Bathyarctus steatopygus, Holthuis, 2002

Holthuis, Lipke B., 2002, The Indo-Pacific scyllarine lobsters (Crustacea, Decapoda, Scyllaridae), Zoosystema 24 (3), pp. 499-683 : 516-520

Bathyarctus steatopygus n. sp.

( Figs 6-8 )

TYPE MATERIAL. — Holotype: RV Manihine, cruise 320, dredge 3, ov. 11 mm ( RMNH D 49553); paratype: RV Manihine, cruise 331, stn 19, dredge 4, 1 11 mm ( RMNH D 49552). TYPE LOCALITY. — Kenya, Formosa Bay (Ungama Bay), 7°45’S, 40°28’E, 26 m.

ETYMOLOGY. — From the Greek stear (fat) and pyge (rump, buttocks). According to the Concise Oxford Dictionary, steatopygia is “the excessive development of fat on the buttocks, esp. of Hottentot women”. The name refers to the enormous dorsal swelling on the fourth and fifth abdominal somites in this species. The name is to be treated as an arbitrary combination of letters and therefore not subject to change with eventual change of gender in the accompanying generic name.

MATERIAL EXAMINED. — Western Indian Ocean, Kenya. Formosa Bay (Ungama Bay), RV Manihine, cruise 320, dredge 3, 7°45’S, 40°28’E, 26 m, 25.II.1971, A. J. Bruce don., 1 ov. holotype 11 mm ( RMNH D 49553). — Off northern Kenya, RV Manihine, cruise 331, stn 19, dredge 4, 2°20’S, 41°10’E, 176 m, stones and sponges, 9.X.1971, P. S. Sandher leg., A. J. Bruce don., 1 paratype 11 mm ( RMNH D 49552).

DISTRIBUTION. — The two only known specimens of the species were both taken off the coast of Kenya.

HABITAT. — The types were found at depths of 26 and 176 m. The bottom at one of the stations where this species was taken was described as with stones and sponges.

DESCRIPTION

The rostrum has a rounded tip and is only slightly constricted at the base. No rostral tooth is present, but there is a low inconspicuous median dorsal longitudinal ridge which extends posteriorly and carries a few tiny tubercles. The pregastric tooth is likewise absent, but the gastric tooth is distinct and triangular in lateral view; behind the gastric tooth there are five short longitudinal rows of tubercles. The cardiac tooth is welldeveloped about as large as the gastric tooth and provided dorsally with two longitudinal ridges each with five or six low tubercles; these ridges are separated by a straight median longitudinal groove. Scattered tubercles are present on the sides of the cardiac tooth. The branchial carina is widely interrupted by the cervical groove. In the gap is a tubercle. The anterior branchial carina ends in two teeth placed on the inner orbital margin; the posterior tooth is the larger of the two and placed higher than the anterior. A thin short carina connects the top of the posterior tooth with the orbital carina, which bears no tubercles. The anterior branchial carina itself is slightly uneven. A distinct postorbital tubercle is present. The posterior branchial carina ends in a distinct anterior tooth that overhangs the cervical groove; it is followed by a row of five distinct and a few inconspicuous tubercles. There are very few tubercles between the anterior postrostral and the anterior branchial carinae. The intermediate row between the posterior postrostral and posterior branchial carinae consists of five to seven rounded tubercles, the anterior two or three of which are placed on the posterior margin of the cervical groove. The lateral margin of the carapace has three anterolateral teeth (including the tip), one or two mediolateral and five or six large plus a few small posterolateral tubercles. The posterolateral carina ends anteriorly slightly above the posterior end of the mediolateral, the lateral margin forming an indistinct angle there. The intercervical carina shows tubercles; and the space between the posterolateral and posterior branchial carinae is filled by two more or less distinct rows of tubercles. The marginal groove along the posterior margin of the carapace is distinct, with a transverse row of distinct tubercles both before and behind it; the former are the larger. The posterior margin of the carapace shows a broadly rounded median incision.

The first abdominal somite shows a complete, but shallow transverse groove; there are about 10 short longitudinal ridges in the posterior half of the somite; the anterior half is smooth. Abdominal somites I to III have a distinct median incision in the posterior margin. The pleuron of the first somite has the lateral margin slightly concave in the middle; the antero- and posterolateral angles are broadly rounded. Above the middle of the lateral margin of the pleuron, and separated from it by a groove, is a large tubercle which is distinctly visible in lateral view. The second and third abdominal somites have their dorso-median carina smooth and somewhat V-shaped by the presence of a median groove in the posterior part. The carina of the third somite is somewhat higher than that of the second. The anterior half of somites II to V show irregular grooves forming a rather indistinct reticular pattern, which is most distinct in the posterior somites. Each of the tergites of somites II to V shows an oblique groove with tubercles before and behind it; but there is no arborescent pattern of narrow grooves. The pleura of the somites II to V end in a wide bluntly triangular or rounded top, which points down. The anterior margin of pleuron II shows a distinct rounded lobe in the basal part, no such lobe is seen in the other pleura. The posterior margin of pleura II and III have a small tooth in the distal part. The posterior margin of pleuron V shows a distinct lobe in the basal part. The surface of the pleura of somites II to V have a median groove flanked by a carina and many distinct tubercles. In pleuron II the groove is very distinct, in pleura III to V the carina is higher than in pleuron II. The fourth somite has the median dorsal carina broad at the base and extremely high, it is about twice as high as the carina of somite III; posteriorly it ends in a broad bluntly rounded top that reaches far beyond the base of the fifth somite; this top is bluntly rounded in lateral view, but in dorsal view it shows a distinct V-shaped median incision. The dorso-median carina of somite V is slightly lower than that of the fourth and has the top not rounded, but ending in a triangular point, which clearly reaches over the base of the sixth somite and is not incised at the top. The posterior margin of the sixth somite shows a posterolateral tooth at each angle, between these there are three large and a few smaller tubercles. The upper surface of this somite shows two wide grooves that converge anteriorly the rest of the surface carries several tubercles. The upper surface of the basal hard part of the telson has two rounded submedian tubercles near the anterior margin and a somewhat larger pair more posteriorly and farther apart. The posterior margin of this hard part has a broad triangular tooth at either lateral end and a smaller narrower tooth nearer to the median line.

The anterior margin of the antennular somite shows on each half a distinct broad triangular tooth; these two teeth are separated by a wide V-shaped median incision that is followed by a median groove.

The sixth segment of the antenna has the anterior margin rather straight and with six blunt teeth, the outer of these teeth is widest and has two incisions in the outer margin. The inner of the teeth is somewhat more pointed than the others. The inner margin of this segment shows a single appressed tooth. The anterior margin of the fifth antennal segment has a strong, dorsally carinate tooth at the inner angle and two much smaller teeth on the outer. The fourth segment is triangular and reaches beyond the sixth. The inner part shows a blunt, carinated distinct tooth. The anterior margin of this segment is serrate: it has a rather distinct rounded tooth in the inner third, and between this tooth and the apex of the segment there are seven to nine serrations, which become smaller distally. The outer margin of this fourth segment has three rather large teeth (not including the apex of the segment) and two to four smaller teeth in-between. The upper surface of the segment shows two distinct carinae: the normal oblique central carina ending in the apex of the segment, and a shorter in the outer half of the segment. The latter ends in the central of the lateral teeth and carries some small tubercles. A few scattered tubercles are present on the rest of the surface of the segment.

The anterior margin of the epistome is incised in the middle and has each half with a shallow median concave part.

The anterior margin of the thoracic sternum is narrow and slightly concave, there is no deep incision in the middle. Directly behind this margin is a distinct rounded carina with a rather irregular posterior margin. The carina merges with the carina along the lateral margin. The surface of the sternum is pitted and with short grooves. A median tubercle is found on somites II to V.

P.1 (in the females) is only slightly shorter and more robust than the others. The dactylus is somewhat shorter than the propodus, and about two thirds as long as the dactylus of P.2; it is practically as long as the dactyli of P.3 and P.4; the dactylus of P.5 is shorter. Apart from a few scattered hairs, no pubescence is seen on P.1 and P.2. The merus of P.1 to P.3 has two indistinct longitudinal grooves on the outer surface. The dactylus of P.3 has a fringe of short setae both on the dorsal and ventral margins, such a fringe is also present on the dorsal margin of the propodus, while some hairs are visible on the upper margin of the merus. P.4 has a continuous fringe of hairs on the dorsal margin of the dactylus, while both in P.4 and P.5 there are small pubescent patches in the upper distal part of propodus and carpus, as well as some hairs in the basal part of the upper margin of the merus. In the ovigerous female the dactylus of the fifth leg has a single dorsal fringe of hairs. The propodus has a rather wide tooth at the end of the lower margin; this tooth forms a subchela with the dactylus, of which, however, it does not reach the middle of its length.

Size

The two types, both being females (one ovigerous), have cl. 11 mm.

Figures

FIG. 6. — Bathyarctus steatopygus n. gen., n. sp., Kenya, Formosa Bay, holotype (RMNH D 49553); A, dorsal view; B, lateral view.

FIG. 7. — Bathyarctus steatopygus n. gen., n. sp., Kenya, Formosa Bay, holotype (RMNH D 49553), thoracic sternum.

FIG. 8. — Bathyarctus steatopygus n. gen., n. sp., Kenya, Formosa Bay, holotype (RMNH D 49553); A, anterior part of thoracic sternum; B-D, pereiopods 1 to 3; E, pereiopod 5; F, pereiopod 4. Scale bar: 2 mm.