Nematocarcinus evansi: Burukovsky (2000e), p. 1291, fig. 2; Burukovsky (2003), p. 85–87, fig. 23; Burukovsky (2012), p. 107–108, fig. 34.

Body robust, integument hard, surface smooth, shiny. Rostrum straight, slightly over-reaching distal end of antennular peduncle, reaching mid-length of scaphocerite; 0.34 times as long as carapace (Fig. 1A and Fig. 2A); dorsal margin armed with seven articulated teeth (an additional small tooth under proximal fifth tooth), including four on rostrum proper and three on carapace posterior to orbital margin; space between teeth increasing distally, distance from apex to distal tooth longest, about one-third of its length; ventral margin armed with one small subdistal tooth (Fig. 1A). Antennal and pterygostomian teeth well developed.

Figure 1.  

Nematocarcinus evansi Burukovsky, 2000, MBM189203, female (A–F) N. undulatipes Spence Bate, 1888, MBM189205, female (G–H). A anterior part of carapace and cephalic appendages, lateral view; B pleomere 3–4, dorsal view; C left pleura of fifth pleomere, lateral view; D right pleura of fifth pleomere, lateral view; E sixth abdominal somite, ventral view; F telson, dorsal view; G rostrum, lateral view; H distoventral organ, ventral view. Scales: 1.0 mm.

Figure 2.  

Photographs: A Nematocarcinus evansi Burukovsky, 2000, MBM189203, female; B Nematocarcinus undulatipes Spence Bate, 1888, MBM189205, female; C Nematocarcinus exilis (Spence Bate, 1888), SRSIO20080316, female; D Nematocarcinus exilis (Spence Bate, 1888), SRSIO20080316, male.

Eyes normally developed; cornea wider than eye stalk.

Third maxilliped not reaching distal end of scaphocerite; ultimate segment 0.71 times as long as penultimate segment, not markedly broadened at middle, armed with four apical spinules; antepenultimate segment shorter than distal two segments combined, armed with 4–6 spines on lateral margin and two distal spines; exopod slightly shorter than antepenultimate segment.

First pereiopod slender, over-reaching the end of scaphocerite by distal half-length of carpus. Ischium of first pereiopod with four ventrolateral spines, merus unarmed; ischium of third pereiopod with one distolateral spine. Other pereiopods lost.

Posterodorsal margin of third pleomere rounded, continuation of its sides forming an angle of about 120° (Fig. 1B). Pleura of fifth pleomere without bump on inner sides, terminating by a sharp tooth curved downwards in left side (Fig. 1C), a small spine present under distal tooth on the right side (Fig. 1D).

Ventral organ at sixth pleomere formed by two single rows of long plumose setae and two spots; setae rows cambered in front half and nearly parallel in distal half, extending to front of spots; spots 1.96–2.01 times as long as wide, distance between spots about 1.04 times spots width (Fig. 1E).

Telson armed with nine pairs of dorsolateral spines, two pairs of distal spines and a pair of accessory spines in middle of telson (Fig. 1F).

Colour, bright red (Fig. 2A).

Previously only known from the waters of south-western Australia (20°16'03''S, 113°13'05''E), the Indian Ocean, at depths from 913–916 m (Burukovsky 2000e, Burukovsky 2012). Presently recorded from the South China Sea, the Pacific Ocean.

The present material is consistent with the original description of N. evansi (Burukovsky 2000e, Burukovsky 2012), especially the features of the rostrum and distoventral organ. Small differences were also observed: the South China Sea sample has a sub-spine under the proximal fifth tooth of the rostrum and distal tooth of the right pleura of the fifth pleomere. However, these should be considered individual variations. A slender specimen (MBM189205, female, CL 17.5 mm) was collected at the same sampling station, but its rostrum was broken (Fig. 1G–H Fig. 2B). It closely resembles N. evansi apart from its distoventral organ, which is most like that of N. undulatipes Spence Bate, 1888. According to Burukovsky (2012), the only difference between N. evansi and N. undulatipes is that the latter has the distance between spots of a half-spot width and the unparallel setae rows (distal part) of the distoventral organ in the sixth pleomere. The slender specimen was consistent with this and, thus, was identified as N. undulatipes, which was previously recorded in the South China Sea (Liu 2008). Furthermore, the COI genetic distance between these two specimens is 13.6%, only slightly less than the average genetic divergence of genus Nematocarcinus (16.0%, n = 20). Partial sequences of the COI and 16S rRNA genes of these two samples were deposited in GenBank for future research (OP093562, OP093563, OP089179, OP089180).

Stochasmus exilis: Spence-Bate (1888), p. 822–824, pl. 82, fig. 14.

Nematocarcinus exilis: Crosnier and Forest (1973), p. 116–123, fig. 32d, e; 33d, e, f; Abello and Valladares (1988), p. 100, fig. 4; Turkay (1998), p. 1787–1794, fig. 2; Burukovsky (2012), p. 108–112, fig. 35.

Body moderately slender, integument moderately soft, surface smooth. Rostrum nearly straight, slightly upturned at tip and concave in middle. Rostrum of female specimen over-reaching distal end of antennular peduncle by one-third of its length, reaching to distal one-third of scaphocerite, about half-length of carapace (Fig. 3A and Fig. 2C); dorsal margin armed with 32 subequal teeth, including 23 on rostrum proper and nine on carapace posterior to orbital margin, distal four teeth basally sub-articulated, others all articulated; apex somewhat trifurcated (Fig. 3B); ventral margin unarmed. Rostrum of male specimen slightly over-reaching distal end of antennular peduncle, only reaching to mid-length of scaphocerite, about 0.37 times as long as carapace (Fig. 2D); dorsal margin armed with 25 subequal teeth, including 18 on rostrum proper and seven on carapace posterior to orbital margin, distal four teeth basally sub-articulated, others all articulated; apex bifid (Fig. 3C). Antennal and pterygostomian teeth well developed.

Figure 3.  

Nematocarcinus exilis (Spence-Bate, 1888), SRSIO20080316. A female, anterior part of carapace and cephalic appendages, lateral view; B female, distal part of rostrum, lateral view; C male, distal part of rostrum, lateral view; D female, pleomere 3–4, dorsal view; E female, left pleura of fifth pleomere, lateral view; F same, inner view; G female, sixth abdominal somite, ventral view; H female, telson, dorsal view. Scales: 1.0 mm.

Eyes normally developed; cornea wider than eye stalk.

Third maxilliped reaching to distal quarter of scaphocerite; ultimate segment 0.76 times as long as penultimate segment, not markedly broadened at middle, armed with slender apical spinule; antepenultimate segment subequal in length to distal two segments combined, armed with 8–9 spines on lateral margin and two distal spines; exopod reaching to distal two-fifths of antepenultimate segment.

First pereiopod slender, overreaching end of scaphocerite by distal one-sixth of carpus; ischium with four ventrolateral spines, merus with 1–2 ventrolateral spines; ischium of second pereiopod with one distolateral spine, merus with 6–9 ventrolateral spines; ischium of third pereiopod with one distolateral spine, merus with 6–7 ventrolateral spines; ischium of fourth pereiopod with 0–1 distolateral spine, merus with 5–6 ventrolateral spines; ischium of fifth pereiopod unarmed, merus with 1–5 ventrolateral spines.

Posterodorsal margin of third pleomere rounded, continuation of its sides forming an angle slightly larger than 120° (Fig. 3D). Pleura of fifth pleomere with distinct bump on inner sides, terminating by a prominent tooth (Fig. 3E–F).

Ventral organ at sixth pleomere formed by two single rows of long plumose setae and two spots; setae rows nearly parallel, extending to end of spots; spots 2.47–2.61 times as long as wide, distance between spots about 2.05 times spots width (Fig. 3G).

Telson armed with seven pairs of dorsolateral spines, two pairs of distal spines, without accessory spine (Fig. 3H).

Colour, crimson red in female, faint red in male (Fig. 2C–D).

Previously known in the eastern Atlantic from 62°17'N to Morocco and Canary Is-lands (900–2300 m) and the Mediterranean Sea at depths between 1033–4765 m. (Crosnier and Forest 1973, Burukovsky 2002b, Komai and Collins 2009, Burukovsky 2012). Presently recorded from the Kyushu-Palau Ridge, north-western Pacific.

At present, approximately 74.5% of Nematocarcinus species occur in the Indo-west Pacific origin, but only three species, N. ensifer (SI Smith, 1882), N. faxoni Burukovsky, 2001 and N. tenuipes (also occurring in the Indian Ocean), are distributed both in the Atlantic and Pacific Oceans (Burukovsky 2012). Under these conditions, we were hesitant to identify the present specimens as N. exilis at first. However, the features of the present specimens, such as a relatively long rostrum extending beyond the distal end of the antennular peduncle, but falling short of the distal margin of the scaphocerite, continuation of the posterodorsal margin of the third pleomere forming an obtuse angle, pleura of the fifth pleomere with a distinct protuberance on inner sides and arrangement of the spots and setae rows of the distoventral organ, coincide with the re-descriptions of N. exilis by Burukovsky (2002b) and Burukovsky (2012). Komai and Collins (2009) reported a closely related species, N. sp. aff. exilis from the Manus Basin of the south-western Pacific, based on a subadult female. By comparison between the present specimens and the Manus specimen, a number of differences could be found, such as the characters of the rostrum (over-reaching distal end of antennular peduncle by one-third of its length in female, all dorsal teeth articulated or sub-articulated, rostrum apex trifurcated or bifid versus only reaching distal end of antennular peduncle in female, only posteriormost three dorsal teeth articulated, rostrum apex simple), the antepenultimate segment of the third maxilliped (8–9 lateral spines versus 12), the pleuron of the fifih pleomere (armed with prominent posteroventral tooth versus tiny posteroventral tooth), the telson (armed with seven pairs of dorsolateral spines versus five) and the most important, the distoventral organs of the sixth pleomere (setae rows extending to the distal end of spots versus only reaching the anterior ends of the spots), based on which Burukovsky (2012) considered the Manus specimen to be a novel species that differed from N. exilis. In view of the differences discussed above, we agree with the inference of Burukovsky (2012) that the Manus specimen may represent a species unknown to science. However, just as Komai and Collins (2009) pointed out that the Manus specimen was a subadult female, more materials are need to clarify its taxonomic status. Partial sequences of COI and 16S rRNA genes of the present specimens were deposited in GenBank for further confirmation (OP093560, OP093561, OP089177, OP089178).

Nematocarcinus machaerophorus: Burukovsky (2003), p. 116–118, fig. 33; Burukovsky (2004), p. 1183–1184; Burukovsky (2006b), p. 1065, fig. 3a–d; Burukovsky (2012), p. 134–136, fig. 47.

Body moderately slender, integument hard, surface smooth. Rostrum damaged, remaining part nearly horizontal, dorsal margin armed with nine articulated teeth, including four on rostrum proper and five on carapace posterior to orbital margin, space between teeth increasing distally; ventral margin unarmed at remaining part (Fig. 4A). Antennal and pterygostomian teeth well developed (Fig. 4A).

Figure 4.  

Nematocarcinus machaerophorus Burukovsky, 2003, MBM189206, female. A anterior part of carapace and cephalic appendages, lateral view; B pleomere 3–4, dorsal view; C right pleura of fifth pleomere, lateral view; D sixth abdominal somite, ventral view. Scales: 1.0 mm.

Eyes normally developed; cornea wider than eye stalk.

Third maxilliped not reaching distal end of scaphocerite; ultimate segment 0.75 times as long as penultimate segment, not markedly broadened at middle, without apical spinule; antepenultimate segment subequal in length to distal two segments combined, armed with six spines on lateral margin and two distal spines; exopod falling short of distal margin of antepenultimate segment.

All pereiopods lost.

Posterodorsal margin of third pleomere rounded, continuation of its sides forming an angle slightly larger than 120° (Fig. 4B). Pleura of fifth pleomere without bump on inner sides, terminating by a sharp tooth (Fig. 4C).

Ventral organ at sixth pleomere formed by two single rows of long plumose setae and two spots; setae rows cambered laterally, extending to front of spots (Fig. 4D); spots located on a high tubercle-blister, about 1.98–2.01 times as long as wide, distance between spots slightly larger than a half of a spot width (Fig. 4D).

Telson damaged.

Previously only known from type locality, the Yeiao and Ua Pou Islands (Marquesas Islands Archipelago, central Pacific) at depths of 1000–1100 m (Burukovsky 2003, Burukovsky 2004, Burukovsky 2006b, Burukovsky 2012). Presently recorded from the South China Sea, north-western Pacific.

Species of Nematocarcinus are difficult to identify, not only because of their excessive morphological diversity, but also because of the fragility of the pereiopods and rostrum, which are usually damaged during collection. Burukovsky (2000f), Burukovsky (2000g) and Burukovsky (2012) proposed using the features of the tergum of the third pleomere, pleura of the fifth pleomere, distoventral organ of the sixth pleomere, the rostrum and the telson as key diagnostic characteristic markers. This greatly improved the taxonomy of Nematocarcinus. The present specimen had damaged rostrum and telson that could not be identified through morphology. Fortunately, DNA barcoding provides another efficient way to validate a species. BLAST results indicated a 98.57% match in the COI sequence between the present specimen (OP093564) and the holotype of N. machaerophorus Burukovsky, 2003 (KP759445, MNHN-IU-2011-5629), in which only seven nucleotide sites differed. The COI genetic distance between present specimen and the holotype of N. machaerophorus (KP759445, MNHN-IU-2011-5629) is 1.8%. The 16S rRNA sequence (OP089181) was identical to that of the holotype of N. machaerophorus (KP725571, MNHN-IU-2011-5629). Furthermore, the preserved characteristics of the present specimen, such as the tergum of the third pleomere, the pleura of the fifth pleomere and the distoventral organ, match those of N. machaerophorus, particularly the distoventral organ located on a high tubercle blister of the sixth pleomere. Its setae rows and spots exhibit a similar arrangement to that of the holotype (Burukovsky 2004, Burukovsky 2006b, Burukovsky 2012).