Coalecerotanais alter Błażewicz-Paszkowycz, Bamber & Cunha, 2011, sp. nov.

Coalecerotanais alter sp. nov.

Figs 11–13

Material. 1 specimen, Holotype (BMNH.2010.402), 5 specimens, paratypes (BMNH.2010.403-407), Station CA 546, Captain Arutyunov mud-volcano, 35º39.692’N 07º20.046’W, 1345 m depth, mud breccia and gas-hydrate, TV-grab, 0 6.08.2004, coll. MRC.

Other records. 7 specimens, same data as holotype; 2 specimens, Station CA 547, Captain Arutyunov mudvolcano, 35º39.701’N 07º20.037’W, 1344 m depth, mud breccia and gas-hydrate, TV-grab, 0 6.08.2004, coll. MRC.

Description. Body (Fig. 11 A, B) small even for a tanaidomorph, holotype 0.65 mm long, 5.3 times as long as wide. Cephalothorax subrectangular, as long as wide, almost as long as pereonites 1 and 2 together, naked, eyes and eyelobes absent. Five free pereonites, all laterally convex, naked; pereonite 1 shortest, pereonites 2, 3 and 5 subequal, 1.64 times as long as pereonite 1, pereonite 4 longest, twice as long as pereonite 1, pereonite 6 absent (all pereonites respectively 2.8, 1.9, 1.7, 1.5 and 1.7 times as wide as long). Pleon naked, cylindrical, 1.6 times as long as wide; all pleonites and pleotelson fused, with no indication of sutures, and no pleopods.

Antennule (Fig. 12 A) relatively stout, of four articles, proximal article 1.33 times as long as wide, 0.7 times as long as distal three articles together; second article as long as wide, half as long as first article, with single outer distal seta; third article just shorter than second, slightly longer than wide, with single inner and outer distal setae; fourth article 1.6 times as long as third article, 2.5 times as long as wide, with inner subdistal seta and three distal setae, and with suggestion of fused articulation (of a fifth article) at origin of subdistal seta.

Antenna (Fig. 12 B) of six articles, proximal three articles compact, naked; first and second articles of equal length, third article 1.5 times as long as second; fourth article longest, twice as long as third, with one ventrodistal seta; fifth article two-thirds as long as fourth, with one distal seta; sixth article half as long as third article, with two subequal distal setae.

Labrum not recovered. Mandibles not found. Maxillule (Fig. 12 D) with seven distal spines, palp short, with two distal setae. Maxilla (Fig. 12 D) ovoid, naked. Maxilliped palp (Fig. 12 C) first article naked, second article with one outer and two inner setae, third article with four inner setae on slight apophysis, fourth article with five distal setae; endites simple, naked.

Cheliped (Fig. 12 E) with subcircular basis as long as wide, with mid-dorsal seta; merus subtriangular with single ventral submarginal seta; carpus 1.5 times as long as wide, with one dorsodistal and two midventral submarginal setae; propodus 1.2 times as long as wide, with one mid-distal seta; fixed finger with two ventral setae and two setae on cutting edge, distal half of cutting edge crenulate; dactylus overreaching fixed finger, with one seta.

Pereopod 1 (Fig. 13 A) coxa naked; basis slender, 3.6 times as long as wide, naked; ischium conspicuous, with one ventrodistal seta; merus 0.75 times as long as carpus, with slender ventrodistal seta; carpus 1.5 times as long as wide with three distal setae; propodus as long as carpus and merus together, with one ventral subdistal seta; dactylus with distinct, slender and slightly longer unguis, both together 1.3 times as long as propodus. Pereopod 2 (Fig. 13 B), similar to but less attenuate than pereopod 1, basis 2.9 times as long as wide; carpus 1.2 times as long as wide. Pereopod 3 (Fig. 13 C) as pereopod 2.

Pereopod 4 (Fig. 13 D) stouter than anterior pereopods, basis 2.4 times as long as wide; merus just longer than carpus, merus with two short, curved ventrodistal spines; carpus with three short, curved ventrodistal spines; propodus 0.83 times as long as carpus, with two short, curved ventrodistal spines and one stout dorsodistal spine; dactylus and much shorter unguis partially fused into a claw, 1.2 times as long as propodus. Pereopod 5 (Fig. 13 E) as pereopod 4.

Pleopods absent.

Uropod (Fig. 13 F) uniramous, basis as long as wide, naked; endopod of one segment nearly four times as long as wide, with five distal setae.

Etymology. from the Latin, alter –other, thus alternate, this being the second recorded species of this strange genus.

Remarks. This genus is recognizable as being the only one currently described in which the sixth pereonite and pereopod are absent. Larsen (2003) presumed the sixth pereonite to be fused with the pleon, but it may be that it never develops from the manca, a neotonous feature known to occur in some genera of the anthurid isopods (e.g. Colanthura Richardson, 1902), although in their case to extreme reduction rather than complete absence.

The generotype, and only other know species of the genus, Coalecerotanais inflatus Larsen, 2003, was also recorded from a chemically-reduced habitat, a deep-sea (570 m) cold-seep in the Gulf of Mexico. Coalecerotanais alter sp. nov. shows numerous similarities to C. inflatus, notably the spination of the pereopods, the morphology of the antennule and uropods, and the gross appearance of the body, although C. inflatus has more convoluted lateral margins to its pleonites.

By contrast, C. alter is distinguished from C. inflatus in being smaller and less slender, with a less attenuate pleon. The antennule of C. inflatus has penicillate rather than simple setae on the second and third articles, and is without the suggestion of a fused fifth article; the antenna of C. inflatus has a seta on the second article but none on the fifth, and the distal setae on the sixth article are extremely unequal (equal in length in C. alter). Coalecerotanais alter has more distal spines on the maxillule endite and more setae on the maxilliped palp articles; the fixed finger of the chela has two ventral setae (none in C. inflatus), the merus of pereopod 3 and the ischium of pereopods 3 to 5 have a ventrodistal seta (none in C. inflatus), and the carpus and propodus of all pereopods have more setae/ spines than do those of C. inflatus.

The mandibles of Coalecerotanais inflatus, as those of Spinitanaopsis insolituchelia (see above) were also found to be almost completely reduced, with no lacinia mobilis or molar process (Larsen 2003). Mandibles were not found in the present material; either they are so reduced as to be indistinguishable as distinct structures, or they may be absent.

The species was collected from the Captain Arutyunov mud-volcano (type-locality) in the deep-water field within the Portuguese margin, at depths from 1344 to 1345 m on muddy-substrata with gas-hydrate present. This highly aberrant genus may prove to be endemic to vent/seep habitats.