Figure 3 A–J; Plate 1 C–E
Material examined. Holotype, female (gravid) (NHMUK 2018.6), Southwest Indian Ocean, Coral Seamount, 41˚22.31'S, 42˚54.57'E, 732 m, ROV, stn 4.38, specimen JC066-3087, mooring site, on net containing whale bone, 20 November 2011.
Paratype. One female (gravid) (NHMUK 2018.7), Southwest Indian Ocean, Coral Seamount, ROV, stn 4.2, specimen JC066-4197, coral framework/rubble, 12 November 2011.
Description. Female holotype. Trunk (Fig. 3A, B) smooth, distinctly segmented, glabrous, neck short, width slightly less than trunk width; lateral processes longer than wide, separated by about own basal diameter. Ocular tubercle darkly pigmented, placed in line with anterior margins of ovigers, conical, two apical papillae; four eyes, large, equal size, lightly pigmented in the preserved specimen.
Proboscis widest at base, tapering slightly to a rounded tip.
Abdomen (Fig. 3J) unarticulated at base, inclined, length about four times maximum width, reaching to end of first coxae of fourth legs.
Chelifore scape reaching to tip of proboscis, arched in lateral view, chela fingers angled downwards in front of jaws (Plate 1E), slender, almost twice length of palm, gently bowed inwards, moveable finger slightly longer than immoveable finger, teeth sharp, uniform in size, immoveable finger with fourteen teeth, moveable finger with ten teeth, palm with many long setae on outer surface (Figs 3H, I).
Palp (Fig. 3G) five-segmented, segments 2 and 3 about equal length, segment 5 twice length of segment 4.
Oviger (Fig. 3E, F) ten-segmented, base touching first lateral processes, segment 4 longest, with prominent gland opening on posterior surface, terminal claw long, length about equal to segment 10, five teeth on inner margin, compound spine formula 7:5:5:5.
Third leg (Fig. 3C), second coxa 2.5 times length coxa 1, tibia 2 longest, tibia 1 longer than femur, tibia 2 with dense, fine setae, mostly shorter than diameter of trunk, femur and tibia 1 less setose, tarsus little more than half length of propodus (Fig. 3D), lined with about 20 spines on inner margin; propodal heel absent, sole lined with field of about 30 sharp spines and numerous shorter lateral spines, claw slightly more than one-third length of propodus, auxiliary claws flared outwards from bases, greater than half length of main claw. Gonopore large, distoventral surface of coxa 2 all legs.
Measurements of holotype (mm). Length trunk (frontal margin of cephalic segment to tip of 4 th lateral process), 2.160; length cephalon; 0.984; width across 2 nd lateral processes, 1.024; length proboscis (lateral), 0.744; greatest diameter proboscis, 0.336; length abdomen (lateral) 0.528. Palp: seg. 1, 0.120; seg. 2, 0.376; seg. 3, 0.352; seg. 4, 0.120; seg. 5, 0.240. Oviger: seg. 1, 0.088; seg. 2, 0.160; seg. 3, 0.160; seg. 4, 0.600; seg. 5, 0.520; seg. 6, 0.320; seg. 7, 0.224; seg. 8, 0.176; seg 9, 0.160; seg. 10, 0.160; claw 0.136. Third leg: coxa 1, 0.344; coxa 2, 0.848; coxa 3, 0.392; femur, 1.920; tibia 1, 2.400; tibia 2, 3.000; tarsus, 0.488; propodus, 0.880; claw, 0.304: auxiliary claws, 0.208.
Etymology. This species is named for Natalia Serpetti, who with Peter Lamont of the Scottish Association of Marine Science, Scottish Marine Institute provided most of the post-voyage material.
Remarks. The following species share a common habitus with the new species: N. arcuatum Child, 1995a, N. paucidens Gordon, 1932, N. sarsii, Meinert, 1899, N. signatum Mobius, 1902 and N. tenellum, (Sars, 1888). These species all possess auxiliary claws, lateral processes separated by about their own diameter, a moderately short cephalon neck, ovigers in contact with first lateral processes and in the general proportions of the tarsus and propodus (tarsus between half and one times propodus length). The new species can be distinguished by the following characters: from N. arcuatum by its much shorter chela palm and longer fingers; from the more setose N. paucidens by the much shorter lateral processes and abdomen; from N. sarsii by the absence of dorsally inflated trunk segments and shorter tarsus; from N. signatum by the much shorter chela palm and fingers with far fewer teeth and from the more setose N. tenellum by the much shorter propodal spines and shorter chela palm.
The tips of the chela fingers are a very dark colour. The unpigmented eyes contrast with the dark ocular tubercle.