Nematocarcinus agassizii Faxon 1893

Nematocarcinus agassizii Faxon, 1893

Figures 1, 2 A, 3, 4A, 5A–C

Nematocarcinus agassizii Faxon, 1893: 204; 1895: 158, pl. 42; Del Solar 1972: 9; 1987: 79, fig. 7; Méndez 1981: 76, pl. XXXIV, figs. 255–257; Wicksten 1989: 312; 1991: 154; Burukovsky, 2001: 1432, fig. 3. Vélez et al. 1992: 7, textfig. 5; Wicksten & Hendrickx 1992: 7 (list); 2003: 59 (list); Hendrickx 1993: 307 (table); 1995: 454 (key), fig. 1, 455, textfig.; 1996: 946; 2005: 163; Kameya et al. 1997: 20; 1998: 89 (list); Moscoso 2012: 42.

Nematocarcinus gracilipes. Cardoso & Burukovsky 2014: 440 (part; records from the eastern Pacific).

Characteristics. Rostrum distinctly longer than carapace in males (1.06 times CL; n = 10), shorter in females (0.86 CL; n = 10), elongate, almost horizontal from its base to 2/5 of its length, remaining portion without dorsal teeth and gently curved upwards, ending in a sharp point, numerous closely set teeth (23–32) (up to 38 in material examined; n=10) on the dorsal margin in proximal 1/3 to 1/2 of its length; 3–4 ventral teeth in the distal half. Flagella of both antennas long, that of antennule almost twice the antennal flagellum length and more than twice the length of the whole body. Antennal scale with lamella distally truncated. Spines on pereiopods 1–5 as follows: first pereiopod, ischium 2, merus 1; second, ischium 2, merus 1; third, ischium 1, merus 5 + 7; fourth, ischium 1, merus 4 + 4; fifth, ischium 1, merus 3 + 5. Carpus of all pereiopods without spine. Pereiopods 3–5 greatly elongate, of about the same length, carpus of these legs 5–7 length of propodus, combined length of ischium, merus and carpus about 4 times as long as carapace length. Third pleomere with posterodorsal margin of tergum somewhat extended over fourth pleomere, tip of margin rounded. Pleura of fifth pleomere without bump on inner sides, ending in a sharp spine curved slightly downward. Spots of ventral organ of sixth pleomere small, hardly discernible, kidney-shaped, slightly narrowing forward, 2–2.5 times as long as wide, distance between the spots about 2.1 times spots width (n = 10); setal pits arrange in single line on each side, nearly parallel. Length of telson barely exceeding length of sixth pleomere in females (telson/6th pleomere ratio, 1.05; n = 10), proportionally longer in males (telson/6th pleomere ratio, 1.21; n = 10), armed with 7 pairs of dorsolateral spines, and 3 pairs of spines on posterior tip (modified and completed from Burukovsky 2003, 2013) (Figures 1, 2 A, 3, 4A, 5A–C).

Colour. Crimson red (Figure 2 A).

Material examined. TALUD XV, St. 1 (23º18’40”N; 111º19’37” W), Ago 4, 2012, 10 M (CL 21.51–25.42 mm), 4 F (CL 20.49–24.74 mm), 26 OF (CL 23.32–31.21 mm), BS, 750–850 m (ICML-EMU-10773, 10787); St. 24 (27º05’42”N; 114º35’30”W), Ago 1, 2012, 34 M (CL 18.36–27.04 mm), 4 F (CL 20.48–25.39 mm), BS, 772– 786 m (ICML-EMU-10774); TALUD XVI–B, St. 5 (28º48’N; 115º24’06”W), May 24, 2014, 16 M (CL 13.59– 27.89 mm), 35 F (CL 13.59–29.61 mm), 17 OF (CL 27.23–30.22 mm), BS, 772–776 m (ICML-EMU-10775, 10788); St. 7 (20º21’12”N; 115º39’08”W), May 31, 2014, 2 M (CL 14.28–14.95 mm), 4 F (CL 13.75–16.38 mm), 1 OF (CL 28.56 mm), BS, 750– 710 m (ICML-EMU-10776); St. 10 (29º07’50”N; 116º15’30”W), May 30, 2014, 2 M (CL 12.03–21.34 mm), 4 F (CL 20.79–28.96 mm), 4 OF (CL 29.03–31.90 mm), BS, 860–910 m (ICML-EMU- 10777, 10789); St. 23 (30º56’24”N; 116º40’45”W), May 27, 2014, 1 M (CL 23.48 mm), 1 F (CL 21.10 mm), BS, 1296–1340 m (ICML-EMU-10778).

Additional material examined. Lectotype USNM 291472 (ex 21233). R/V "Albatross" St. 3358, Coiba Island, Panama, February 24, 1891. Paralectotypes: 1 ovigerous female, CL 29.4 mm, USNM 21233, and 2 ovigerous female, CL 30.1 and 34.5 mm, USNM 21152.

Geographical distribution. From off Ahome, Sinaloa, Mexico, to Mancora Bank, Peru; Coco (del Coco) (Costa Rica), Malpelo (Colombia) and Galápagos (Ecuador) islands (Wicksten & Hendrickx 2003). Based on the material examined, the distribution of N. agassizii extends to the west coast of the Baja California Peninsula (Figure 6). The Scripps Institution of Oceanography invertebrates collection contains one lot of Nematocarcinus agassizii (Id. M.K. Wicksten) (C-10435) captured by the R/V "New Horizon" (ROSA cruise, March 24, 1993) in 503–795 m depth, at 30º36.36'N, 117º12.14'W.

Remarks. While reviewing species of Nematocarcinus collected in the southwestern Atlantic, Cardoso & Burukovsky (2014) compared material of N. gracilipes Fihol, 1884 with that of N. agassizii and came to the conclusion that the latter is a junior subjective synonym of the former. They pointed out that N. agassizii and N.

gracilipes are very similar and the only two species within the genus featuring a distoventral organ of the sixth pleomere with non-plumose, spindle-shaped setae. In their account of N. gracilipes, Cardoso & Burukowsky (2014) noted: "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 spot length". The lectotype (USNM-291472) and paralectotypes (USNM-21233 and 21152) of N. agassizi were carefully examined during our study (Figures 3, 4 A, 5A–C). None of the specimens examined has ventral splindle-shaped setae on the sixth pleomere as illustrated by Cardoso & Burukovsky (2014) for N. gracilipes, reproduced herein (Figure 4 B, C). Instead, all setae are long, slender, and those in the middle part of the somite are similar to those found on the distal and proximal section of the somite, although slightly different in length (Figures 3, 4 A, 5A, B). Moreover, all the setae are plumose (Figures 4 A, 5 B), although in some cases many setules have been lost and setae might appears as non-plumose at first glance. In several cases, however, setules are clearly visible under high magnification (Figure 5 B). In addition to the slight differences observed in the structure of the distoventral organ between the two species (see Cardoso & Burukovsky, 2014), we believe that the clear difference of setae type (both in shape and in size) between N.agassizii and N. gracilipes is sufficient to reinstate N. agassizii as a valid species. In addition to the morphology, the disjunct distribution between the two remote populations would seem to suggest that they are specifically distinct. As in other closely resembling species with allopatric or almost allopatric distribution, a comparison of genetic material based on freshly collected material of both species is highly desirable to define how close they are and how they relate to other species within the genus.

Despite of the numerous samples available, N. agassizii was not collected during the present survey within the Gulf of California and only N. faxoni was found in that area (see below). Therefore, any material from the Gulf of California available in collections and identified as N. agassizii should be carefully re-examined.