Pseudomma melandi Vicente, 2011, n. sp.

Pseudomma melandi n. sp.

(Figs. 4–7)

Type locality Station 31TA, Bellingshausen Sea, 69º57’49”S – 86º22’23”W, 1395 m depth, 10–50 cm water layer above bottom, sediment with a medium organic matter content (5.3%) and a high percentage of mud (72.2%) and fine sand (20.7%), 28 January 2006.

Material examined. Holotype (ICMM /2010/10/003). Immature female (15.7 mm TL).

Paratypes (ICMM /2010/10/004). Two immature males (5.2 and 4.0 mm CL), 3 immature females (10.8 mm TL, 4.6 mm CL, 3.6 mm CL) same locality.

Diagnosis. Antero-lateral margins of ocular plates serrated with 8 conspicuous serrations. Posterior part of telson armed with five pairs of setae which 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. First five segments of abdomen subequal in length; sixth somite about twice the length of the fifth (Fig. 4 A).

Ocular plate extending to mid-portion of first segment of antennular peduncle; plate with well-marked median anterior cleft; antero-lateral margins serrated with eight serrations (Fig. 4 B).

Antennular peduncle half as long as antennal scale. First article wider than long, with a medial ventral carina, outer distal corner armed with three setae; second article short, one half as long as broad, armed with three setae on the inner margin, the distal one very conspicuously plumose; third article slightly longer than broad, armed with six spinose setae on the inner margin, third segment of immature male peduncle supporting an incipient appendix masculine (Fig. 4 C).

Sympod of antenna with outer distal angle produced into a long acute process. Antennal and antennular peduncles subequal in length. First article of antennal peduncle shorter, as long as broad, with the inner proximal margin rounded; second and third articles subequal in length; inner distal margin of second article armed with two spinose setae and one non-spinose setae; third article distal margin armed with three spinose setae and seven non-spinose setae. Antennal scale five times as long as maximum width, extending for one third of its length beyond the antennular peduncle; outer margin straight, smooth, terminating in strong triangular process, apex extended slightly beyond terminal spine, without apical suture (Figs. 4 B, D).

Labrum almost oval, wider than long, posterior margin with two distinct areas consisting of two clusters of short setae and an area covered with small scalelike protrusions (Fig. 5 C).

Mandibles well developed; three-segmented palp, second article about twice as long as third; third article setose along margins and armed with one distal large conspicuous seta. Spine row with nine and three spines in right and left mandibles, respectively (Figs. 5 A, B).

Maxillule basis (outer lobe) apex armed with nine cuspidate setae; coxal endite (inner lobe) with five apical plumose setae and two shorter non-plumose posterior setae; proximal anterior margin of basis with a row of small setae (Fig. 5 D).

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 19 setae on lateral margin and two larger distal setae (Fig. 5 E).

First thoracopod formed as maxilliped; with well developed endite armed with nine large setose setae and a row of small setae on the inner side of the basis; ischium with nine pappose setae on inner margin; merus shorter than carpus, armed with eight pappose setae on its inner margin and four pappose setae on outer margin; carpus with two rows of nine and five setae on its inner margin and one outer distal seta; propodus with three and seven setae on its inner and outer margin, respectively; dactylus densely set with setae and armed with one distal nail (Fig. 6 A). Second to eighth thoracic appendages particularly fragile, broken off in all individuals examined.

Pleopods of male developed, biramous, endopods with side lobe developed. First pleopod with unsegmented endopod and 11-segmented exopod. Second to fourth pleopods with exopods and endopods sub-equal in length; 11-segmented exopods and 11–12 segmented endopod; fifth pleopod with 10-segmented exopod and 7-segmented endopod, exopod longer than endopod (Figs. 6 B–F). Pleopods of the female uniramous, unjointed, increasing in length towards posterior pairs (Figs. 7 A–E).

Endopod of uropod slender, extending beyond apex of telson for 2/3 of its length, armed on inner margin near statocyst with four to six short pappose setae and one strong seta (Fig. 7 H), outer distal margin of endopod armed with five short pappose setae (Fig. 7 F); exopod longer than endopod.

Telson linguiform, one and half times as long as broad at base; lateral margins unarmed; posterior part armed with five pairs of spiniform setae which increase in size distally; apex armed with two median thin setae (Figs. 7 F,G).

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

Etymology. This species is named in honour of Dr. Kenneth Meland in recognition of his contribution to the knowledge of the genus Pseudomma.

Remarks. Pseudomma melandi bears some resemblance to P. j as i Meland and Brattegard, 1995, described from North Atlantic waters. The new species can easily be distinguished from P. j a s i by the shape of the antennal scale, the telson armature and the serration of the ocular plates. The apex of the antennal scale extends clearly beyond the outer margin spine in P. j a s i, whereas in P. melandi the apex extends slightly beyond the terminal spine. The telson of P. m e la nd i being armed with 10 setae, whereas in P. j a s i the telson is densely set with 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. melandi).

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 (lateral setae are present in these three species). The new species can be distinguished from P. a n t a rc t i c u m by the ocular plate serration (quite conspicuous serration in P. melandi versus finely serrated in P. a n t a rc t i c u m), by the apex of the telson (armed with five pairs of setae versus three or four pairs in P. antarcticum) and the shape of mandibles, maxilla and male pleopods. The new species can be distinguished from P. bellingshausensis by the serration of the ocular plates (fewer number of serrations in P. melandi), the number of setae arming the inner margin of the antennular peduncle (without setae in P. bellingshausensis versus three setae on second and six setae on third article in P. melandi), the outer margin setae of the first thoracopod endopod (armed with a row of small setae in P. bellingshausensis, absent in P. melandi) and the telson armature.