Elocomosta Hansen, 1989

Lin, Renchao, Jia, Fenglong & Fikacek, Martin, 2016, A review of Elocomosta Hansen with a description of a new species with reduced eyes from China (Coleoptera, Hydrophilidae, Sphaeridiinae), ZooKeys 607, pp. 81-92 : 83-85

Taxon classification Animalia Coleoptera Hydrophilidae

Elocomosta Hansen, 1989

Elocomosta Hansen, 1989: 254.

Type species.

Elocomosta nigra Hansen, 1989 (by original designation).

Diagnosis.

The genus may be easily diagnosed from other coelostomatine genera by the combination of the following characters: antenna with thin, loosely segmented club, maxillary palpomere 2 without apparent distal widening, elytron with ten series of punctures (usually not very apparent among interval punctures) but without sutural stria, prosternum rather long in front of procoxae, mesoventrite with subpentagonal to circular plate with marginal bead, without anepisternal sutures and anteromedian pit, metaventrite very short but with long and wide metaventral process abutting posterior margin of mesoventral plate, abdominal ventrite 1 without median carina and abdominal ventrite 5 without apical emargination and/or group of stout setae.

Elocomosta is easy to distinguish from other Oriental coelostomatine genera by the morphology of the mesoventral plate, which is more or less flat and with a bead along the whole margin. In this it differs from Coelostoma Brullé, Coelofletium Orchymont, and Dactylosternum Wollaston, in which the mesoventral plate is keel- or roof-like and generally of the arrow-head-shape morphology. Rhachiostethus Hansen has the mesoventral plate flat, but it is tightly fused to the elevated metaventral keel and lacks the marginal bead. Dactylostethus Orchymont bears the mesoventral plate which is very similar to that of Elocomosta in the shape and in the presence of the marginal bead, but can be easily distinguished from Elocomosta by an extremely short prosternum, elytra without any traces of puncture series, abdominal ventrite 1 with median carina, more compact antennal club and mesoventrite with the anteromedian pit-like depression.

Redescription.

Body widely oval, moderately convex. General coloration of dorsum blackish. Body length 2.3-2.9 mm.

Head situated in a deep anterior emargination of pronotum. Frontoclypeal suture indistinct, only partially developed; preocular portion of frons (between eye and frontoclypeal suture) rather wide. Eyes well developed and strongly constricted laterally, or largely reduced. Anterior margin of clypeus without marginal bead. Labrum weakly sclerotized, largely membranous, narrowly to largely exposed in front of clypeus. Gula very narrow, posterior tentorial pits small and inconspicuous, situated close to each other. Postocular ridges strongly developed, reaching behind cardines. Maxilla with transverse cardo and triangular basistipes, basistipes with sparsely arranged long setae; galea large, partly membranous, with pubescence arranged in series; maxillary palpus with four palpomeres, basal palpomere minute, palpomeres 2-3 only indistinctly widened apically, palpomere 4 cylindrical, palpomere 2 the longest, ca. 1.5 × longer than palpomeres 3 and 4, palpomeres 3-4 subequal in length. Mentum transverse, slightly widening from base anteriad, lateral sides with series of fine setae, anterior margin bisinuate and with transverse subanterior ridge, surface with sparsely arranged long setae; labial palpus with three palpomeres, palpomere 1 minute, palpomere 2 the longest, ca. 1.3 × as long as palpomere 3, bearing subapical fringe of setae, palpomere 2 cylindrical, with subapical setae. Antenna with nine antennomeres; scapus ca. twice as long as pedicellus, antennomere 3 thin and ca. as long as antennomeres 4-5 combined, antennomeres 4-5 slightly widening distally, cupule (antennomere 6) rather wide distally much wider than antennomere 7, antennomeres 7-9 pubescent, forming a very thin loosely segmented club.

Prothorax. Pronotum transverse, deeply excised on anterior margin, strongly widened posterially; anterior and lateral margin with complete marginal bead, posterior margin without marginal bead; posterolateral corners rectangular to acute, posterior margin nearly straight to slightly concave; sublateral portions of pronotum with minute but distinctly developed trichobothria. Prosternum in front of procoxae rather wide, medially flat, without longitudinal ridge, only with a weak transverse impression along anterior margin; prosternal process hidden below procoxae, hence posterior margin of exposed portion of prosternum widely triangular; anterior margin angulate medially, with fine marginal bead, posterior margin finely beaded; concealed portion of prosternal process slightly widened posterior of procoxae. Procoxal cavities contiguous medially, open posteriorly, anterolateral aperture of procoxae very narrowly open to completely closed. Hypomeron with wide lateral bare portion, divided by a very fine line from median pubescent portion; anteromesal portion with a rather indistinct "antennal groove" defined by a weak ridge.

Pterothorax. Scutellar shield rather small, in shape of equilateral triangle. Elytron with ten longitudinal series of punctures but without sutural stria; scutellar stria not developed. Trichobothria minute but present on alternate elytral intervals; epipleuron wide and horizontal throughout, with wide external bare portion. Punctures of elytral intervals with a characteristic structure of several concentric ridges. Mesothorax with strongly elevate mesoventral plate of elongate subpentagonal to circular shape, margins of the plate with distinct wide marginal bead; posterior margin of the plate widely abutting metaventral process; anepisternal sutures reduced, not visible, anteromedian pit absent. Mesanepimeron rather narrow but long, completely closing mesocoxal cavity laterally. Metaventrite transverse, behind mesocoxae very short, shorter than the length of mesoventrite; median portion with wide and long metaventral process, ca. as long as metaventrite between meso- and metacoxae. Posterior margin of mesocoxae with a postcoxal ridge which does not continue to metaventral process. Median portion of metaventrite slightly elevated, with sparse pubescence similar to lateral portions of metaventrite, without surface microsculpture. Posterior half of metaventrite with fine longitudinal median carina. Metanepisternum narrow, ca. of the same width throughout, sparsely pubescent, with wide and long posterolateral process contacting abdomen. Apterous species.

Legs rather short, tips of femora not overlapping body outline. Procoxa subglobular, sparsely pubescent; profemur with sharply defined tibial groove; protibia cylindrical, with strong apical spines and a sparse series of lateral spines; protarsus densely pubescent ventrally, protarsomere 1 longest, ca. 2 × longer than each subsequent tarsomere. Mesocoxae rather widely divided from each other by metaventral process, transverse; metacoxae transverse, contiguous medially; meso- and metafemora rather wide basally, with sharply defined tibial grooves in distal half, ventral surface without hydrophobic pubescence, only with sparsely arranged setae; meso- and metatibiae slightly bent outwards, slightly widened distally, with short but stout spines distally and along lateral and mesal faces; meso- and metatarsomere 1 the longest, ca. 1.5-2.0 × as long as tarsomere 2; ventral face with dense pubescence, dorsal face with few isolated long setae.

Abdomen with 5 ventrites, all ventrites without median carina, abdominal apex without emargination or series/group of enlarged setae. All ventrites with dense hydrofuge pubescence.