Notonyx sagittifer Ng and Clark, 2010

Notonyx sagittifer Ng and Clark, 2010 View in CoL

( Figs. 10–12 View Fig View Fig View Fig )

Notonyx nitidus A. Milne-Edwards, 1873 : Serène &

Umali, 1972, p. 82, figs. 90–95, pl. 8 figs. 9–10. Notonyx sagittifer Ng & Clark, 2010, p. 31 , figs. 1–3. Notonyx aff. sagittifer : Takeda, 2023, p. 28, fig. 11C–E.

Material examined.ɹOse-zaki, Suruga Bay, 6 m depth, 1 Ə infested by a sacculinid parasite (cb 14.9 mm, cl 11.0 mm), NSMT-Cr 32425, 4-XI-2023, coll. H. Takakura; Ose-zaki, 2 m depth, sandy mud bottom, 1 8 (cb 15.0 mm, cl 10.5 mm), NSMT-Cr 32447, 28-IX-2024, coll. H. Takakura.

Remarks.ɹThe type species of the genus Notonyx , N. nitidus A. Milne-Edwards, 1873 , was explained in detail based on the holotype from New Caledonia and the topographical and other specimens by Clark and Ng (2006). It is remarkable that ten of twelve known species were described during six years from 2006 to 2011. The known species are well described and figured, but the definite identification is rather difficult due to the small size, less than cb 15 mm, and the smooth carapace of closely similar shape.

The present male infested by a sacculinid parasite has the short first and elongated other pleo- pods deformed with parasitism. The carapace, chelipeds and ambulatory legs are considered to show the original characteristics ( Figs. 10–12 View Fig View Fig View Fig ), and the female is of nearly same size as the male, with undifferentiated shape from the male. The two specimens examined are relatively large (cb 14.9 and 15.0 mm) and comparable with the larger five species in the genus, N. rayneri Ng and Clark, 2010 (cb 17.3 mm), N. falcatus Rahayu, 2011 (cb 16 mm), N. guinotae Rahayu and Ng, 2010 (cb 15.5 mm), and N. kumi Naruse and Maenosono, 2009 (cb 13.0 mm). In the present specimens, however, the carapace ( Figs. 10 View Fig , 12A View Fig ) is rather narrow, 1.36 wider than long in male and 1.43 in female. Although the carapace form may vary individually or with photographing, the carapace anterolateral margin of these specimens is so as to be sub-rectangular, being different from these large species. Among the known smaller species, the carapace proportion of the present male just agrees with that of N. sagittifer , the holotype of which is the old specimen from Mindanao, previously recorded by Serène and Umali (1972) as N. nitidus A. Milne-Edwards, 1873 ( Ng and Clark, 2010). The present male is apparently larger than the holotype of N. sagittifer (cb 8.74 mm), but it may be difficult to show the definite differences as regards the carapace shape and chela between the Philippine and Japanese specimens. In the present specimens examined, the frontal margin is almost straight, without median interruption ( Fig. 11B View Fig ); the posterior margin of the epistome is divided into three parts, with the median part weakly convex and medially incised ( Fig. 11B View Fig ); the male pleon is wide and triangular as a whole (fig. 11C); and both chelae are compressed and strongly crested along the whole lower margins of the palm and immovable finger ( Fig. 11A, C View Fig ). The male first gonopod is similar to the line drawings of that of the original description of N. sagittifer , but its tip is rather sharp and not so distinctly truncated as in the original figures, with more crowded tubercles at the subterminal part. The male second gonopod is so abnormally elongated like the female pleopod that its tip is not the form of arrow-head.

The female pleon is wide and covers the whole sternum, with the widest fourth pleonite and the telson slightly longer than the preceding pleonites. Each vulva is large, transversely ovate, with the anterior margin more strongly convex than the posterior margin, and located just on the suture between the fifth and sixth thoracic ster- nites, each occupying one-third as wide as each sternite.

Takeda (2023) recorded a small male (cb 5.0 mm) from the Palau Islands as Notonyx aff. sagittifer . In the specimen, unfortunately, the male pleon and first gonopod, and all the ambulatory legs are missing. The specimen was not positively identified to N. sagittifer , but may be not matured stage of that species, with fragile chelipeds.

Color in life.ɹWholly chestnut-color and partly paler, as reproduced in Fig. 10 View Fig .

Distribution.ɹDefinitely known only from Tawi-Tawi, Mindanao, Philippines, and probably from the Palau Islands. New to Japanese waters.