002

Holthuis, Lipke B., 2002, The Indo-Pacific scyllarine lobsters (Crustacea, Decapoda, Scyllaridae), Zoosystema 24 (3), pp. 499-683 : 511-515

Bathyarctus chani n. sp.

( Figs 4 ; 5 ; 66C )

TYPE MATERIAL. — Holotype: CHALCAL 2, stn CC 1, 22 mm (MNHN-Pa 1884); paratypes: Su-Aou, 1 20 mm, 1 20 mm ( RMNH D 49554).

TYPE LOCALITY. — South of New Caledonia, 24°54.96’S, 168°21.91’E, 500- 580 m.

MATERIAL EXAMINED. — South of New Caledonia. CHALCAL 2, stn CC1, 24°54.96’S, 168°21.91’E, 500-580 m, 28.X.1986, 1 holotype 22 mm (MNHN-Pa 1884).

Taiwan. NE Coast, Su-Aou fishing port, I-Lan County, depth about 500 m, 17.VI.1993, T. Y. Chan leg., 1 paratype 20 mm, 1 paratype 20 mm ; don. National Taiwan Ocean University ( RMNH D 49554) .

DISTRIBUTION AND HABITAT. — At present the species is only known from NE Taiwan and New Caledonia. The Taiwan material was taken at a depth of about 500 m, that of New Caledonia at 500- 580 m.

ETYMOLOGY. — The species is named for Dr Tin-Yam Chan, who pointed out to me the differences between this species and B. formosanus .

DESCRIPTION

The rostrum bears a rather large single rounded tubercle and is only slightly constricted behind the top; it bears a low and blunt dorsal ridge with a few inconspicuous tubercles; but there is no true rostral tooth. The pregastric tooth is broad and blunt, with a distinct but very small double tubercle on its posterior slope. The gastric tooth is distinctly larger than the pregastric and has a broadly rounded top; its posterior slope shows two or three rows of two or three squamiform tubercles; these rows extend to the cervical groove. The cardiac tooth reaches over the cervical groove and is rounded or two-topped; its top is followed by two submedian rows of five to nine squamiform tubercles. These two rows of submedian tubercles are sharp and straight and separated by an equally straight and clearly defined median groove. A divergent row of three tubercles is placed next to the anterior part of the submedian carinae. The anterior branchial carina ends anteriorly in two low blunt teeth, the posterior of which is the larger; the anterior being a mere tubercle placed below the posterior tooth. These teeth are placed on the inner part of the orbital margin, the rest of the anterior branchial carina is sharp, high and smooth. The lower margin of the orbit shows about three small tubercles. The anterior and posterior branchial carinae are separated by a very wide gap formed by the cervical groove; a sometimes indistinct tubercle is placed within or slightly outside the gap. The posterior branchial carina is high and carries six to eight squamiform tubercles of various sizes. The area between the anterior postrostral carina and the anterior branchial carina shows small rounded tubercles in a rather narrow field along the anterior margin of the carapace. Just behind this field and nearer to the branchial carina is a pair of larger tubercles, probably representing the anterior submedian carina; at each side of the gastric tooth there is an oblique, diverging row of two or three similar tubercles. Between the posterior postrostral and posterior branchial ridges there is a distinct row of five or six intermediate tubercles, while two additional tubercles are placed between the intermediate row and the tip of the posterior branchial carina. The posterior submedian carina is short and carries two or three rounded tubercles; a few additional tubercles may be present.

The posterior orbital margin is smooth, merges at the inner end with the anterior branchial carina, and externally ends in a blunt tubercle. The anterior margin of the orbit shows three large tubercles. The postorbital surface is smooth but for a distinct single postorbital tubercle, which may be elongate in shape. The intercervical area is somewhat elevated and consists of a slightly curved row of closely placed tubercles.

The lateral margin of the carapace has four anterolateral teeth (the anterior of which is largest), two mediolateral teeth (the posterior being quite small), and seven posterolateral teeth.

The posterior margin of the postcervical groove between the branchial and lateral carinae bears a row of three or four blunt tubercles. A row of six to eight tubercles is placed against the posterior lateral carina, which thereby gives the impression of carrying a double row of tubercles. More tubercles fill the posterior part of the area between posterior branchial and posterior lateral carinae, and extend along the anterior part of the posterior branchial carina.

The posterior margin of the carapace shows a blunt and wide median incision. A row of about 12 large, rounded tubercles and a few scattered small ones extends along the posterior margin. Before these tubercles is the rather wide and deep marginal groove. Before the marginal groove are two transverse rows of tubercles, the anterior row consists of 12 large, and the posterior of about 12 small, more irregularly arranged tubercles.

The first abdominal somite shows a transverse groove, behind which extends a row of about 20 tubercles, some double. Abdominal somites II to V have a median longitudinal carina, which are of about the same height, or those of somites II and III are slightly lower than the others; the carinae of somites II to IV show a sharp median groove. The carinae are rather faintly lobulated laterally. Behind the transverse groove on the tergum of each half of somites II to IV there is a row of about seven tubercles of about equal size, some near the median carinae may be double. Before the transverse groove there are tubercles that form two groups separated by a deep oblique groove; each group of tubercles is flattened and forms a plateau-like figure, the outer group being larger than the inner. The smooth anterior half of the abdominal somites shows no hairy groove, but there are a few irregular pits.

The lateral margin of the pleura of the first abdominal somite bears three tubercles. The pleuron of the second somite shows a wide X-shaped groove, a rather long row of tubercles behind it, and some larger tubercles elsewhere. The anterior margin of pleuron II has a conspicuous basal lobe with some blunt tubercles, the rest of the margin is smooth with some low tubercles behind it. The posterior margin shows a blunt incision behind the apex, above which is a row of tubercles diminishing in size dorsally. The pleura of the third and fourth somites have the anterior half flat with a smooth anterior margin; the posterior half shows two parallel rows of tubercles separated by a deep groove and with the posterior margin bluntly serrate. Somites I to IV show a distinct median incision in the posterior margin. The fifth abdominal somite has a distinct median longitudinal carina. The lateral surface and the pleura is as in somites III and IV, only the posterior margin of the pleura shows a blunt tooth in the middle. The upper surface of the sixth somite has three transverse rows of large tubercles; these rows are of different length; the anterior is interrupted in the middle. The firm part of the telson is provided with six longitudinal carinae: 1) two lateral carinae are placed on the lateral margin, they carry squamiform tubercles; 2) two submedian carinae, that are the shortest; and 3) a pair of intermediate carinae between the lateral and submedian carinae. A flat tubercle is placed between the posterior ends of the lateral and intermediate carinae.

The anterior margin of the antennular somite is incised in the middle and bears a blunt tooth in each half.

The sixth (last) antennal segment ends in seven rather slender teeth with blunt tops; one of the seven is placed on the inner margin of the segment. The upper surface of the segment bears several small rounded tubercles. The fifth segment shows three blunt teeth on the anterior margin; the inner of these is the strongest and forms the end of a rather high carina. The fourth segment ends in a blunt tooth which forms the end of a curved oblique carina, which traverses the full length of the segment; this carina has a few distinct tubercles in the basal part, the rest is smooth. A second, shorter, parallel carina is seen on the outer half of the segment; it bears a row of small but distinct tubercles. On the base of the segment one or two high blunt teeth are present. The anterior margin shows a distinct blunt tooth just before the middle; between this tooth and the base of the margin three very small teeth are visible, and between the large tooth and the tip of the segment there are six similar small teeth. The outer margin of the segment has four or five teeth, the proximal two or three being indistinct. A few small round tubercles are visible on the upper surface of the segment. The third segment shows two large blunt teeth on the inner part of the anterior margin and some small tubercles on the rest of the surface.

The anterior margin of the epistome is incised in the middle and sharply angular at either lateral end.

P.1 is relatively slender. The propodus is 2.5 times as long as the dactylus and about twice as long as high. The dactylus shows a few hairs in the basal part of the upper margin. The lower margin bears a fringe of setae. The posterior surface of the merus has a longitudinal hairy groove in the upper half and some hairy depressions in the lower; hairs are also present on the lower margin. The dactylus of P.2 is longer than any of the other dactyli, it is two thirds as long as the propodus, which is about four times as long as high. Like in P.1 the dorsal margin of the dactylus shows some hairs in the basal part. The propodus of P.2 has a fringe of ventral hairs and some short hairs on the rest of the surface. The merus of P.2 to P.4 has both a dorsal and a ventral fringe of hairs, and a longitudinal hairy groove in the upper part of the posterior surface, the lower half has small irregular hairy depressions. The dactylus of P.3 and P.4 has a dorsal fringe of hairs and also some hairs on the lower margin. The propodus of these two legs is rather shaggy with dorsal and ventral hair fringes, and short hairs inbetween. Hairs are also visible in the dorsal part of the carpus. The fifth leg has dorsal hairs on propodus, carpus and merus. Its dactylus, together with that of the fourth leg, is the shortest of all. The propodus of P.5 bears a small anteroventral tooth, which is less than one third as long as the dactylus.

The anterior margin of the thoracic sternum is convex or slightly sinuous without a trace of a median incision. The first sternite bears a median row of three rather indistinct tubercles. The entire surface of the sternum is regularly granulated and pitted, except in the grooves. Each sternite shows a low but distinct median tubercle in the posterior part. The posterior margin of the sternum shows no spines or teeth in either sex.

The second abdominal somite in our male specimens has distinct pleopods, with the endopod only slightly narrower and longer than the exopod. The second pleopods (on somite 3) resemble the first, are only smaller. The pleopods of somites 4 and 5 have the endopod reduced to a short finger-like lobe, while the exopod is similar to those of the previous pleopods, but smaller. The basal part of the uropods is smooth without tubercles, at most with a shallow groove.

Size

In the present male specimens cl. is 20 and 22 mm long, in the female cl. is 20 mm.

Colour

A coloured photograph of the type specimen shows an animal with a uniform dull pale reddish brown colour. The smooth anterior part of the second abdominal somite is pale bluish and the extreme anterior tips of the median carinae of abdominal somites II and III are white. The whole gives the impression that the animal may have been photographed some time after preservation. However, a colour photograph of a fresh specimen from Taiwan is likewise uniformly pale brown with the tubercles and ridges somewhat brighter than the rest; the sixth abdominal somite 9 is somewhat paler than the other somites and the tailfan is whitish in the basal part, transparent in the rest.

Bathyarctus formosanus ( Chan & Yu, 1992)

Figures

FIG. 4. — Bathyarctus chani n. gen., n. sp., New Caledonia, CHALCAL 2, stn CC 1, holotype (MNHN-Pa 1884), thoracic sternum. Scale bar: 2 mm.

FIG. 5. — Bathyarctus chani n. gen., n. sp., New Caledonia, CHALCAL 2, stn CC 1,

FIG. 66. — A, B, Bathyarctus rubens (Alcock & Anderson, 1894) n. comb.; A, Loyalty Islands, MUSORSTOM 6, stn DW 395, carapace length 14 mm (MNHN-Pa 1348), photo P. Laboute; B, Fiji Islands, BORDAU 1, stn CP 1446, (MNHN-Pa 1885), photo J. S. Philippe; C, Bathyarctus chani n. gen., n. sp., NW Taiwan, Su-Aou fishing port, photo T. Y. Chan; D, E, Scammarctus batei (Holthuis, 1946) n. comb.; D, Fiji Islands, MUSORSTOM 10, stn CP 1318, carapace length 16 mm (MNHN-Pa 1886), photo B. Richer de Forges; E, Fiji Islands, N of Vanua Levu, BORDAU 1, stn CP 1402, carapace length 16 mm (MNHN-Pa 1846), photo J.-S. Philippe.