Microcope, Malyutina, Marina V., 2008

Malyutina, Marina V., 2008, Microcope gen. nov. — a new deep-sea genus of Munnopsidae (Crustacea, Isopoda, Asellota), with description of two new species from the Southern Hemisphere, Zootaxa 1866, pp. 555-574 : 556-558

Microcope gen. nov.

Type species: M. denticulata sp. nov.

Species included: M. denticulata sp. nov., M. levissima sp. nov. and M. ovata ( Birstein, 1970) .

Etymology: The name refers to the minute size in combination with the former generic name of the first species of the genus.

Diagnosis. Head short, not visible, hidden under anterior transparent flange of pereonite 1; rostrum absent, antennulae inserted closely to each other; frons high, triangular; mouthfield narrow, protruded ventrally. Pereonites 1 and 2 longer than pereonites 3 and 4. Natasome larger than ambulosome, with continuous oval configuration, pereonites 5–7 fused dorsomedially, dorsolateral articulations short, about half of natasome height, pereonite 5 longer laterally than combined pereonites 6 and 7, pereonite 7 shortest; pleotelson broader than long, subtriangular, uropods inserted ventrally, anus separated from pleopodal cavity by flattened lengthy space, not covered by operculum. Antennula article 1 about as long as wide, with narrow triangular distomedial lobe, article 3 subequal in length to article 2. Mandible molar process cylindrical, elongate, longer than condyle; palp strong, subequal or longer than mandibular body. Maxilliped epipod about as long as basis, elongate triangular. Pereopods 1–4 basis subequal in length, pereopods 2–4 with conspicuous difference between bulky basis–ischium part and slender carpus–dactylus part. Pereopods 5–7 similar in shape and size, carpi and propodi moderately expanded (propodi smaller), dactyli slender, almost as long as propodi. Female pleopod 2 ovoid, slightly bulging proximomedially, flattened distally, with dense row of long marginal setae, distal margin truncate. Male pleopod I distolateral lobes pointed, shorter and narrower than rounded distomedial lobes; pleopod 2 protopod slender, length about 4 times width, stylet length 0.8 protopod length, exopod stout. Pleopod 3 endopod distal half almost twice as broad as narrow basal half, distal plumose setae longer than endopod; exopod about as wide and 1.5 as long as endopod, distal seta tiny. Uropod protopod with medial extension, rami inserted in midlength of lateral margin, endopod distinctly longer and broader than exopod.

Additional description. Body highest at ambulosome, head length about 0.2 width, frontal margin with short angled medial prominences, without rostrum, frons triangular, higher than dorsal part of head and clypeus and labrum together, acute anterior, with small medial convexity; clypeus 1.8 as wide and as long as labrum. Pereonites 1–4 tightly articulated, gradually broadening from 1 to 4, 1 and 2 distinctly longer than 3 and 4; anterior flanges overhanging posterior section of preceding segment; pereonites 2–4 lateral margins sinuate, anterolateral projections tipped with stout seta; coxae with anterior lobe, emerging behind the anterolateral projections of pereonite. Pereonites 5–7 dorsomedially fused without sutures, ventrally with sutures, ventrolateral margins rounded, dorsolateral articulations extended posteriorly. Pleonite 1 narrow stripe, pleotelson with ventrolateral row of dense setae, posterior margin rounded.

Antennula article 1 distomedial triangular lobe truncate distally. Mandibular spine row with few spines, molar process more than twice as long as condyle, cylindrical, truncated distally, ventral margin of triturative surface with row of spines and stiff setae; palp strong, not shorter than body, article 3 relatively large, 0.4 as long as longest article 2. Maxilliped epipod elongated, subequal to basis, length about 3 times width, proximal third of lateral margin rounded, slightly protruding; articles 2 and 3 of maxilliped palp expanded, article 3 medial margin dentate, medial lobe of article 4 convergent, with broad basis.

Pereopods 1–4: pereopod 1 shortest, pereopods 3 and 4 longest, about 1.6 as long as pereopod 1; basis 1 most slender, basis 4 most stout; ischium and merus of pereopods 3 and 4 longer and stouter than those of pereopod 2, of the same width, carpi of pereopods 2–4 of the same width, increasing in length from 2 to 4; propodi increasing in length and decreasing in width from 2 to 4. Pereopods 5–7: pereopod 6 longest, pereopod 7 shortest; pereopod 5 with shortest and stoutest basis-ischium part and narrowest carpus, pereopod 7 with most elongate basis–ischium, relatively broad and short carpus and long propodus; propodi inserted from distoventral side of carpi more ventrally than on usual swimming paddle-like pereopods; carpi and propodi elongate oval, with 3 different types of setae: usual plumose setae on proximal half of articles, stout plumose setae with short setulae more distally and spine-like stout unequal bifid setae on distal third of articles.

Female operculum ovoid, proximomedial part slightly bulging, distal half flattened, with dense row of plumose whip marginal setae, distal margin truncate, with additional submarginal setae. Male pleopods 1 and 2 covering pleopodal cavity tightly. Pleopod 1 with parallel sides, distal part with lateral setae; distolateral lobes pointed and curving slight toward midline, slightly shorter and clearly narrower than rounded distomedial lobes. Pleopod 2 protopod elongate, lateral margin with long plumose setae; endopod and exopod inserting from distal third of protopod; stylet approximately 0.8 as long as protopod length. Pleopod 3 endopod with 3 plumose distal setae, two of them inserting closely to each other laterally, third seta inserted at distance medially; exopod semicircular, about as wide and 1.5 longer than endopod, with thin lateral setae and tiny distal seta. Pleopod 4 exopod equal in length and half as wide as endopod, with long plumose seta, which is equal in length to plumose setae on pleopod 3. Uropod protopod with row of ventral long setae along lateral margin, endopod slightly shorter than protopod, and longer than exopod.

Remarks. In the dorsal view of the holotype of Eurycope ovata Birstein (1970: 326, Fig 14) drew a head in front of pereonite 1, which is most likely not a head, but an anterior flange of pereonite 1, as can be seen in both of the new species described here. Birstein also drew a complete suture between pereonites 6 and 7. Yet, in all studied specimens of the new species this line coincides with the border of the pereopod 7 muscle tissue, which is visible through the integument. At first glance, E. ovata illustrated by Birstein resembles small lipomerinas, e.g.. some species of Coperonus Wilson, 1989 or Lionectes Wilson, 1989 , due to its small oval body (1–2 mm), lack of rostrum and reduced pereonite 7. In contrast to the Lipomerinae , though, the new genus has fused pereonites 5 and 6, a smaller and flattened female operculum, which does not cover the anus, and a different shape and position of the uropods; pereopod 7 is not reduced and similar to pereopods 5 and 6.

Microcope gen. nov. superficially resembles some Eurycopinae , especially some species of Disconectes Wilson and Hessler, 1981 and Baeonectes Wilson, 1982 , in possessing a broad body with enlarged rounded natasome, fused natasomal pereonites and similar mouthparts. Yet, it cannot be assigned to the Eurycopinae due to the lack of rostrum, different shape and size of opercular pleopods, and modified uropods.

The new genus resembles Betamorphinae in having similar shape and position of the basal articles of antennulae, narrow mouthfield that is protruded ventrally, similar morphology of pereopods 1–4, the extended anterior flange of pereonites 1 and 2, sinuate lateral margin of pereonites 1–4 with coxal lobes emerging behind anterolateral projections of pereonites, the protopod of the uropod with a medial extension and the arrangement of the ventral side of pleotelson. Microcope gen. nov. differs from existing genera of Betamorphinae , Betamorpha Hessler and Thistle, 1975 and Amuletta Wilson and Thistle, 1985 , by dorsomedially fused natasomal pereonites (the Betamorphinae have full dorsal articulations); flattened female pleopod 2 without medial keel, which is typical for Betamorphinae ; different arrangement of pleopods 3 and 4, and elongated oval carpi of pereopods 5–7, which are broad and triangular in Betamorphinae .

Some characters of the new genus are also common for species of Syneurycopinae , e.g. Bellibos Haugsness and Hessler, 1979 , such as fused pereonites 5–7, shape and position of the operculum in both sexes, which occupies about half of the ventral surface of pleotelson, broad and flattened bridge between the pleopodal cavity and anal operculum with posterior row of long setae. The Syneurycopinae is distinguished by many autapomorphies such as narrow body, reduced natasome and nearly tubular basal articles of antennulae, and cannot be considered as a close relative of Microcope gen. nov.

Thus in spite of the above mentioned similarities, Microcope gen. nov. cannot be placed into any existing subfamily and remains incertae sedis. Distribution of characters in some munnopsid genera is presented in Table 1.

Distribution. The species of the genus Microcope gen. nov. were found in the Kuril-Kamchatka Trench (northwestern Pacific), and in the Southern Hemisphere, i.e. in the south-eastern Atlantic (Cape Basin) and Southern Ocean ( Scotia and Bellingshausen seas, west of the South Shetland Islands). The depth ranged between 2014 and 5054 m.