Holthuisana tikus, Wowor & P. K. L. Ng, 2009

Wowor, Daisy & Ng, Peter K. L., 2009, Two new species of Holthuisana Bott, 1969 (Crustacea: Decapoda: Brachyura: Gecarcinucidae) from West Papua, Indonesia, Zootaxa 2071 (1), pp. 50-60 : 54-59

Holthuisana tikus n. sp.

( Figs. 3 , 4C , 5E–H )

Material examined. Holotype: male (31.6 mm x 25.5 mm) ( MZB Cru 2184), Kampung Lopintol, Waigeo, Teluk Manyailibit District , Raja Ampat Regency, Papua Barat Province, coll. N. Supriyatna, 10 Jun 2007.

Paratypes: 1 female (36.3 mm x 27.8 mm) ( MZB Cru 2185), same data as holotype . 1 female (22.6 mm x 17.9 mm) ( ZRC), Kampung Lopintol, Waigeo, Teluk Manyailibit District , Raja Ampat Regency, Papua Barat Province, coll. E. Cholik, 2 Jun 2007 .

Type locality. Waigeo, West Papua Province, Indonesia.

Comparative Material. Paratelphusa (Liotelphusa) ingrami subconvexa Roux, 1927: 1 syntype male (32.1 mm x 26.1 mm) ( MZB Cru 017), Pionierbivak, Mamberamo basin, New Guinea [= Papua Province, Indonesia], coll. W. C. van Heuren, 4 Aug 1920; 1 syntype male (26.3 x 21.3 mm) ( MZB Cru 041), Doormanpad Bivak, Point 1410 m, Mamberamo basin, New Guinea [= Papua Province, Indonesia], coll. W. C. van Heuren , 1920.

Description (holotype). Carapace length 0.8 times carapace width, high; carapace height slightly more than half carapace width, distinctly convex longitudinally; anterior part curved downwards, slightly convex transversely; greatest width slightly after anterior third of carapace; region slightly swollen at epigastric ridge level, smooth with scattered pits; epigastric lobes weakly convex, separated by short deep groove; cervical groove distinct but obsolescent before reaching anterolateral margin; H-shaped central groove distinct. Frontal margin emarginated medially, positioned level with external orbital angles; one-fifth carapace width, about one-third fronto-orbital width. Frontal median triangle distinct, merge with true frontal margin; about eight times as wide as high, upper margin as wide as frontal margin. External orbital angle short; anterolateral margin strongly convex, almost smooth, with crista which becomes undiscernible near posterolateral margin; epibranchial (first anterolateral) tooth small, broadly rounded, separated from rest of margin by small incision. Posterolateral margin relatively short, sinuous, with weak oblique striae. Posterior carapace margin almost straight, less than half maximum carapace width. Orbit ovate, positioned obliquely, inner margin higher than outer margin; slightly larger than eyes. Eyes well developed; cornea ovate, fully pigmented. Antennules folding transversely. Basal antennal segment lodge inside orbit. Mandibular palp deeply bifurcated. Third maxillipeds fill entire buccal cavity when closed; merus, three-fourths as long as wide, about half as long as ischium, anteroexternal angle rounded; exopod narrower than ischium, with well developed flagellum.

Chelipeds unequal; right larger. Major chela with palm relatively swollen, smooth; fingers longer than palm, surfaces finely granular with scattered pits along indistinct longitudinal grooves, tips corneous, crossing when fingers closed; fingers slightly gaping proximally, cutting edges of fingers with alternating small, large teeth; carpus short, conical with large tooth on inner margin, small tooth posterior to it, outer surface with many short finely granular rows; merus with upper margin serrated, upper outer surface with several finely granular rows. Minor chela relatively slender, fingers closing almost entire length; dentition similar to major chela; other segments similar but relatively more slender.

Ambulatory legs relatively slender, second leg longest, fourth leg shortest. Dactylus slender with 4 longitudinal spine ridges. Propodus as long as or slightly shorter than dactylus, rugose; lower margin with longitudinal row of 3–5 spines; upper margin with simple longitudinal ridge, longitudinal row of 3–5 spines on first, third, fourth ambulatory legs. Carpus as long as or slightly shorter than propodus, first to third ambulatory legs with longitudinal ridge on upper surface. Merus rugose, about twice as long as carpus, about 3.5 times as long as wide, upper margin rugose without subdistal tooth.

Thoracic sternum smooth with scattered pits. Male abdomen T-shaped; first somite very short, wide, with median transverse ridge; second somite about twice as long as first somite, about as wide as first, reaching coxae of fourth ambulatory legs; third somite slightly wider, longer than second somite, slightly narrowing anteriorly, lateral margin convex; fourth somite about as long as third somite, narrows anteriorly, trapezoid in shape; fifth somite somewhat longer than fourth somite, lateral margin slightly concave; sixth somite longest, about 1.5 times as long as fifth somite, lateral margin slightly concave; telson slightly longer than sixth somite, lateral margin concave with broadly rounded top.

G1 relatively robust, distal segment not separated from subdistal segment; distal part tubiform, gently curved outwards with relatively slender, bluntly truncated tip. G2 distinctly longer than G1, slender, straight, tip rounded; distal segment about 0.7 times length of proximal segment, more slender than previous segment.

Habitat. This species was collected on the forest floor under bushes near a village.

Etymology. The species name is derived from the way they were caught, in a mouse trap. Tikus is the Indonesian word for mouse. The name is used as a noun.

Colour. The carapace is brown with yellowish brown posterior portion; the chelae are reddish brown.

Remarks. Holthuisana tikus n. sp. most closely resembles H. subconvexa ( Roux, 1927) , but can easily be distinguished by the presence of weakly convex epigastric lobes (distinctly convex in H. subconvexa ); the frontal margin being at the level of the external orbital angles with the median part gently concave (frontal margin positioned behind level of external orbital angles and the median part deeply emarginated in H. subconvexa ); the branchial region is relatively flat (convex in H. subconvexa ), the teeth on the entire length of the cutting edges of the fingers of the major chela are similar, not differing markedly in size (a large median tooth on the dactylus and the pollex with several proximal tubercles in H. subconvexa ); the ambulatory merus has no subdistal tooth (with subdistal tooth in H. subconvexa ), the fourth ambulatory leg is relatively short with the distal end of the merus not reaching the widest part of the carapace when bent anteriorly (relatively longer leg which distal merus easily reaches widest part of carapace when bent anteriorly in H. subconvexa ); the fourth ambulatory merus is relatively stouter (length to width ratio 3.5 vs. 3.9); the male telson is slightly longer than the sixth abdominal segment (subequal in length in H. subconvexa ); the T-shaped male abdomen is relatively broader, with the posterior and the anterior margins of the sixth abdominal somite subequal in width (the posterior margin is not as wide as the anterior margin in H. subconvexa ); and most significantly, the G1 is relatively stouter (more slender in H. subconvexa ) (see also Bott 1974: Pl. 4, figs. 50–53). In any case, H. subconvexa is only known from the main island of New Guinea in Papua Province, Indonesia, some 600 km to the southeast of the type locality of H. tikus n. sp.

With regards to H. subconvexa , there are contradictions in Bott's description of this species. In 1970, Bott states that the G2 possesses a reduced flagellum, but in his 1974 study, the flagellum was described as long. Whether this is an error, due to damage or represents a real difference is not known. The G2 flagellum is well developed in the present type specimens (see comparative material above).

Distribution. So far only known from the type locality.

Figures

FIGURE 3. Holthuisana tikus n. sp., holotype male (31.6 mm x 25.5 mm) (MZB Cru 2184). A, overall view; B, thoracic sternum; C, frontal view.

FIGURE 4. A, B, Holthuisana lipkei n. sp., holotype male (35.5 mm x 27.7 mm) (MZB Cru 2186); C, Holthuisana tikus n. sp., holotype male (31.6 mm x 25.5 mm) (MZB Cru 2184). A, ventral view of carapace showing thoracic sternum and abdomen; B, C, outer views of large chelae.

FIGURE 5. A–D, Holthuisana lipkei n. sp., holotype male (35.5 mm x 27.7 mm) (MZB Cru 2186); E–H, Holthuisana tikus n. sp., holotype male (31.6 mm x 25.5 mm) (MZB Cru 2184). A, E, G1, ventral view; B, F, G1, dorsal view; C, G, tip of G1, ventral view; D, H, G2, ventral view. Scale bars: A–H = 1.0 mm.