Pseudomma bellingshausensis Vicente, 2011, n. sp.

Pseudomma bellingshausensis n. sp.

(Figs.1–3)

Type locality Station 34TA, Bellingshausen Sea, 70º06’24”S – 84º52’14”W, 612 m depth, 10–50 cm water layer above bottom, sediment with a low organic matter content (1.8%) and a high percentage of fine sand (59.9%), 31 January 2006.

Material examined. Holotype (ICMM /2010/10/001). Mature male (11.2 mm TL).

Paratypes (ICMM /2010/10/002). Mature female (10.0 mm TL), 4 mature females (3.2 mm CL, 3.5 mm CL, 3.0 mm CL, 3.0 mm CL), 2 mature males (3.5 mm CL, 3.5 mm CL), 11 immature females (9.4 mm TL, 8.1 mm TL, 7.8 mm TL, 3.0 mm CL, 2.9 mm CL, 2.8 mm CL, 2.7 mm CL, 2.7 mm CL, 2.5 mm CL, 2.5 mm CL, 2.2 mm CL), 3 immature males (10.3 mm TL, 9.4 mm CL, 2.6 mm CL) and 13 juveniles (5.5 mm TL, 2.2 mm CL, 2.0 mm CL, 1.8 mm CL, 1.8 mm CL, 1.8 mm CL, 1.7 mm CL 1.7 mm CL, 1.7 mm CL, 1.7 mm CL, 1.6 mm CL, 1.5 mm CL, 1.5 mm CL). Station 34TB, same locality, 55–95 cm water layer above bottom: 1 mature male (3.0 mm CL), 1 mature female (2.8 mm CL) and 1 immature male (2.8 mm CL). Station 34TC, same locality, 100–140 cm water layer above bottom: 2 immature females (3.1 mm CL, 3.0 mm CL) and 3 juveniles (7.4 mm TL, 4.4 mm TL, 2.2 mm CL).

Diagnosis. Antero-lateral margins of ocular plates serrated with 22 conspicuous serrations. Posterior part of telson armed with eight pairs of spiniform setae that increase in size distally.

Description. The morphological characteristics refer to both sexes, unless otherwise stated. Carapace with anterior margin evenly rounded and anteriorly produced lateral corners; posterior margin emarginated dorsally, leaving last thoracic somite partially uncovered; posterolateral lobe covering anterior half of abdominal somite. Ocular plate extending to mid-portion of first segment of antennular peduncle; plate with well-marked median anterior cleft; antero-lateral margins serrated with 22 serrations (Fig. 1 A).

Antennular peduncle half as long as antennal scale. First article wider than long, without ventral carina, outer distal corner armed with two setae; second article short, one fourth as long as broad, armed with one seta on the distal end of outer margin; third article slightly longer than broad, armed with one seta near the distal end of outer margin, third segment of male peduncle supporting a large and hirsute appendix masculine (Fig. 1 A).

Sympod of antenna with outer distal angle produced into a long acute process. Peduncle extending slightly beyond the antennular peduncle; first article short as long as broad, with the inner proximal margin rounded; second article half as long as broad, inner distal margin armed with three setae; third article longest, twice as long as broad, distal inner margin armed with three setae. Antennal scale four times as long as maximum width, extending for half of its length beyond the antennular peduncle; outer margin straight, smooth, terminating in strong triangular process, apex extends beyond terminal spine, without apical suture (Figs. 1 A, B).

Labrum almost oval, wider than long, posterior margin with two distinct areas consisting of a cluster of short setae and an area covered with small scalelike protrusions (Fig. 1 C).

Mandibles well developed; three-segmented palp, second article bottle-shaped with setae on both margins, about twice as long as third; third article armed on distal two-thirds of inner margin with eleven ventral spinose setae and one distal large conspicuous seta. Spine row with three and eight spines on left and right mandible, respectively (Figs. 1 D, E)

Maxillule basis (outer lobe) apex armed with seven cuspidate setae and three setae on ventral surface; coxal endite (inner lobe) with nine plumose setae, the two apical and one posterior are large; proximal anterior margin of basis with a row of small setae (Fig. 1 F).

Maxilla with distal article of endopod oval, longer than wide, margins densely setose on distal two thirds; exopod relatively slender, extending to the distal margin of proximal article of endopod, with 16 setae on lateral margin and two larger distal setae; lateral margin of coxa armed with one row of setae (Fig. 2 A).

First and second thoracic appendages formed as maxillipeds. First thoracopod with well developed endite armed with six large setose setae and a row of small setae on the inner side of the basis; ischium with ten pappose setae on inner margin; merus and carpus subequal in length, armed with a row of small setae on outer margins; merus with nine pappose setae on its inner margin; carpus with two rows of nine and seven setae on its inner margin and two outer distal setae; propodus with a row of small setae and two long setae on its outer margin and seven setae distally; dactylus with one distal nail (Fig. 2 B).

Second thoracopod robust longer than the first, endopod armed with a row of small setae on its outer margins; well developed endite armed with two apical large and setose setae; preischium, ischium and merus short; carpus and propodus longer; dactylus densely setose (Fig. 2 C).

Third thoracopod with endopod long and slender, forming minute chelate structure terminally, surrounded by crown of setae (Fig. 2 D). Fourth to eighth thoracic appendages particularly fragile, broken off in all individuals examined. Male genital organ bearing one apical seta and a row of small setae on its posterior margin (Fig. 2 E).

Pleopods of male developed, biramous, endopods with side lobe developed. First pleopod with unsegmented endopod and 9-segmented exopod. Second to fourth pleopods with exopods and endopods sub-equal in length; 7- segmented exopods and 6–7segmented endopod; fifth pleopod with 7-segmented exopod and 4-segmented endopod, exopod longer than endopod (Figs. 3 A-E). Pleopods of the female uniramous, unjointed, increasing in length towards posterior pairs (Figs. 3 A–H).

Endopod of uropod slender, extending beyond apex of telson for 1/5 of its length, armed on inner margin near statocyst with five short pappose setae and one strong setae, outer proximal margin of endopod armed with six short pappose setae dispersed among longer setae (Fig. 3 J); exopod longer than endopod

Telson linguiform, two times as long as broad at base; lateral margins unarmed; posterior part armed with eight pairs of spinose setae which increase in size distally; apex armed with two median thin and fragile setae (broken off in almost all individuals examined, but visible at its base) (Fig. 3 I).

Colour in live specimens. White tegument with red pigmentation irregularly distributed on the body and appendages.

Etymology. This species is named for its present known distribution.

Remarks. Pseudomma bellingshausensis bears resemblance to two species described from the North Atlantic waters: P. j a s i Meland and Brattegard, 1995 from the Faroe Island and Iceland Basin and P. islandicum Meland and Brattegard, 2007 from the eastern Iceland Basin. The new species can easily be distinguished from these two North Atlantic species by the telson armature and the serration of the ocular plates. The telson of P. bellingshausensis being armed with 16 spinose setae, whereas in P islandicum the distal third of the telson is armed with six to 11 setae. In P. j a s i the telson is armed with a densely set of 20 distal setae. The new species can also be distinguished from P. j a s i by the serration of the antero-lateral margins of the ocular plates (minuted serrated versus quite conspicuous serration in P. bellingshausensis).

Regarding Antarctic species of the genus, the new species is easily distinguished from P. a r m a t u m and P. belgicae by the ocular plate serration (without serrated margin in both species) and from P. sarsi, P. longicaudum and P. schollaertensis by the telson lateral margin armature (with lateral setae in these three species). The new species can be distinguished from P. a n t a rc t i c u m by the apex of the telson (armed with eight pairs of setae versus three or four pairs in P. antarcticum) and the shape of mandibles, maxilla and male pleopods.

The morphological affinity between the new species and P. j a s i and P. islandicum supports Meland (2004) hypothesis on a common ancestry and recent divergence between Antarctic and North Atlantic deep-sea mysids.

Affinities to the new species P. melandi is also noted and discussed later.