Dubinectes acutirostrum, Malyutina & Brandt, 2006

Malyutina, Marina & Brandt, Angelika, 2006, A revaluation of the Eurycopinae (Crustacea, Isopoda, Munnopsidae) with a description of Dubinectes gen. nov. from the southern Atlantic deep sea, Zootaxa 1272 (1), pp. 1-44 : 19-27

Dubinectes acutirostrum sp. nov.

( Figs 7–11 )

Material examined

Holotype ( ZMH 41149), male (5.5 mm), ANDEEP II Stn. 137­4, 14 March 2002, 63°44.98’S, 38°47.75.61’W, 4976 m.

Etymology

acutirostrum means provided with acute rostum, referring to the special shape of the rostrum of the species.

Diagnosis

Body stout with thick cuticle, rostrum thick, tapering, equal in length to four basal articles of antenna 2; head lateral ledge rectangular; natasome length approximately egual to anterior part of body, anterolateral margins of pereonites 6, 7 and pleotelson greatly extended anterodorsally; posteroventral process of pleotelson thick, pointed, about half the length of the pleotelson; male pleopod 1 with small lateral ledges on base of distolateral lobes; uropod protopod angled at 90º, medial angle projected, exopod length 0.35 times length of endopod.

Description of holotype

Body ( Fig. 7 ) length 2.9 times length of pereonite 5. Head length 0.7 times width; lateral ledge rectangular; rostrum length 1.4 times length of the rest of the head, tapering; clypeus 1.5 times as broad and 0.3 times length of labrum.

Pereonite 1 slightly wider than head, pereonite 4 length 0.3 times length of pereonite 1; pereonite 7 length 0.8 times length of pereonite 5. Pleotelson length 0.7 times width and equal to length of head medially; posteroventral projection 0.5 times length of pleotelson.

Antenna 1 ( Fig. 8 ) article 1 length 1.2 times width, setation: 3 dorsal broom setae and 2 distomedial simple setae; article 2 length 0.5 times length of article 1, with 2 broom and 2 small simple distal setae; articles 3 subequal to article 1, flagellum of 21 articles, article 4 length 0.1 times length of article 3, with distal broom seta, following 3 articles longer, remaining articles about equal length to article 4, from article 6 each with aesthetasc.

Antenna 2 incomplete ( Fig. 8 ): article 3, dorsal side, almost twice length of article 2, scale length 0.4 times length of article 4, with distal seta; article 4 subequal to article 3.

Mandibles ( Fig. 9 ) pars incisiva with 3 weak cusps (on right mandible central cusp longest); lacinia mobilis of left mandible stout, length 0.9 times length of pars incisiva, with 8 teeth; spine row with 4 and 5 spines on left and right mandibles respectively; ventral margin of molar process triturative surface with 5 setulose setae; palp article 2 length 1.6 times length of article 1, with 3 stout distal setae, article 3 relatively narrow.

Maxilla 1 ( Fig. 8 ) lateral endite 1.4 times width of mesial endite.

Maxilla 2 ( Fig. 9 ) mesial endite with 5 distal comb­like setae.

Maxilliped ( Fig. 8 ) basis length 2.4 times width, endite with 5 coupling hooks, distal margin with 4 large fan setae and numerous simple slender setae; palp article 2 lateral margin length 1.7 times length of medial margin, both margins convex; article 3 medial margin convex, rounded, 1.3 times length of article 2, with short setulose seta, lateral margin length 0.3 times length of article 2; article 4 laterally longer than articles 3 and 5, medial lobe half the length of article 5, with 4 distal setae, article 5 with a tuft of distal setae. Epipod length 1.4 times width and 1.1 times length of basis.

Pereopods ( Fig. 10 ): pereopod 1 length 0.3 times body length, length ratios of ischium­dactylus to basis: 0.5, 0.3, 1.0, 0.7, 0.25; basis with sparse, small ventral setae, 5 proximodorsal broom setae, and 5 distal small, stout setae; ischium with 4 flagellate dorsal setae; carpus straight, with 5 dorsal simple setae and 7 ventral setae (4 simple and 3 stout distally); propodus 0.5 times carpus length, with 4 small dorsal setae; dactylus with 2 dorsal small, simple setae, dorsal claw small, rounded distally.

Pereopod 2 length ratios of ischium­dactylus to basis: 0.6, 0.3, 1.1, 0.9, 0.4; basis with small, simple setae, 1 broom dorsal seta, 2 stout and several simple ventral setae; ischum with 3 stout dorsal setae and 1 simple ventral seta; merus with 7 ventral simple setae and 2 distodorsal stout setae; carpus with 15 ventral stout setae, 3 simple dorsal and 3 distodorsal setae; propodus as wide as carpus, ventral margin with 10 stout and 3 long whip setae, 2 whip setae on side of article and 14 distal whip long setae, dorsal margin with 7 simple setae; dactylus slender, longer than distal setae of propodus, dorsal claw slightly longer than ventral.

Pereopod 3 length ratios of ischium­dactylus to basis: 0.5, 0.4, 1.1, 0.9, 0.4; basis with 3 small ventral and 4 proximodorsal setae: 1 broom and 3 simple; ischium with 2 dorsal and 2 ventral setae; merus with 4 ventral and 2 distodorsal setae; carpus with 7 stout ventral and 5 small dorsal setae; propodus distal half with about 15 whip long setae; dactylus almost equal length of propodus distal setae.

Pereopod 4 length ratios of ischium­dactylus to basis: 0.5, 0.3, 1.3, 1.1, 0.4, basis with 4 dorsal and 2 ventral setae; ischium with 2 ventral and 2 dorsal setae; carpus with 6 ventral and 9 dorsal simple setae; propodus length 0.7 times carpus length, with 2 ventral and 9 dorsal small setae and 15 distal long whip setae; dactylus about equal length of propodus distal long setae.

Pereopod 5 0.7 times length of pereopod 2, length ratios of ischium­dactylus to basis: 2.4, 1.0, 2.4, 2.0, 1.0; basis with 2 dorsal setae, ischium with 14 dorsal setae; merus with 2 ventral setae; carpus length 1.2 times width, propodus length 1.7 times width; dactylus of equal length to propodus distal long setae. Pereopod 6 length ratios of ischium­dactylus to basis: 1.7, 0.7, 1.8, 1.6, 0.9; carpus length 1.2 times width, propodus length 1.7 times width. Pereopod 7 length ratios of ischium­dactylus to basis: 0.9, 0.5, 1.2, 1.0, 0.4; carpus length 1.0 times width, propodus length 1.9 times width.

Pleopods ( Fig. 11 ): pleopod 1 length 2.1 times basal width, distal third of ventral surface with 2 rows of small setae; distal margin: lateral lobes each with 5–7 distal setae, medial lobes slender, about one third width and equal in length to lateral lobes, with 3 distal setae each. Pleopod 2 protopod length 1.5 times width; with 1 marginal and 3 submarginal lateral setae, stylet of endopod 1.6 times protopod length. Pleopod 3 endopod 1.5 times width, exopod 1.2 times endopod length, basal article 0.4 times endopod width, distal article equivalent to 0.6 times and 0.3 times apical length and width respectively, with 1 distal plumose seta. Pleopod 4 endopod slightly larger than pleopod 3, 1.4 times width, exopod 0.4 times width and 0.7 times length of endopod. Pleopod 5 1.3 times width.

Uropod ( Fig. 11 ) 0.4 times pleotelson length. Protopod proximal part subequal in length, but narrower than distal part, medial projection with 7 long whip setae; endopod about half width and almost equal length of protopod, with 1 medial broom seta and 8 distal setae (6 broom and 2 simple); exopod 0.35 times length and 0.5 times width of endopod, with 5 distal setae.

Remarks

The pointed rostrum of the new species easily distinguishes it from D. acutitelson , where all observed specimens have a distal notch to the rostrum. In addition, the two species can be differentiated by: 1. the anterolateral head margins of D. acutirostrum sp. nov. in a dorsal view has a rectangular acute ledge, ending with a stout seta (the head margin of D. acutitelson has a smooth ledge). 2. Pleopod 1 of the new species has a small lateral ledge on the base of the distolateral lobes (the lateral margins are smooth in D. acutitelson ). 3. The exopod of the uropod is relatively shorter in the new species: 0.35 times as long as endopod in comparison to 0.42 in D. acutitelson .

Distribution Known only from the type locality.

Figures

FIGURE 7. Dubinectes acutirostrum sp. nov. Male, holotype, ZMH 41149, a, body dorsal view; b, body lateral views; c, natasome, ventral view; d, pleotelson, terminal view; e, pleotelson, lateral view; f, head, frontal view; g, head, lateral view.

FIGURE 8. Dubinectes acutirostrum sp. nov. Male, holotype, ZMH 41149, antennae, maxilla 1 and maxilliped.

FIGURE 9. Dubinectes acutirostrum sp. nov. Male, holotype, ZMH 41149, mandibles and maxilla 2.

FIGURE 10. Dubinectes acutirostrum sp. nov. Male, holotype, ZMH 41149, pereopods 1–7.

FIGURE 11. Dubinectes acutirostrum sp. nov. Male, holotype, ZMH 41149, pleopods and uropod.