(Figures 8–10)
Nematocarcinus tenuipes Spence-Bate, 1888: 812 (part, "Challenger" st. 232); Burukovsky, 1991: 42; 2000 a: 164; 2001 a: 1302; 2002 a: 11; 2002 b: 1515; 2003: 159; 2004: 558; 2005: 575; 2006 a: 769; 2007 a: 187; 2012: 187; 2013: 182.
Nematocarcinus productus — Spence-Bate, 1888: 811 (part, "Challenger", st. 237).
Nematocarcinus longirostris — Spence-Bate, 1888: 806 (part).
Nematocarcinus parvidentatus Spence-Bate, 1888: 814.
Nematocarcinus ensiferus — Rathbun, 1906: 926.
Nematocarcinus serratus Spence-Bate, 1888: 819; Zarenkov, 1968: 158.
Nematocarcinus serratirostris Burukovsky, 1991: 41.
Nematocarcinus ovalis Komai & Segonzac, 2005: 355.
Nematocarcinus ensifer — Cardoso & Serejo, 2007: 41.
Non Nematocarcinus tenuipes — Spence-Bate, 1888: 812, (part, "Challenger", st. 218) (= N. productus Spence-Bate, 1888).
Material examined. Oceanprof I: A–1, 22o 45´S / 40 o 10´W, 1322 m, 2 ovigerous females (22.58–24.11), MNRJ 19233; A–6, 22o 27´S / 39 o 52´W, 1649 m, 1 male (18.2), 1 female (20.6), 4 ovigerous females (21.8–27.8), MNRJ 19177; A–8, 22o 49´S / 40 o 16´W, 1305 m, 1 ovigerous female (23.2), MNRJ 19179; A–12, 22o 12´S / 39 o 47´W, 1640 m, 1 male (21.2), 1 ovigerous female (27.0), MNRJ 19176; A–15, 21o 50´S / 39 o 47´W, 1649m, 3 ovigerous females (22.7–25.6), MNRJ 19178.
Oceanprof II: A–1, 22o 41´S / 40 º07´W, 1318 m, 4 females (17.0– 21.7), MNRJ 19984; A–9, 22o 39´S / 40 o01´W, 1605 m, 1 ovigerous female (22.2), MNRJ 19997; A–17, 22o 15´S / 39 o 51´W, 1332m, 1 female (21.5), MNRJ 19998; A–18, 22o 15´S / 39 o 47´W, 1627m, 1 ovigerous female (24.7), MNRJ 19960;
Habitats. Hab 1, 23o 51 'S / 41 o02'W, 1931 m, 1 male (20.4), 1 female (21.3), 2 ovigerous females (19.7, 23.4), MNRJ 21750; Hab 3, 22o 54 'S / 40 o 17 'W, 1886 m, 4 males (16.1–21.6), 2 females (24.2, 25.6), 1 ovigerous female (23.0), MNRJ 21749; Hab 5, 22o 20 'S / 39 o 42 'W, 1900 m, 3 males (18.6–20.4), 3 females (19.5–23.9), 6 ovigerous females (20.2–24.6), MNRJ 21748; Hab 6, 21o 51 'S / 39 o 41 'W, 1912 m, 1 female (24.3), 3 ovigerous females (22.6–24.3), MNRJ 21745; Hab 7, 21o 36 'S / 39 o 35 'W, 1889 m, 4 males (20.1 –21.0), 3 females (21.4–22.9), 4 ovigerous females (21.5–23.6), MNRJ 21746; Hab 8, 21o 7 'S / 39 o 38 'W, 1890 m, 6 males (16.2–21.4), 2 females (21.9, 23.0), 7 ovigerous females (20.8–25.5), MNRJ 21747; Hab 13, 21o 40 'S / 39 o 57 'W, 989 m, 1 male (13.3), 1 female (13.4), MNRJ 21751.
REVIZEE: E–0520, 13 o 21 ’S / 38 o 16 ’W, 2137 m, 3 males (16.2–21.5), 1 female (21.8), MNRJ 14717; E–0525, 20 o08’S / 38 o 38 ’W, 1639 m, 1 male (carapace lost in part), MNRJ 14712; E–0527, 19 o 50 ’S / 39 o 10 ’W, 1402 m, 1 ovigerous female (24.6), MNRJ 23454; E–0551, 21 o07´S / 39 o 49´W, 1642 m, 1 female (21.6), 3 ovigerous females (21.6–27.1), MNRJ 14698; E–0552, 21 o07’S / 39 o 46 ’W, 1694 m, 1 female (22.7), MNRJ 14703.
MAR-ECO: Superstation 8, WR Local station 201, 30o00’S /02o 49 ’E, 1074 m, 2 males (8.2–22.9), 4 females (14.8–22.1), MNRJ 22585; Superstation 9, WR Local station 201, 32o 50´S /01o 49´E, 1107 m, 5 females (11.2–23.7), 2 ovigerous females (17.4 –29.0), MNRJ 22588; Superstation 4, SEMS Local station 201, 0 4 o 40`S/ 12 o 16`W, 2014 m, 1 ovigerous female (19.0), MNRJ 22589; Superstation 7, WR Local station 201, 29o 27´S / 0 1 o 08´E, 3721 m, 1 female (12.9), MNRJ 22590.
Additional material: NMNH: 35 o09`N / 139 o 19`E, North Pacific, Japan, 1122m, coll. Albatross, 4 females (13.3 –17.0), id. Burukovsky, USNM 183440; North Pacific, Japan, 1057 m, coll. USFC, 1 ovigerous female (21.0); 32 o 34`N / 132 o 21´E, id. Burukovsky, USNM 183537; 30 o 34`N / 129 o 19`E, North Pacific, Japan, 804m, coll. USFC, 5 females (12.3 –15.0), 1 ovigerous female (17.9), id. Burukovsky, USNM 183414.
Description. Body moderately slender; integument moderately hard, not membranous, surface smooth, shiny. Rostrum straight or slightly raised up; overreaching antennular peduncle with more than one third of its length (Fig. 8 A, C, E) or with less than one third of its length (Fig. 8 B, D); distance from rostrum apex to the rostrum distal dorsal tooth is similar than that between the remaining rostrum dorsal teeth (Figs. 8 A, B, E; 9 A, B) or wider than that (Fig. 8 C, D); rostrum dorsal margin (including postrostral crest) with 15–40 teeth (Figs. 8 A–E; 9 A, B), distance between teeth becoming wider distally; rostrum ventral margin unarmed (Fig. 8 B, E) or with one badly developed tooth (Fig. 8 C), or with one well developed tooth lying: between the apex and first dorsal tooth (Fig. 8 D), under the first dorsal tooth (Fig. 8 A), or after the first dorsal tooth (Fig. 9 A), in few cases two teeth can be present (Fig. 9 B).
Eyes normally developed, its width noticeably larger than the diameter of the eye stalk.
Posterodorsal margin of third abdominal somite somewhat developed, rounded. Continuation of its sides when crossing forms an obtuse angle of about 90 o or less (Fig. 9 C, D). Fifth abdominal somite pleura with its sides intersecting at an angle near 90 o, with distal tooth (Figs. 9 E, F; 10 A). Inner surface of the anterior margin of the pleura of the fifth abdominal somite with elongated, shallow but clearly noticeable ridge.
Distoventral organ at sixth abdominal somite formed by two single parallel rows of long plumose setae, relatively widely spaced, extending to posterior margin of spots (Fig. 10 B); spots located at the sideways surface of sixth abdominal somite; spots length 2–3 times its width, distance between them is 2–3 times its width (Fig. 10 B).
Telson with 8 pairs of dorsolateral spines; without accessory spine (Fig. 10 C, D).
Distribution. Nematocarcinus tenuipes presents a tropical-subtropical cosmopolitan distribution (Fig. 11).
At Southeastern Atlantic it occurs at Gabon, Angola and Namibia coasts; and also at South Mid Atlantic ridge, from 2470 to 2840 m depth (Burukovsky 2007 a; 2012); Nematocarcinus tenuipes is recorded herein for the first time to the Southwestern Atlantic, from off Bahia to Rio de Janeiro states, Brazil, from 989 to 1931 m depth.
At Indian and Pacific Oceans N. tenuipes occurs from the Agulhas Bank and Mozambique Strait up to Taiwan, Japan, New Caledonia, Hawaii, Vanuatu, Fiji and Tonga Islands at depths of 630–3075 m (usually 1400–1700 m) (Burukovsky 1991; 2000 a; 2002 c; 2012; 2013). In the Eastern Pacific this species is recorded at the East Pacific rise (12 ° 45 'N / 103 ° 55 'W, 2558–2619 m), and Chile continental slope (33 ° 42 'S / 78 ° 18 'W, 2520 m; 42 ° 43 'S / 82 ° 11 'W, 2570m) (Burukovsky 2000 a; 2001 a; 2002 a; 2002 b; 2003; 2006 a; 2012; 2013).
Remarks. Comparing the southwestern Atlantic material with Burukovsky (2000 a; 2012; 2013) data, we observed that many features fit very well as rostrum dorsal teeth, third abdominal somite dorsal margin, fifth abdominal somite pleura, distoventral organ with a single pair of parallel rows of setae beginning at spots distal margin; some features present small differences as rostrum length, distoventral organ spots length and distance between spots; and only one feature show a high difference, the rostrum ventral teeth; we consider that all the observed variations are occurring at populations level (intra-specific variations) and they were included at species description.
Considering Nematocarcinus species with a relatively long rostrum, far overreaching the third antennular peduncle segment, there are five species with similar structure of the distoventral organ at sixth abdominal segment: N. exilis Spence-Bate, 1888; N. faxoni Burukovsky, 2001; N. poupini Burukovsky, 2007; N. productus Spence-Bate, 1888 and N. tenuipes Spence-Bate, 1888. In this five species the distoventral organ is formed by two rows of setae extending to posterior margin of spots, curving around spots medially, slightly diverging at anterior margin of spots, then extending almost parallel to each other. In N. poupini the spots length is 2.5 times greater than its width and the distance between them is similar to its width (Burukovsky 2000 a; 20091 b; 2002 b; 2007 b; 2012). In the remaining four species the spots length is about 2 times its width and the distance between them is approximately 2 to 2.5 times greater than its width. Due this high similarity of the distoventral organ structure other diagnostic features should be used to distinguish these species, as follows:
1) Rostrum size and ventral teeth
The rostrum shape is similar in these five species but in N. exilis the rostrum is shorter, never reaching scaphocerite tip. Besides that, in N. exilis the rostrum ventral margin is unarmed, while in N. tenuipes and in N. productus it can present a spine (but sometimes it is also unarmed). In N. faxoni the rostrum ventral margin usually present 2–3 teeth (rarely it present five teeth or is unarmed).
2) Posterodorsal margin of third abdominal somite
In N. productus there is a strongly developed projection with concave margins that partially overlap fourth abdominal somite, the continuation of its sides are crossing at an acute angle, but the projection tip is rounded. This projection is moderately developed in N. tenuipes, N. faxoni and N. poupini, its margins are slightly convex, the continuation of its sides are crossing at an angle slightly more than 90 °, the projection tip is broadly rounded. The projection in N. exilis is badly developed, continuation of its sides crossing at an angle of more than 120 °.
3) Fifth abdominal somite pleura and inner surface of its anterior margin
In N. productus the pleura sides are intersecting at an angle slightly less than 90 o, while in N. tenuipes this angle is slightly more than 90 °, in N. exilis and N. faxoni it is always somewhat more than 90 ° and in N. poupini is near to 90 °.
N. productus present a high oval tubercle at inner surface of anterior margin of fifth abdominal somite pleura, while in N. tenuipes, N. faxoni and N. poupini the tubercle is low and in N. exilis there is a low elevation, but not so well defined as a tubercle.
4) Species size
Nematocarcinus exilis is the smallest species in this group. Females of N. exilis mature early and the maximum carapace length does not exceed 23 mm (Burukovsky 2002 b) whereas in the other four species the minimum carapace length of ovigerous females is 19–20 mm and the maximum reaches 26–30 mm.
It can be stated that all five species are very close to one another but differ in sufficient features to consider them as separate species.
Besides that, some distributional aspects should also be considered when distinguishing these species. Nematocarcinus tenuipes is the only species of the genus with a tropical-subtropical cosmopolitan distribution, known at depths from 630 to 3075 m (usually from 1400 to 1700 m) (Burukovsky 2000 a; 2012; 2013).
Nematocarcinus exilis occurs in the Eastern Atlantic from 62 ° 17 'N to Morocco and Canary Islands (900–2300 m), including the Mediterranean Sea, at depths from 1033–4765 m (Cartes & Sarda 1993; Türkay 1998; Burukovsky 2002 b; 2012).
The distribution area of N. faxoni includes of two regions: East and West Pacific Ocean. The first region is limited by the coordinates 26 ˚ 58 '– 16 ˚ 33 'N/ 99 ˚ 52 '– 1 ˚ 28 'W and the second region is limited by 27 ˚ 58 '– 23 ˚ 47 'N/ 67 ˚– 78 ˚W and 30 ˚00'– 32 ˚ 50 'S/01˚ 49 '–02˚ 49 'E. In both regions this species occur at depths from 898 to 1839 m (usually, in the first region from 1100 to 1200 m and in the second region from 1047 to 1300 m) (Burukovsky 2001 b; 2012).
Nematocarcinus productus is found in the Indo-West Pacific from Mozambique Channel to Japan, Admiralty Islands and New Caledonia, but more often at Western region of the Indo-West Pacific, at depths from 1500 to 4260m (usually at depths of about 2000 m) (Burukovsky 2000 a; 2012; 2013).
Finally, Nematocarcinus poupini is so far known only from the Southwestern Pacific Ocean, from Austral Island to the east of Rapa Nui Island (27 °37,9'– 27 °38,2'S / 144 °15,2'– 144 °15,4'W) at depths from 840 to 1300 m (Burukovsky 2007 b; 2012).
Despite the relatively limited material about the distribution of these five species we can conclude that these are vicariate species, sharing the bathyal areas of tropical and subtropical waters (Burukovsky 2013).