Limnopilos sumatranus, Naruse, Tohru & Ng, Peter K. L., 2007

Naruse, Tohru & Ng, Peter K. L., 2007, On the taxonomy of the genus Hymenicoides Kemp, 1917 (Crustacea: Decapoda: Brachyura: Hymenosomatidae), with resurrection of Limnopilos Chuang & Ng, 1991, and descriptions of two new species, Zootaxa 1621, pp. 17-31 : 26-30

Limnopilos sumatranus new species

( Figs. 1 e, f, 7-9)

Material examined. Holotype: male, 4.7 × 5.5 mm, MZB Cru 1650, Jambi, Sg. Hitam, near junction into black water reserve, along Batang Hari, Sumatra, Indonesia (1°15´9.3" S, 104°6´49.6" E), coll. H. H. Tan et al., 5 Jun. 1996.

Paratypes: 1 male, 5.0 × 5.9 mm, ZRC 2007.0114; 21 males, 2.1 × 2.3 mm – 5.1 × 6.0 mm, ZRC 2007.0115; 7 females, 2.8 × 3.0 – 3.7 × 4.0 mm, ZRC 2007.0116; 28 ovig., 2.8 × 3.1 – 4.0 × 4.6 mm, ZRC 2007.0117; 3 males, 3.5 × 4.0 mm – 4.1 × 4.8 mm, 1 ovig., 3.8 × 4.3 mm, MNHN-B30394; 1 male, 4.6 × 5.1 mm, 1 female, 5.4 × 6.3 mm, MNHN-B30395; 3 males, 3.3 × 3.7 mm – 3.8 × 4.2 mm, 1 ovig., 3.5 × 4.0 mm, MZB Cru 1651. All paratypes were collected together with holotype.

Comparative material. Limnopilos naiyanetri ( Chuang & Ng, 1991) : 1 male, 5.9 × 6.0 mm, ZRC 1993.6520, holotype, Mae Nam Nakhon Chaisi, Amphoe Nakhon Chaisi, Changuat Nakhom Pathom, Thailand, coll. Naunsri, 1998; 19 males, 3.1 × 3.6 – 5.4 × 6.4 mm, 13 females, 2.9 × 3.1 – 4.5 × 5.0 mm, ZRC 1991.6521–6555, paratypes, same data as holotype. Limnopilos microrhynchus (Ng, 1995) : 1 male, 2.6 × 2.8 mm, QM W21466, Bengalon River, east Kalimantan, Indonesia (0°42´S, 117°38´E), coll. R. Powell & J. Powell, 16 Mar. 1996.

Description. Carapace ( Fig. 7 a) circular, CW 1.1–1.2 times CL (mean 1.13, n = 14); dorsal surface flat, surrounded by circular rim, regions well demarcated by grooves, H-shaped gastric groove continuous with cervical groove, cervical groove branching anteriorly, branches confluent with anterolateral rim. Rostrum vestigial, anterior median part of rim projecting slightly, tip with a few long setae. Lateral margin of carapace lacking tooth or lobe, side wall of posterolateral region slightly expanded laterally, with posterior longitudinal groove along posterolateral rim. Laterally flattened sharp tooth between antennules, completely disconnected from vestigial rostrum; orbit indiscernible, with a sharp conical tooth on outer part of eye, tooth visible from dorsal view. Epistome long, placed dorsally compared to buccal cavern, ischum of third maxilliped partially covering posterior margin.

Eyes moderately developed, visible dorsally. Antennule with long coxa, about twice length of basis. Third maxilliped ( Fig. 7 b) narrow, covering about one-quarter of buccal cavern; merus long, about one-half times of ichium, narrower than ischium; palp long, propodus slightly longer than half length of dactylus, dactylus longer than merus, tip of dactylus almost reaching proximal end of ischium; exopod short, reaching about proximal two-third of merus, with distinct flagellum.

Male with relatively wide abdominal cavity ( Fig. 1 e), sternal button present on just posterior to imaginary line joining inner ends of sutures between sternites 5 and 6. Female thoracic sternite 3 separated from sternite 4 by posteriorly convex rim, sternites 4–8 medially fused, vulva on imaginary line joining inner ends between sternite 6 on medial fused plate of thoracic sternum, vulva with longitudinally elliptical basal mount.

Cheliped symmetrical, more massive in males; cheliped of male with short merus, as long as carpus, ventral outer margin lined with long plumose setae, with subdistal tooth, ventral inner margin sparsely lined with low granules, inner surface of merus to carpus lined with long stiff setae, outer surface of carpus rounded, not strongly elevated, outer margin with small subdistal tooth; chela ( Fig. 7 c) with rounded palm, covered densely with long plumose setae from distal part of upper, lower margin of palm to both fingers; fingers with ovoid gape when closed; immovable finger with 3 teeth on proximal two-thirds, with subdistal tooth connected to tip of finger by thin lobe, forming hoof; movable finger similar to immovable finger, except for tooth on proximal part.

Ambulatory legs ( Fig. 7 a, d–g) slender, long; second, third legs subequal, longer than others, fourth shortest, inner margin of legs fringed densely with long plumose setae, outer margin lined with short curly setae; meri slightly longer than respective propodi, distal anterior angle ending in conical tooth; dactyli terminating in sharp tooth, first subdistal tooth of inner margin stronger than terminal tooth, 6–8 teeth (n = 7) of inner margin arranged throughout in fourth leg, 6–9 teeth only on distal half in second and third legs (n = 6), 2–4 teeth limited to distal third in first leg (n = 5), teeth of males larger than those of females.

Male abdomen-pleotelson ( Fig. 8 a) 6-segmented; first segment of male abdomen thick, hard, distal margin widely concave; second to fifth segments with distal margin concave medially, third segment widest; pleotelson trilobed, lateral lobes small, low; 2 small concavities on posterior margin, distal margin thickened, forming socket for sternal button ( Fig. 1 f) on inner surface. G1 ( Fig. 8 c) stout, strongly bent on distal twofifths, ventral outer surface longitudinally lined with long, stiff, distally plumose setae; distal inner end with 2 sharp processes, sub-inner process well separated from, larger than inner process, directed slightly lower than that of inner process, distal outer angle swollen, covered by tiny granule, outer ventral apex bat-like. G2 ( Fig. 8 d) short, base not strongly swollen. Female abdomen-pleotelson ( Fig. 8 b) demarcated to 6 segments, boundary between first and second segments movable, more or less fixed in other boundaries; second to fifth segments with corneous wide ridge medially, that of segment 6 only on proximal half, segment 6 longest, no suture separating pleotelson; pleopods ( Fig. 9 ) on second to fifth segments, long, biramous from near base, developing from distal outer angle of inner side of each segment.

Eggs spherical, small, diameter 0.32 – 0.34 mm [mean = 0.33, n = 10 from two females (2.8 × 3.1 and 4.0 × 4.6 mm)], attached on endopods of pleopods, exopods growing inwards, partially covering dome-shaped abdomen.

Habitat and distribution. The specimens were all collected from among the roots of a mass of floating vegetation near the centre of the stream, from which catfishes ( Leiocassis sp., Bagridae ) were also collected. The tannin-coloured acidic waters were gently flowing.

Etymology. The species is named after the type locality, Sumatra, Indonesia.

Remarks. Limnopilos sumatranus new species, is very close to L. microrhynchus Ng, 1995 , especially in having a vestigial rostrum. The main difference between the two species is the location of the sub-inner process of the distal end of the G1. It is more medially placed and directed more laterally in L. sumatranus than in L. microrhynchus , where it is closer to the inner process and directed more anteriorly ( Fig. 8 c). This difference is constant for the good series of specimens examined and evident even when similar sized specimens are compared ( L. sumatranus : 3 males, ZRC 2007.0115, 2.2 × 2.3–2.9 × 3.2 mm; L. microrhynchus : 1 male, QM W21466, 2.6 × 2.8 mm). In addition, small specimens of L. sumatranus have a distinct sharp subdistal tooth on the ventral outer margin of the cheliped merus (indiscernible in L. microrhynchus ) and an anterolateral margin which is less divergent posteriorly than in L. microrhynchus . Large individuals of L. sumatranus show a similar divergence of the anterolateral margin as in L. microrhynchus , but their difference is still obvious when similar sized specimens are compared.

Limnopilos microrhynchus was described from eastern Sabah (Ng, 1995), and the present specimens from eastern Kalimantan, extend its range further southwards, as well as into Indonesia for the first time.

Figures

FIGURE 1. Male abdominal cavity and pleotelson of Hymenicoides robertsi new species, and Limnopilos species. a, b, Hymenicoides robertsi new species (paratype, ZRC 2007.0109, 5.0 × 6.2 mm); c, d, L. naiyanetri Chuang & Ng, 1991 (ZRC 1991.6521 – 6555, 4.9 × 5.3 mm); e, f, L. sumatranus new species (paratype, ZRC 2007.0114, 5.0 × 5.9 mm). a, c, e, male abdominal cavity with sternal button (sb) and G 1; b, d, f, inner surface of male pleotelson.

FIGURE 7. Limnopilos sumatranus new species. a, habitus; b, third maxilliped, left; c, male right chela; d – f, male right first, third, and fourth ambulatory dactyli; g, female right fourth ambulatory dactylus. a, holotype male (MZB Cru 1650), 4.7 × 5.5 mm; b – f, paratype male (ZRC 2007.0114), 5.0 × 5.9 mm; g, paratype female (MNHN-B 30395), 5.4 × 6.3 mm. Scale bars, 1 mm.

FIGURE 8. Limnopilos sumatranus new species. a, male abdomen-pleotelson; b, female abdomen-pleotelson; c, left G 1; d, left G 2. a, paratype male (ZRC 2007.0114), 5.0 × 5.9 mm; b, paratype female (MNHN-B 30395), 5.4 × 6.3 mm; c, d, holotype male (MZB Cru 1650), 4.7 × 5.5 mm. Scales, 1 mm.

FIGURE 9. Limnopilos sumatranus new species. a, b, right second and third pleopods; c, d, left fourth and fifth pleopods; e, exopods. Paratype, ovigerous female (ZRC 2007.0117), 4.0 × 4.6 mm.