Plesionika ensis A. Milne Edwards 1881

Plesionika ensis (A. Milne Edwards, 1881)

(Figs. 3, 4)

Acanthephyra ensis A. Milne Edwards, 1881: 14; Young, 1900: 476. Pandalus ensis – A. Milne Edwards, 1883: pl. 18; Faxon, 1896: 161; Alcock, 1901: 96; Coutiére, 1905: 675; Rathbun, 1906: 914.

Plesionika uniproducta Bate, 1888: 641, pl. 113, fig. 1 (part); Moreira, 1901: 8 (part). Plesionika semilaevis Bate, 1888: 664 (part).

Plesionika ensis – De Man, 1920: 106; Holthuis, 1951: 55, fig. 10; Crosnier & Forest, 1968: 1138; 1973: 209, figs. 63c, 64f; Pequegnat, 1970: 94; Omori, 1971: 241; Cabral et al., 2000: 246; Cruz & Fransen, 2004: 141; Viana et al., 2007: 36.

Material examined: REVIZEE: E- 0 500, 13o22’S, 38o40’W, 394 m, 1 male (12 mm), 1 ovigerous female (14 mm), MNRJ 14668; E-0513, 15o53´S, 38o02´W, 489 m, 4 males (13–15 mm), 1 female (13 mm), 3 ovigerous females (13–14.5 mm), MNRJ 14658; E-0518, 13o21’S, 38o38’W, 518 m, 1 male (21 mm), 1 female (17 mm), MNRJ 14660; D- 0 464, 21o48´S, 40o01´W, 618 m, 1 male (13.5 mm); MNRJ 13735.

Description: Rostrum long, curved downwards in proximal region, and upwards beyond antennular peduncle; far overreaching scaphocerite, 2.3–2.6 (avg. 2.4, n=6) times as long as carapace; ventral margin with 40–51 (avg. 43, n=6) teeth closely disposed, dorsal margin with one to three (avg. 2, n=11) large teeth well spaced, reaching antennular peduncle end, one distal tooth and two to three post-rostral teeth the proximal one variably movable; eye large, spherical, with ocellus; strong antennal and small pterygostomian spines present; carapace smooth (Fig. 3 A). Stylocerite straight at base and tapering only near the triangular apex, not overreaching the distal margin of first antennular peduncle article (Fig. 3 B). Scaphocerite 0.94–1.05 (avg. 0.99, n=12) as long as carapace, with blunt apex, distal tooth strongly overreaching blade (Fig. 3 C). Maxilliped III with epipod, penultimate segment 0.76–0.93 (avg. 0.84, n=13) times longer than terminal segment. Pereopods 1–4 with epipod, pereopod 5 without epipod. Pereopod 2 chelate, equal in size (Fig. 3 D, E), carpus with 15–28 (avg. 17, n=12) articles. Pereopod 3 overreaching scaphocerite with propod distal third; propod 0.45–0.55 (avg. 0.48, n=10) times as long as carapace; 4.3–7.6 (avg. 5.8, n=11) times longer than dactyl (Fig. 4 A), dactyl with two stout setae (Fig. 4 B). Dorsal surface of abdominal somite 3 with a straight spine; pleura of somite 3 rounded, pleura of somite 4 triangular but not acute, pleura of somite 5 triangular and acute (Fig. 4 C). Telson 0.72–0.92 (avg. 0.77, n=13) times as long as abdominal somite 6; not sulcate in dorsal midline, with three pairs of dorsolateral stout setae, and three pairs of stout distal setae (Fig. 4 D).

Distribution: Western Atlantic: Florida, Gulf of Mexico, Antilles, Brazil (Maranhão, Paraíba, Alagoas, Bahia, Rio de Janeiro). Eastern Atlantic: Senegal, Gabon, Congo, Angola. Indian and Pacific: Andaman Sea, Arabian Sea, Hawaii, Fiji. Adults in Atlantic founded in depths from 230 to 732 m, in Indo-West-Pacific in depths from 101 to 1251 m, the shallowest record is in Hawaiian waters at 55 m (modified from De Man, 1920; Crosnier & Forest, 1973; Cabral et al., 2000).

Remarks: Working with material from Brazilian waters (9o05`N / 34o50`W, Alagoas), collected by the Challenger Expedition, Bate (1888) described Plesionika uniproducta based on two specimens, one male and one female. According to Crosnier & Forest (1973), the female is actually P. e n s i s and the male is actually Plesionika martia (A. Milne Edwards, 1883). In this way, Bate (1988) was the first to record P. e n s i s and P. martia to Brazilian waters, both identified as P. uniproducta.

According to Chan & Crosnier (1997) Plesionika ensis is in a group together with Plesionika reflexa Chace, 1985. These species are very similar as pointed by Chace (1985), Crosnier (1986), Chan & Crosnier (1997) and Fransen (2006). Chace (1985) compares the type series of P. reflexa with specimens identified as P. e n s i s from various parts of the world and gives several characters that might prove to be of specific significance. The proportional length of dactyl and propod of pereopod 3 being 0.17–0.25 in the 14 specimens of P. e n s i s from western Atlantic and 0.30–0.46 in P. reflexa from South China Sea and Philippines; in the Brazilian material this proportion is 0.13–0.23, with the average of 0.18 (n=11) fitting with the range of western Atlantic P. e n s i s. Populations of P. e n s i s from East Atlantic, however, have a similar ratio (0.26–0.40), as P. re f l e x a material cited above (Chace, 1985; Fransen, 2006). In Hawaiian material of P. e n s i s there are two forms, one with a very short dactyl (0.12–0.16) and other with a range intermediate (0.21–0.30) between that of the western and Eastern Atlantic populations (Chace, 1985).

Other feature cited by Chace (1985) as useful to distinguish both species is the dorsal spine on abdominal somite 3 with a tendency to recurve upwards in P. reflexa, whereas no such inclination has been noticed in typical form of P. e n s i s. Chan & Crosnier (1997) mentioned that the absence of any specimen with a recurved dorsal spine in the Atlantic is sufficient reason to not synonymize P. reflexa with P. e n s i s. In the 13 Brazilian specimens examined herein the dorsal spine on abdominal somite 3 is straight (Fig. 4 C).

The scaphocerite distal tooth also may be of taxonomic importance, in P. reflexa it slightly overreaches blade, while in P. e n s i s it strongly overreaches blade (Chace, 1985; Fransen, 2006), as was observed in Brazilian material (Fig. 3 C). Chan & Crosnier also pointed that the western Atlantic population of P. e n s i s presents a rostrum 2.2–2.8 (avg. 2.5) times carapace length, with 35–48 ventral teeth (avg. 42, n=6). The material herein examined fits in this range, with rostrum 2.3–2.6 (avg. 2.4, n=6) times as long as carapace and ventral margin with 40–51 teeth (avg. 43, n=6).

Chan & Crosnier (1997) comment that many more species may be also present in the material now identified as P. e n s i s and P. reflexa (as occur with the great diversity of species contained in the “ P. m a r t i a (A. Milne Edwards, 1883)” (Chace, 1985) and “ P. narval (Fabricius, 1787) ” (Chan & Crosnier, 1991) groups). Or the problem of these two species may be similar to the case of P. e d w a rd s i i and P. crosnieri, in which both species are distributed in the Indo-Pacific but only one occurs in the Atlantic (Chan & Yu, 1991; Chan & Crosnier, 1997).