Dubinectes, 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 : 4-12

Dubinectes gen. nov

Type species: D. acutitelson ( Menzies, 1962) .

Species included: D. acutitelson ( Menzies, 1962) , D. nodosus ( Menzies, 1962) , D. acutirostrum sp. nov. and D. intermedius sp. nov.

Etymology

From Latin dubius, meaning doubt and Greek nectes, meaning swimmer, because these animals, as it might be assumed, are not only adapt for swimming, but also for digging. The strong calcified integument, the large, heavy and deep head with the stout rostrum, with mouthparts very tightly closed by maxillipeds, and posterioventral projection related with the peculiar shape of uropods seem to be adapted for digging in soft sediments. Gender masculine.

Diagnosis

Pleotelson posterior margin surrounded with rim: additional structure, running perpendicular to the margin, projecting ventrally and raising over dorsal surface. Uropod protopod bent at midlength, both margins angled: concave lateral corner and projected medial corner, bearing long setae. Body with strong calcified integument, deepest at the head. Head not narrower than ambulosome; rostrum long and robust, larger than article 1 of antenna 1, with 2 robust distal setae. Distomedial lobe of article 1 of antenna 1 reduced, shorter than distolateral projection. Pereonites 1–4 subequal in width, loosely packed, pereonite 1 longest, pereonite 4 nearly a third the length of pereonite 1, pereonite 7 not longer than pereonite 6. Mandible with longitudinal outer keel, high sharp ridge between short spine row and broad molar; condyle longer than molar. Pereopods 1–4 subequal in length. Male pleopod 1 distolateral lobes produced, longer than tiny distomedial lobes. Male pleopod 2 protopod distal margin truncated; exopod inserting close to distal margin and emerging posteriorly; endopod basal article twice as broad as stylet; stylet approximately two times longer than protopod.

Description

Body length approximately 3 times width, with strong calcified integument, deepest at head. Rostrum broad, stout, exceeding article 1 of antenna 1, terminating with 2 robust setae, tip overhanging high frons; lateral margin of head with ledge; in dorsal view forming a step with a stout seta; in lateral view lateral spine blunt. Head and ambulosome of the equal width, pereonites shortening from 1 to 4; coxae of pereopod 4 broadest in lateral view. Natasome with dorsal articulations; venter with medial keel; pereonite 5 longest and broadest, pereonite 7 shorter or subequal to pereonite 6; anterolateral corners of pereonites 6, 7 and pleotelson acute and bent dorsally. Pleotelson with pair of dorsal tubercles on anterior part; posterior margin surrounded by outer rim with shorter dorsal part and longer ventral section, which may be pronounced into ventral projection; preanal ridge pronounced.

Antenna 1 nearly one third of body length, inserted deeply into the antennal socket, article 1 distomedial lobe reduced, shorter than distolateral acute projection, article 3 length nearly twice the length of article 2. Antenna 2 article 1 triangular; article 2 laterally shorter than article 1, scale on article 3 nearly half the length of article 4. Mandibular body with longitudinal outer keel, molar process broadening distally, ventral margin of triturative surface with row of denticles and few setulose setae; spine row with few spines, high acute ridge between spine row and molar, condyle 0.3 times body length, longer than molar; palp 0.9 times body length, article 2 broadened at midlength. Maxilla 1 lateral endite nearly 1.5 times as wide as mesial endite, with 12 distal stout setae, mesial endite distally with tuft of small slender setae and 2 long setulate setae. Maxilla 2 middle endite shortest, mesial and lateral endites of the same length, mesial endite with dense tuft of distal setae, some of them comb­like; lateral and mesial endites each with 2 long and 2 shorter distal setae. Maxilliped epipod subequal to basis, sub­triangular, with lateral angled extension, tip pointed.

Pereopods 1 – 4 similar in length, becoming more slender from 1 to 4; bases of pereopods 1 – 4 subequal in length, basis 1 broadest; carpi of pereopods 2 and 3 and propodus of pereopod 2 with stout, flagellate ventral setae; propodi of pereopods 2 – 4 with tuft of distal long simple setae. Pereopods 5 – 7 strong, of similar shape, pereopod 5 longest, basis 5 about quarter basis 4 length, bases becoming longer, ischii shorter, carpi and propodi decreasing in size from pereopods 5 to 7, dorsal margin of carpi more convex than ventral margin, propodi shorter and about half carpi width, ventral margin more convex than dorsal margin; dactyli almost as long as propodi width, with stout acute dorsal claw and ventral slender seta.

Male pleopod 1 length nearly 2.5 times width, with greatest volume ventrally; distal margin of sinuate shape: lateral lobes produced posteriorly, with acute distodorsal projections, medial lobes somewhat reduced, narrow and shorter than lateral lobes. Male pleopod 2 protopod length 0.7 times pleopod 1 length, distal margin truncated, exopod very prominent behind protopod distal margin, and with projected distal section; endopod basal article swollen, stylet slender, about twice as long as protopod, sperm duct opening after basal fourth of stylet.

Uropod protopod bent at midlength, with both margins angled: concave lateral corner and projected medial corner, bearing long setae, endopod longer than protopod, exopod less than a half endopod length.

Remarks

The key characters for the new genus are the distinctive shape of the posterior margin of the pleotelson, related to the unique shape of the uropod protopod. Many species of Eurycope , and especially some species of Munneurycope Stephensen, 1912 , have the posterior part of the pleotelson to some extent bent downwards. Thus the line of the posterolateral margin angles downward in lateral view but in all these cases this line is just a clear, sharp border between the dorsal surface and ventral side of the pleotelson ( Fig. 2 ). The shape of the pleotelson posterior margin in the new genus is characteristic and unique within Eurycopinae . The pleotelson edge has an additional structure, which appears to be a rim with an outer ring running perpendicularly to the edge. This has a short dorsal section rising over the dorsal surface and a protruding ventral section. The shape of the bent uropod protopod, divided into two parts by a middle angle, is also unusual among Munnopsidae . In some Eurycope species , (e.g. species of the E. complanata complex, some species of the E. longiflagrata complex and in some species of Coperonus ) the short and broad protopod also has a medial extension. However, but the protopod has a different shape, resembling a shoe, with a short straight lateral side and long distal and medial sides ( Fig. 4 ).

The new genus with the general Eurycope habitus has an unusual enlarged, deep head, which is particularly distinct in lateral view (compare in Figs 1 and 2 ). The combination of the long, stout rostrum, and reduction of the distomedial lobe of article 1 of antenna 1 characterises four other eurycopine genera, but not Eurycope ( Fig. 1 ). E. producta , species of the E. dahli complex, Disconectes , Tytthocope , and Belonectes possess a long and broad rostrum, but without 2 terminal stout setae. Most species of these four genera have a rostrum with cephalic keels ( Wilson & Hessler 1980: 245), some species have denticles on the rostral margins and the tips of such rostrum may appear to bear terminal setae in dorsal view. Some species of Eurycope and Disconectes have small, slender distal setae on the rostrum, but this is a different armament. A similar armament of a rostral tip occurs in species of the E. longiflagrata complex and E. tumidicarpus Schmid, Brenke and Wägele, 2002 , but the few terminal setae are slender, not as robust and obvious, as in the new genus ( Fig. 1 ).

The mandibles of Dubinectes gen. nov. also have some unusual features for Eurycopinae : i.e. the longitudinal keel on the outer side of the mandibular body and the high acute ridge between the spine row and the broad molar. The condyle is also longer than the molar, while it is typically shorter in all Eurycopinae , except Baeonectes ( Fig. 3 ). The expansion of the palp article 2 at midlength has not previously been recorded for species of Eurycopinae .

The male pleopods 1 and 2 of the new genus possess a unique shape. The pleopod 1 distomedial lobes are narrow and shorter than the distolateral lobes. In comparison, all Eurycopinae , except the E. longiflagrata complex, are characterised by the broad and rather protruded distomedial lobes ( Fig. 4 ). The male pleopod 2 of the new genus has a protopod with a truncated distal margin, so the exopod emerges posteriorly and terminally from it. Most of the munnopsid species have a protopod that tapers distally and the exopod emerges from the distal part of the medial margin ( Fig. 4 ). A similar truncated shape of the protopod and the exposure of the exopod have been described in Munnopsidae only for species of the E. longiflagrata complex and for some species of Munneurycope ( Wolff 1962; Svavarsson 1987). The endopod has the swollen basal article and the elongate stylet, which is approximately twice as long as the protopod. This differs from the common shape in the subfamily ( Fig. 4 ) where both articles are of subequal width and the stylet is shorter than the protopod or subequal to it, as in E. cornuta . Again, the only eurycopine group with a similarly shaped endopod is the E. longiflagrata complex. In addition to the genital characters, both groups possess features which distinguish them from most of the other Eurycope species. These include: the short pereonite 4, which is only a third of the pereonite 1 length ( Figs 1 and 2 ), in contrast to the typical state (pereonites 1 – 4 of similar length); the body is deepest at the head – pereonite 1 area instead of at pereonite 5 or 6 as usually found in Eurycope ( Figs 1 and 2 ).

Despite these similarities the new genus and the E. longiflagrata complex cannot be grouped into one genus because they differ in the structure of the posterior margin of the pleotelson, the protopod of the uropod and in other characters. For example: 1. the new genus possesses a thick, long rostrum, overhanging the frons, while the rostrum is short and narrow in the E. longiflagrata complex. 2. The new genus has a relatively shorter natasome (about half of the body length contrary to 0.7 in the E. longiflagrata complex), and the longest natasomite is the pereonite 5 (in E. longiflagrata complex, as in all Eurycope species , it is the pereonite 7). 3. Dubinectes gen. nov. also differs in the presence of a pair of tubercles on the anterior half of the dorsal surface of the pleotelson. This structure was also found in E. glabra Kensley, 1978 , another species excluded from Eurycope ( Wilson & Hessler 1981) . 4. The mandibles of Dubinectes gen. nov. have a high acute ridge between the spine row and the molar and the condyle longer than the molar, contrary to the E. longiflagrata complex, which has the usual subfamily character of an approximate right angle between the spine row and the molar, and the short condyle. 5. The distomedial lobes of the male pleopod 1 are present, not completely reduced, as in the E. longiflagrata complex. 6. The stylet of the male pleopod 2 is about twice as long as the protopod (3 to 4 times in the E. longiflagrata complex). Concerning the E. longiflagrata complex Wilson (1983 b) wrote, “its possession of unusual characters opens the possibility of the creation of a new genus, or the division of Eurycope into subgenera”. It is very probable that the E. longiflagrata complex also represents a new genus. However, we do not have species of this complex in the ANDEEP material and, as the revision of Eurycope is not the purpose of this paper, we leave the erection of a new genus for a future investigation. Distribution and comparison of the main characters among the genera of Eurycopinae is presented in Table 1.

Distribution

The species of the genus Dubinectes gen. nov. have been found in the south­eastern Atlantic and in the Weddell Sea, Southern Ocean. The depth ranges between 1121 and 4960 m.

Figures

FIGURE 1. Representatives of the subfamily Eurycopinae, dorsal view of body (two upper rows) and right antenna 1 (two lower rows, in the same sequence): a, Eurycope cornuta Sars, 1864; b, Eurycope complanata complex Wilson, 1982; c, Eurycope dahli complex Svavarsson, 1987; d, Eurycope longiflagrata complex Wilson, 1983; e, Dubinectes gen. nov.; f, Disconectes Wilson & Hessler, 1981; g, Baeonectes Wilson, 1982; h, Tytthocope Wilson & Hessler, 1981; i, Belonectes Wilson & Hessler, 1981.

FIGURE 2. Representatives of the subfamily Eurycopinae, lateral view of body (two upper rows) and lateral view of pleotelson (two lower rows, in the same sequence): a, Eurycope cornuta Sars, 1864; b, Eurycope complanata complex Wilson, 1982; c, Eurycope dahli complex Svavarsson, 1987; d, Eurycope longiflagrata complex Wilson, 1983; e, Dubinectes gen. nov.; f, Disconectes Wilson & Hessler, 1981; g, Baeonectes Wilson, 1982; h, Tytthocope Wilson & Hessler, 1981; i, Belonectes Wilson & Hessler, 1981.

FIGURE 3. Representatives of the subfamily Eurycopinae, mandibles (two upper rows) and maxillipeds (two lower rows, in the same sequence): a, Eurycope cornuta Sars, 1864; b, Eurycope complanata complex Wilson, 1982b; c, Eurycope dahli complex Svavarsson, 1987; d, Eurycope longiflagrata complex Wilson, 1983; e, Dubinectes gen. nov.; f, Disconectes Wilson & Hessler, 1981; g, Baeonectes Wilson, 1982; h, Tytthocope Wilson & Hessler, 1981; i, Belonectes Wilson & Hessler, 1981

FIGURE 4. Representatives of the subfamily Eurycopinae, distal margin of male pleopod 1 (two upper rows), male pleopod 2 (two middle rows) and uropod (two lower rows, in the same sequence): a, Eurycope cornuta Sars, 1864; b, Eurycope complanata complex Wilson, 1982; c, Eurycope dahli complex Svavarsson, 1987; d, Eurycope longiflagrata complex Wilson, 1983; e, Dubinectes gen. nov.; f, Disconectes Wilson & Hessler, 1981; g, Baeonectes Wilson, 1982; h, Tytthocope Wilson & Hessler, 1981; i, Belonectes Wilson & Hessler, 1981.