Notonyx sagittifer, Ng, Peter K. L. & Clark, Paul F., 2010

Ng, Peter K. L. & Clark, Paul F., 2010, Two new species of Notonyx A. Milne-Edwards, 1873 (Crustacea: Decapoda: Brachyura: Goneplacidae) from the Philippines and Fiji, Zootaxa 2509, pp. 30-38 : 31

Notonyx sagittifer n. sp.

( Figs. 1–3 )

Notonyx nitidus – Serène & Umali 1972: 82, pl. 8 figs. 9, 10, text-figs. 90-95 (not Notonyx nitidus A. Milne-Edwards, 1873 ).

Material examined. Holotype: 3 (8.74 × 6.42 mm) ( NMCR 1522), South Lagoon, Sitankai (= Sitangkai), Tawi-Tawi, Mindanao, Philippines, coll. F. G. Dayitt, Pele Expedition, 26 February 1964.

Diagnosis. Holotype: carapace ( Fig. 1 A) transversely subrectangular, 1.36 wider than long, frontal margin almost straight. Anterolateral margin short, entire, unarmed; posterolateral margin gently concave, slightly diverging towards posterior part. Dorsal surface of carapace smooth, without indication of regions except for shallow gastro-cardiac grooves; dorsal surface distinctly convex anteriorly, gently convex posteriorly. Eyes filling orbit ( Fig. 1 B); cornea pigmented, small. Small gape present between third maxillipeds when closed; merus quadrate, anterior margin almost straight, not concave, slightly shorter than ischium; anteroexternal angle of merus roughly level with tip of exopod ( Fig. 2 A). Chela with outer surfaces smooth, distinct keel on ventral margin extending almost to tip of finger ( Fig. 1 C); dorsal margin of propodus smooth, unarmed; inner margin of carpus rounded, with low tooth, inner margin denticulate. Walking legs absent on specimen. Thoracic sternum relatively broad; surface lightly pitted; sternites 1, 2 completely fused, separated from sternite 3 by distinct transverse suture; sternites 3, 4 fused except for lateral parts of sutures. Male abdomen ( Fig. 2 B) relatively broad, third somite broadest; telson triangular, lateral margins gently sinuous. G1 ( Fig. 3 A–D) relatively slender, gently curved outwards, subdistal part with hump-like structure, surface lined with numerous small spines, distal part not prominently elongated, distal folds not closing; outer lower margin rounded, entire. G2 ( Fig. 3 E–I) sinuous, longer than G1, distal segment sinuous, longer than basal segment; junction between distal, subdistal segments with concave surface surrounded by short serrae; distally spearshaped, tip appears slightly hooked, S-shaped.

Etymology. The species name is derived from the Latin sagittifer for carrying arrows; alluding to the crab possessing an arrow-headed G2.

Remarks. Although the present specimen is old and not well preserved, all the major diagnostic characters, with the exception of the walking legs, are present. The legs were not present even when it was reported by Serène & Umali (1972) and may have been lost during collection. The G1 structure, however, is so distinct, that we are confident it is different from all congeners.

Notonyx sagittifer n. sp. from the Philippines is closest to N. latus Ng & Clark, 2008 , from the Lesser Sunda Islands, Indonesia in the general form of the carapace and structure of the G1. Ng & Clark (2008: 23) had commented that N. latus appeared to differ from the Philippine specimen in carapace proportions, proportions of the ischium of the third maxilliped, relatively shorter male telson, and a differently shaped G1. The Philippine specimen can now be examined for all the characters noted above. While the relative carapace proportions are actually similar (carapace width to length ratio of N. sagittifer n. sp. is 1.36 while N. latus it is 1.40), there are several other differences. The third maxillipeds of the two species do differ in structure. In N. sagittifer n. sp., the anterior margin of the merus is less concave and the anteroexternal corner is roughly level with the tip of the exopod ( Fig. 2 A). In N. latus , the anterior margin of the merus is more prominently concave, and the anteroexternal corner is below the tip of the exopod (cf. Ng & Clark 2008: fig. 2B). There are no differences in the proportions of the ischium, the figure in Serène & Umali (1972: fig. 90) is somewhat inaccurate. The morphology of the carpus of the chelipeds of the two species do not differ markedly. The male abdomen figured by Serène & Umali (1972: fig. 91) shows a telson that is relatively short because the structure was drawn without compensating for the curve of the abdomen. The general form of the abdomen does not differ markedly from that of N. latus ( Fig. 2 B; Ng & Clark 2008: fig. 2E) although the lateral margins of somites 4–6 of N. sagittifer are gently convex rather than slightly concave. Most importantly, the G1 and G2 structures of the two species are significantly different. In N. latus , the G1 is almost straight along the median part, the distal part is elongated and beak-like, with the subdistal part not prominently swollen (cf. Ng & Clark 2008: fig. 3). In N. sagittifer n. sp., the G1 is gently curved, the distal part is not elongated, the distal folds do not close but form a U-shaped gutter-like structure, and the subdistal part is distinctly swollen and hump-like ( Fig. 3 A–D). The figure of the G 1 in Serène & Umali (1972: figs. 92, 93) is generally accurate except that the distal part is not bifid as depicted. The G2 of N. latus has the distal part curving on itself, forming a distinctive “S” (Ng & Clark 2008: fig. 4A). In N. sagittifer n. sp., the distal part is more spear-like ( Fig. 3 C, D). The figures of the G2 by Serène & Umali (1972: figs. 94, 95) are drawn with the entire structure tilted and gives the incorrect impression that the distal part was more hook-like in appearance. The differences observed above are not associated with size, considering the type of N. sagittifer n. sp. is somewhat smaller than that of N. latus . Rahayu & Ng (2010), who had a good series of specimens of a new species they described, showed that while the carapace, G1 and G2 does change slightly as specimens mature, none of them are significant. The differences observed here between N. latus and N. sagittifer n. sp., however, are of such a magnitude that they cannot be conspecific.

Figures

FIGURE 1. Notonyx sagittifer n. sp., holotype 3 (NMCR 1522), South Lagoon, Sitankai, Mindanao, Philippines. A, dorsal view of carapace; B, frontal view of carapace; C, outer view of left chela.

FIGURE 2. Notonyx sagittifer n. sp., holotype 3 (NMCR 1522), South Lagoon, Sitankai, Mindanao, Philippines. A, left third maxilliped; B, abdomen (telson and somites 2 - 6).

FIGURE 3. Notonyx sagittifer n. sp., holotype 3 (NMCR 1522), South Lagoon, Sitankai, Mindanao, Philippines. A, entire right G 1 (dorsal view); B, entire right G 1 (ventral view); C, distal part of right G 1 (dorsal view); D, distal part of right G 1 (ventral view); E, right G 2 (ventral view); F, right G 2 (dorsal view); G, tip of right G 2 (ventral view); H, tip of right G 2 (dorsal view); I, medial spinulation of right G 2 (ventral view).