Notonyx falcatus, Rahayu, Dwi Listyo, 2011

Rahayu, Dwi Listyo, 2011, A new species of Notonyx A. Milne-Edwards 1873 (Crustacea: Decapoda: Brachyura: Goneplacidae) from Maluku, Indonesia, Zootaxa 2982, pp. 33-39 : 33-38

publication ID	https://doi.org/ 10.5281/zenodo.207988
DOI	https://doi.org/10.5281/zenodo.6189830
persistent identifier	https://treatment.plazi.org/id/03E05C55-FFFB-AB52-90B4-15A9FC106975
treatment provided by	Plazi
scientific name	Notonyx falcatus
status

Treatment

Genus Notonyx A. Milne-Edwards, 1873 View in CoL

Notonyx falcatus n. sp. ( Fig. 1–4 View FIGURE 1 View FIGURE 2 View FIGURE 3 View FIGURE 4 )

Material examined. Holotype male, 15.2 × 11 mm ( MZB), Pulau Buntal, Seram Island, Maluku, Indonesia, 03°03'10''S 128°04'50''S, 29 June 1993. Paratypes, 2 females 16 × 11.2 mm, 8 × 5.8 mm ( ZRC), 1 juvenile female 5 × 4.2 mm ( MZB), same locality as holotype.

Diagnosis. Carapace subquadrilateral, wider than long (1.36 times as wide as long in holotype) ( Figs. 1 View FIGURE 1 A, 3A). Frontal margin slightly bilobed, about 0.33 times carapace width ( Figs. 1 View FIGURE 1 A, C, 3A). Anterolateral margin short, entire, curved, unarmed; posterolateral margin longer ( Figs. 1 View FIGURE 1 A, 3A). Dorsal surface of carapace smooth, without indication of regions except for shallow gastro-cardiac grooves; convex anteriorly, gently convex posteriorly ( Figs. 1 View FIGURE 1 A, 3A). Antennules relatively long, terminal setae reaching cornea ( Figs. 1 View FIGURE 1 B, 3A). Basal antennal joint small, short, positioned on orbital hiatus ( Fig. 1 View FIGURE 1 B, C). Eye peduncle moderately long, 0.54 times frontal width, cornea small ( Figs. 1 View FIGURE 1 A, C, 3A). Small gape present between third maxillipeds when closed ( Figs. 1 View FIGURE 1 B, 2A); merus shorter than ischium; antero-external angle of merus forms right-angle ( Fig. 3 View FIGURE 3 D). Chelipeds subequal, left larger ( Figs. 1 View FIGURE 1 C, 2B); fingers stout, dactylus smooth, shallow longitudinal groove on outer surface; fixed finger with shallow longitudinal groove medially, low longitudinal keel on ventral margin continues to palm, palm smooth; inner margin of carpus with acute tooth ( Fig. 3 View FIGURE 3 C), clump of short setae on inner margin; merus with long, stiff setae on anterior, posterior margins. Ambulatory legs relatively long ( Figs. 1 View FIGURE 1 A, B, 3E), smooth; dactylus with carina on lateral surface; sparse setae on upper, lower margin of propodi, carpi, meri.

Male thoracic sternum relatively broad; surface lightly pitted; sternites 1, 2 fused, separated from sternite 3 by distinct transverse suture; sternites 3, 4 fused with only lateral incision visible ( Figs. 1 View FIGURE 1 B, 2A). Male abdomen triangular, relatively narrow with 7 movable somites including telson; somite 1 underneath carapace, wider than somite 2; somite 2 longitudinally narrow; somite 3 widest; somites 4 to 6 tapering to rounded telson which is slightly longer than somite 6 ( Figs. 1 View FIGURE 1 B, 2A, 3B). G1 relatively stout, slightly bent inward on distal two-fifth ( Figs. 4 View FIGURE 4 A–C), continue to slightly curve, form hook-like projection, tapering at tip; distolateral part with row of spines, followed by longitudinal smooth area, flanked by row of spines on dorsal and ventral areas, mesial area with numerous short spines. G2 long ( Fig. 4 View FIGURE 4 D, E), much longer than G1, distal segment longer than basal segment, distal third of distal segment curved inward, tip sickle-shaped, directed anteriorly armed with spiniform setae.

Etymology. The name is derived from the Latin falcatus , meaning sickle-shaped, alluding to the sickle-shaped of the tip of the G2.

Remarks. The broad carapace, the relatively long pereopods and the hook-like distal tip the G1 of Notonyx falcatus n.sp. suggest this species is closest to N. latus Ng & Clark, 2008 , from Kei Islands, Lesser Sunda Islands, Indonesia and N. sagittifer Ng & Clark, 2010 , from the Philippines. Although the G1 of these three species posses a hook-like projection distally, this character is diagnostic. In N. falcatus n. sp. the G1 is distally bent and curved, tapering to a pointed tip with a row of spines and numerous prominent spines featuring on the distolateral, dorsal and ventral surfaces ( Fig. 4 View FIGURE 4 A–C). The G 1 in N. latus is almost straight for the entire length with the subdistal part being slightly dilated, bent, and end in an elongate truncated tip, the spines been situated on the distal part of the ventral and lateral areas (Ng & Clark 2008: fig. 3). In comparison, the G1 of N. sagittifer is gently curved outwards, with the distal part not being elongated, but folded forming a U-shaped gutter-like structure and being distinctly swollen subdistally (Ng & Clark 2010: fig. 3A–D). The difference in the shape of the G2 is more significant. In N. latus and N. sagittifer , the tip of the G2 appears S-shaped while that of N. sagittifer is distally spear-shaped (Ng & Clark 2010: fig. 3E–H). The G 2 in N. latus is tapered abruptly to distally form a sharp hook (Ng & Clark 2008: Fig. 4 View FIGURE 4 ). In N. falcatus n. sp., the G2 is strongly curved on the distal third, the tip is sickle-shaped and armed with numerous spiniform setae ( Fig. 4 View FIGURE 4 D, E).

Other diagnostic characters for N. falcatus n. sp. include the merus of the third maxilliped being shorter than the ischium ( Fig. 3 View FIGURE 3 D) instead of only slightly shorter in N. latus and N. sagittifer (Ng & Clark 2008: fig. 2B; Ng & Clark 2010: fig. 2A). The male abdomen of N. latus and N. sagittifer is also relatively broader (Ng & Clark 2008: fig. 2E; Ng & Clark 2010: fig. 2B) than that of N. falcatus n. sp. ( Fig. 3 View FIGURE 3 B). The male G2 of N. falcatus n. sp. is comparable to that of N. nitidus A. Milne-Edwards, 1873 in having the distal fifth curved. For N. nitidus the tip of the G2 is directed upward ( Clark & Ng 2006, fig. 3G), while in N. falcatus n. sp. it is sickle-shaped and directed anteriorly ( Fig. 4 View FIGURE 4 D, E). The male G1 of N. nitidus is only slightly bent ( Clark & Ng 2006, fig. 3H, I), instead of hook-shaped in N. falcatus n. sp. ( Fig. 4 View FIGURE 4 A–C). Finally, the carapace of N. nitidus is proportionately narrower ( Clark & Ng 2006: fig. 2A, 3A) than that of N. falcatus n.sp. ( Fig. 3 View FIGURE 3 A).

Distribution. The new species is only reported intertidally from the type locality, Pulau Buntal, Seram island, Maluku, Indonesia.

Discussion. So far six out of 11 Notonyx species are found in the Lesser Sunda Islands, Indonesia ( Clark & Ng, 2006; Ng & Clark, 2008; Naruse & Maenosono, 2009; Rahayu & Ng, 2010a, b). Notonyx castroi Rahayu & Ng, 2010 , N. falcatus n. sp., N. guinotae Rahayu & Ng, 2010 , N. latus are exclusively found in Indonesian waters. Two other species, N. gigacarcinicus Clark & Ng, 2006 , and N. kumi Naruse & Maenosono, 2009 are recorded from Phuket, Thailand and Japan respectively. Except for N. latus , the five species from Indonesia were collected on seagrass beds with coarse or fine sand and gravel substrates. The collections were made by digging (ca. about 10–20 cm) and sieving the substrate. The remaining five species have a reported limited distribution: N. nitidus from New Caledonia; N. angulatus Naruse & Takeda, 2010 , Japan; N. rayneri Ng & Clark, 2010 , Fiji; N. sagittifer , the Philippines and N. vitreus Alcock, 1900 was reported from Indian Ocean.