Dubinectes infirmus, Malyutina, Marina & Brandt, Angelika, 2011

Malyutina, Marina & Brandt, Angelika, 2011, Dubinectes infirmus, a new species of deep-water Munnopsidae (Crustacea, Isopoda, Asellota) from the Argentine Basin, South Atlantic Ocean, ZooKeys 144, pp. 1-19 : 4-10

Dubinectes infirmus sp. n. Figs 2-9

Material examined.

Argentine Basin, RV Meteor.

Holotype:(ZMH 42969), male (3.0 mm), DIVA 3 Station 534 16.07.2009 36°00.61'S, 49°01.55'W, 4586-4605 m.

Paratypes:(ZMH 42970) damaged male used for dissection of mouthparts and pleopods, female 3.0 mm, male 3.1 mm, female 3.8 mm, mancas 2.5 and 2.1 mm, the same sample from the same locality; (ZMH 42971) 1 male, 2 females and 2 mancas (1.8-3.4 mm), Station 532, 15.07.2009 35°59.24'S, 49°00.86'W, 4605-4607 m.

Diagnosis.

Rostrum of head with rounded apex; antennula article 3 subequal in length to article 2; anterolateral margins of pereonites 6, 7, pleotelson and posterior rim of pleotelson weakly pronounced, not raised dorsally; pleopod 1 distomedial lobes of the same size as distolateral lobes; endopod stylet of male pleopod 2 subequal in length to protopod. Uropod exopod more than half of endopod length.

Description.

Holotype male: body (Fig. 2) length 2.8 times width of pereonite 5, body height 0.25 of body length. Head length 0.55 times width; length behind antennula insertion 1.1 antennula article 1 length; rostrum as long as proximal part of head, distally convex, with 4 setae; clypeus 1.6 as wide and 0.5 as long as labrum. Pereonite 1 almost as wide as head, length 0.8 length of head behind antennula insertion; pereonites 1-4 subequal in width, shortening from 1-4, pereonite 4length about half of pereonite 1 length; anterolateral margins of pereonites 1-4 and anterior projections of coxae acute, anterolateral angles of pereonite 4 slightly projected, terminating with seta. Natasome length 0.5 body length, width 1.3 width of head; pereonite 5 longest, lateral length 0.7 of lateral length of pereonites 6 and 7 together; pereonite 7 shortest, 0.8 times length of pereonite 5. Pleotelson length 0.9 width, slightly longer than head, 0.25 body length, preanal ventral ridge weakly projected, rounded terminally; anterolateral corners of pereonites 6, 7 and pleotelson acute, weakly projected, terminating with seta. Proportions of habitus and body parts in females and juveniles (Figs 3, 8) are equal to those of the holotype.

Antenna 1 of male (Fig. 4) article 1 1.05 times width, setation: 1 dorsal and 1 distolateral broom seta and 1 simple seta, 1 stout unequally bifid and 2 broom setae distomedially; article 2 0.6 times length and 0.4 width of article 1, with 1 simple and 2 distal broom setae; article 3 0.7 length of article 2 with 2 simple setae, article 4 0.3 times length of article 3, article 5 twice as long as article 4, following 11 flagellar articles subequal in length to article 4, some of the distal articles with an aesthetasc. Antenna 1 of female (Fig. 9) article 2 length 0.65 times length of article 1, article 3 slightly longer (1.1) than article 1, article 4 length 0.35 times article 3 with broom seta and aesthetasc distally; flagellum of 5 articles, last one with 1 aesthetasc and 5 setae.

Antenna 2 of female(Fig. 8) articles 1-4 subequal in size, length together 0.6 times body length, scale on article 3 nearly half the length of article 4. Article 5 almost as wide and 2.1 times as long as articles 1-4 together, with 3 stout medial setae and 2 small simple distolateral setae, article 6 narrower and 1.1 times as long as article 5, with simple setae along article. Flagellum broken off, articles subequal in length to article 1.

Mandibles (Fig. 4) longitudinal outer keel of body weakly pronounced, incisor process with 2 acute and 1 weak cusps; lacinia mobilis of left mandible triangular with many denticles, 0.8 times length of incisor process; spine row with 5 and 6 spines on left and right mandibles respectively; molar process 0.5 times as long and as broad as incisor process on proximal part, ventral margin of triturative surface with a few denticles and 3 setulose setae; ridge between spine row and molar with 1 pick; condyle 0.3 times body length, longer than molar; palp 0.9 times body length; article 1 with 2 distal setae, article 2 broadened at midlength, length 2.2 times article 1 length, with 3 stout distal setae and small marginal setae, article 3 0.75 of length and 1.15 of width of article 2, with 3 long simple distal setae and long comb-like marginal setae.

Hypopharynx (Fig. 5) outer lobes 3.7 times as wide as inner lobes with dense distal fine setae and four lateral setae each.

Maxilla 1 (Fig. 5) lateral endite 1.35 times as wide as mesial endite, with 12 distal stout serrated setae, mesial endite distally with tuft of small slender setae and 1 long setulate seta.

Maxilla 2 (Fig. 5) middle endite shortest, lateral endite longest, mesial endite with dense tuft of distal setae, longest one setulate; lateral and mesial endites each with 2 long and 2 shorter distal setae.

Maxilliped (Figs 5, 9) basis 2.7 times width, endite with 3 coupling hooks (2 in immature female), distal margin with 4-5 large fan setae and numerous simple slender setae; palp article 2 margins almost straight, lateral margin 1.3 times longer than medial margin; article 3 medial margin slightly convex, with low denticles and 5 setulose setae, 1.2 times longer than medial margin of article 2; article 4 2 times longer than articles 3 laterally, medial lobe almost not produced, with 4 distal setae, article 5 0.9 of article 3 laterally, with 7 distal setae. Epipod subequal in length to basis length 1.6 times width, lateral extension rounded, almost as broad as distal angle.

Pereopods 1-4 bases subequal in size. Pereopod 1 (Fig. 9) 0.3 times body length, length ratios of ischium-propodus to basis: 0.5, 0.3, 0.9, 0.7, 0.2; basis with small setae: 3 ventral and 1 dorsal; merus with 1 small ventral seta; carpus with 4 small ventral and 3 dorsal setae; propodus only slightly narrower than carpus, with 3 ventral and 5 dorsal setae; dactylus with elongate claw, 3 slender setae proximally claw.

Pereopod 3 (Fig. 6) length ratios of ischium-propodus to basis: 0.5, 0.3, 1.0, 0.9, 0.75; basis with 1 plumose dorsal seta, ischium with 1 distoventral seta, merus with 1 distodorsal seta, carpus with 7 short unequally bifid ventral setae, 1 broom distodorsal seta and 3 small dorsal setae, propodus 0.7 of carpus width, with 5 unequally bifid ventral setae longer than these on carpus, 1 distodorsal seta and 5 small dorsal setae, dactylus with elongated claw. Pereopod 4 (Fig. 6) slightly shorter and more slender than pereopod 3, propodus longer and dactylus shorter than these in pereopod 3; length ratios of ischium-propodus to basis: 0.5, 0.3, 1.05, 1.05, 0.6; basis with 4 plumose dorsal and 9 simple small ventral setae; ischium without setae, merus with 3 distal set ae; carpus with 2 short unequally bifid ventral setae, 1 whip and 3 stout unequally bifid distodorsal setae and 6 small dorsal setae; propodus 0.6 of carpus width, with 1 ventral and 2 dorsal small simple setae, and1 broom seta, 2 whip and 2 small setae distally.

Pereopods 5-7 (Figs 6, 9) of same shape, decreasing from 5 to 7, with stout basis- ischium, bases lengths about half of bases of pereopods 1-4; plumose marginal setae on carpi elongate, longest setae length about 0.7 of carpus width; plumose marginal setae on propodi stout, about half length of marginal setae on carpi; both articles with the same set of short setae distodorsally: 2 stout unequally bifid, 1 broom and 1 whip seta; dactyli with tiny claw and 2 setae distoventrally. Pereopod 5 length 0.65 pereopod 3 length; length ratios of ischium-carpus to basis: 1.3, 0.7, 1.6, 1.2, 0.6; basis with 5 dorsal broom setae; ischium with 5 dorsal plumose setae; merus with 3 small ventral simple setae; carpus length 1.3 times width, with 19 dorsal and 10 ventral plumose elongate setae; propodus 1.3 times width, with 12 dorsal and 9 ventral plumose stout setae; dactylus width 0.2 propodus width. Pereopod 6 length 0.9 pereopod 5 length; length ratios of ischium-dactylus to basis: 1.05, 0. 5, 1.5, 1.0, 0.6; basis with 1 dorsal and 3 ventral setae; ischium with 5 plumose dorsal and 3 simple ventral setae; merus with 1 ventral seta; carpus length 1.3 times width, with 17 dorsal and 9 ventral plumose elongate setae; propodus 1.7 times width, with 11 dorsal and 9 ventral stout plumose setae; dactylus width 0.2 propodus width. Pereopod 7 length 0.7 pereopod 5 length, length ratio of ischium-dactylus to basis: 1.05, 0.5, 1.3, 1.0, 0.6; basis with 1 plumose ventral seta and 1 whip dorsal seta; ischium with 4 plumose dorsal and 2 ventral setae; merus with 2 small ventral setae; carpus 1.05 times width, with 16 dorsal and 8 ventral elongate plumose setae; propodus 1.6 times width, with 10 dorsal and 5 ventral stout plumose setae; dactylus width 0.3 propodus width.

Pleopods (Fig. 7): pleopod 1 of male 2.25 times width, distal margin: lateral lobes acute slightly projected laterally, with 5 distal small setae each; medial lobes rounded, almost as wide as and slightly longer than lateral lobes, with 2 small distal setae each. Pleopod 2 of male protopod length 1.7 times width, 0.75 as long and as wide as pleopod 1, with 2 lateral submarginal setae, stylet of endopod length 0.9 protopod length, exopod prominent and visible behind distal truncated margin of protopod, distolateral hook rounded, with tuft of fine setae. Pleopod 3 endopod 1.3 times width, 3 distal plumose setae only slightly shorter than endopod; exopod basal width 0.4 endopod width, length 1.1 endopod length, reaching beyond endopod distal margin, with dense row of hair-like lateral setae and 1 distal simple seta, length 0.25 exopod length. Pleopod 4 endopod length 1.3 times width, exopod 0.4 of width and 0.9 of length of endopod, with dense row of lateral slender setae, distal seta plumose, length 1.4 exopod length. Pleopod 5 endopod length 1.4 times width.

Pleopod 2of female as long as wide, with medial keel, 2 long simple setae proximolaterally and 10 small simple setae on posterior margin (Fig. 3).

Uropod (Fig. 7) length 0.3 times pleotelson length; protopod as long as wide, with 5 long whip setae on medial projection and several distal setae, endopod 0.33 times as wide and slightly longer than protopod, with 1 lateral and one distal broom and 6 whip setae; exopod length 0.7 times endopod length, with 4 setae distally.

Distribution.

Southwest Atlantic: northern Argentine Basin at depths between 4586-4605 m.

Etymology.

The epithet infirmus (Latin) refers to the state of the generic characters of the species, which are less obvious than in other species.

Remarks.

Dubinectes infirmus sp. n. differs from the four other species of the genus by weakly pronounced generic characters: a rim, surrounding the pleotelson posterior margin is narrow, not raising over the dorsal surface; lateral margins of the head are without an obvious ledge, anterolateral angles of pereonites 5-7 and pleotelson not produced dorsally. Article 3 of male antennula in the new species is shorter than article 2, in females and juveniles it is slightly longer than article 2 in contrast to other species which have article 3 nearly twice as long as article 2; pleopod 1 distolateral lobes are subequal in size to the distomedial lobes (in other species they are broader and longer); the endopod stylet of male pleopod 2 is subequal in length to the protopod (0.9) in contrast to state in other species which is approximately two times the length of the protopod; both endopod and exopod of the uropod are rather stout, shorter than in other species, the exopod is 0.7 times the endopod length (0.35 - 0.5 in other known species). The new species is the most similar to Dubinectes nodosus in body shape and size of the rostrum, but the new species has a less calcified cuticle, a rounded tip of the rostrum, a narrow posterior rim of the pleotelson, not raising dorsally, shorter article 3 of antennula and another configuration of distal margin of pleopod 1 than in Dubinectes nodosus .