Nematocarcinus gracilipes Filhol 1884

Nematocarcinus gracilipes Filhol, 1884

(Figures 2–4)

Nematocarcinus gracilipes Filhol, 1884: 232; Crosnier & Forest, 1973: 123; García Raso, 1996: 734; Burukovsky, 2000c: 4; 2004: 558; 2009: 81; 2012: 116.

Nematocarcinus agassizii Faxon, 1893: 204; 1895: 158, pl. 42; Burukovsky, 2001b: 1432, fig. 3; 2004: 558 (key).

Material examined. MAR-ECO: Superstation 2, SEMS Local station 201, 0 0o 26´N/ 17o03´W, 902 m, 3 males (12.0–15.2), 39 females (12.6–27.6), MNRJ 22584; Superstation 2, SEMS Local station 201, 0 0o 26´N/ 17o03´W, 902m, 5 females (12.3–26.9), 1 male (13.4), MNRJ 22583.

REVIZEE: E–0507, 15o08’S / 38o40’W, 1026 m, 1 female (18.80), MNRJ 23447.

Additional material: MNHN: Atlantic Ocean, Cape Verde, “Talisman”, st. 120, 30.07.1883, 16 0 53΄N/25°12΄W, 618 m, 11 males (11.0–21.0), 19 females (11.0–22.0), 7 ovigerous females (18.0–22.0).

Collection Prince of Monaco 1896–1909. St. 114, 166, 663, 698, 1311, 1349, 2210, without coordinates and depths, 1 male (17.5), 5 females (14.0–23.5).

Ibero-Moroccan waters, “Cryos”, st. CP 09-108, 29.05- 10.06.1984, 36°48΄–34°21΄N, 09°28΄–07°24΄W, 859–1535 m, 1 juvenile (9.0), 36 males (11.5–2.5), 32 females (12.0–25.5), 10 ovigerous females (20.2–25.5).

Azores islands, “Jean Charcot”, st. 74, 180, 197, 240 (st. 197— 30.07.1883, 37°49.6΄N/ 27°01.3΄W, 815 m, other stations without dates, coordinates and depth), 1 juvenile (10.0); 10 males (11.5–25.5), 5 females (12.0–23.0).

NMNH: 0 4o 03`N/ 08o31`W, North Pacific Ocean, 899m, 6 males (22.1–24.3), id. Burukovsky, USNM 21147; 0 5o 36`N/ 86o56´W, coll. USFC, North Pacific Ocean, 245m, 0 4 males (21.7–23.2), 0 4 females (24.1–25.6), id. Burukovsky, USNM 21146; 0 7o 09´N/ 80o50`W, North Pacific Ocean, 588 m, coll. USFC, 6 females (14.3–17.2), 3 males (15.1–15.7), id. Burukovsky, USNM 21114; 0 7o 06´N/ 80o34´W, 1271m, coll. USFC, 1 male (20.3), 1 female (22.8), id. Burukovsky, USNM 21143.

Description. Body moderately slender; integument moderately hard, not membranous, surface smooth, shiny. Rostrum proximally horizontal, distally it slightly rises up; rostrum length 70–96%, in the extreme case up to 120%, of carapace length (Figs. 2 A–F; 3A, F–H); distance from rostrum apex to the rostrum distal dorsal tooth is a half of rostrum length; rostrum dorsal margin (including postrostral crest) with 19–36 (usually 23–32) tightly fitting teeth; number of teeth on rostrum dorsal margin and on the postrostral crest do not present ontogenetic variability and has no sexual dimorphism; rostrum ventral margin with 1–5, usually 3–4 teeth, lying in the region of the rostrum free of dorsal teeth (Figs. 2 A–F; 3A, F–H).

Eyes normally developed, its width is noticeably larger than the diameter of the eye stalk.

Posterodorsal margin of third abdominal somite poorly developed. Continuation of its sides when crossing forms an obtuse angle close to 90° (Figs. 2 G, 3C). Fifth abdominal somite pleura with its sides intersecting at an angle with less than 90° (Fig. 2 H); armed with a little spine whose axis coincides or nearly coincides with the bisector of the angle in adult specimens (carapace length of 15mm or more), in small shrimps the lower margin of the pleura is rounded and the spine is absent (Fig. 2 I–L, 3B). Tubercles, rollers and other elevation on the inner surface of the anterior margin of the pleura of the fifth abdominal somite are absent.

First pereopod merus with 0–3 (usually one), ischium with 1–3 (usually 2) spines. Second pereopod ischium with one subdistal spine. Third pereopod ischium with 0–3 (usually one) spines. Fourth and fifth pereopods usually unarmed.

Distoventral organ at sixth abdominal somite formed by two single parallel rows of setae that begins with long plumose setae and at the proximal third of sixth abdominal somite length turns to short spindle shaped setae (not plumose) that extends to more than a half of spots length (Figs. 2 N–P; 3D; 4A–C); spots located at the sideways surface of sixth abdominal somite; spots more or less oval or teardrop shaped; spots length not more than 1.5 times its width, distance between them 2–2.5 times its width (Figs. 2 O, 3D).

Telson with 6–9 (usually 7–8) pairs of dorsolateral spines; usually with one accessory spine, occasionally specimens with two or without accessory spines can be found (Figs. 2 M, 3E).

Distribution. In the Northeastern Atlantic N. gracilipes occurrence can be divided into 3 areas. The most western is Azores, where N. gracilipes is limited by coordinates 39°25'– 37°49'N and 42°45'– 22°30'W, at depths ranging from 815 to 1240 m. The second area is the Ibero-Moroccan, along the western Spain and African continent, from 36°48'N / 09°28'W to 28°13'N / 9°55'W, including the Mediterranean Sea, at depths between 859 and 1590 m. Finally, the Cape Verde Islands area (16°53'– 15°15'N /25°12'– 22°30'W, from 598 to 660 m depth) (Burukovsky 2009; 2012; Crosnier and Forest 1973) (Fig. 11).

At South Atlantic Ocean N. gracilipes is recorded at 00°26´N / 17°03´W (902m) and at 15°08’S / 38°40’W (1026m) (Fig. 11).

In the Eastern Pacific N. gracilipes is found from Southern California (24º58'N) to the Galapagos Islands (01º21'S) and Peru (09º57'S) (Fig. 11) at depths from 190 to 1860 m (Burukovsky 2001b; 2012).

Remarks. Four Nematocarcinus species present the rostrum extending to more than a half scaphocerite length, and rostrum dorsal margin without teeth in a half or more of its length: N. agassizii Faxon, 1893; N. gracilipes; N. machaerophorus Burukovsky, 2003 and N. tenuirostris Spence-Bate, 1888. Among this four species the last two can be easily distinguished by N. gracilipes by the distoventral organ of the 6th abdomen segment that is at one special blister (Burukovsky 2012).

A detailed comparison of the morphology of N. gracilipes and N. agassizii was done herein: The rostrum shape (including the ontogenetic variability, Fig. 2 B–F) of these two species is very similar. Variations in rostrum length and in the number of dorsal and ventral teeth are overlapping and also cannot be used to distinguish these two species (Table 1).

Besides that Dr. Cardoso examination of N. agassizii material deposited in the National Museum of Natural History (Washington, USA) showed that the figure of the distoventral organ at the sixth abdominal somite of this species made by Dr. Burukovsky (Burukovsky 2001b; 2003; 2012) is incorrect. In fact, its structure is only slightly different from the structure of this organ in N. gracilipes (Figs. 2 N, O; 3D). Furthermore, Dr. Lemaitre, at our request, investigated the structure of the bristles of the distoventral organ in the lectotype and some paralectotypes of N. agassizii, and found: “I have looked at the lectotype of Nematocarcinus agassizii Faxon, 1893 (USNM 291472), and it has a row of simple setae at least on one side of the ventral face of the 6th abdominal somite (most setae seem to have fallen off). I have also examined a few of the paralectotypes (USNM 21233), and most have the same kind of simple setae, although some lack or have few setae and perhaps have also fallen off. The setae are definitely not plumose ”. As previously found by Burukovsky (2009) the bristles of distoventral organ in N. gracilipes present some exclusive features: not plumose, spindle shaped simple setae (Figs. 2 P, 4A–C). These exclusive features totally coincide with the material of N. agassizii examined by Dr. Lemaitre and herein.

Considering that all other diagnostic features of these two species coincide, almost coincide or overlap each other (Table 1) we conclude that Nematocarcinus agassizii Faxon, 1893 is a junior synonym of N. gracilipes Filhol, 1884. All differences previously described between these two species can be considered belonging to the population level. This synonymy allows increasing in the distribution area of N. gracilipes. In this way, there is none endemic species of Nematocarcinus genus on the continental slope of the eastern Pacific.