Coelostoma (Lachnocoelostoma) dactylopunctum Mai & Jia, 2022

Mai, Zuqi, Hu, Jian & Jia, Fenglong, 2022, Additional fauna of Coelostoma Brulle, 1835 from China, with re-establishment of Coelostoma sulcatum Pu, 1963 as a valid species (Coleoptera, Hydrophilidae, Sphaeridiinae), ZooKeys 1091, pp. 15-56 : 15

Coelostoma (Lachnocoelostoma) dactylopunctum Mai & Jia sp. nov.

Figures 2A-E , 12A

Type material examined.

Holotype: male (SYSU), China, Yunnan, Honghe Hani and Yi Autonomous Prefecture, Lvchun County, Huanglianshan Mountain, Huanglianshan Reservoir (黄连山水库), 22.8898°N, 102.2952°E, 1717.3 m, 30.iv.2021, in a forest stream at night, Jiang, Yang, Huang & Mai leg. Paratypes: 2 males (SYSU), same data as the holotype.

Diagnosis.

Length 4.3-4.5 mm. Head and pronotum with similar punctation. Prosternum carinate medially, with a fine tooth anteromedially. Elytra not parallel-sided in the middle, each elytron with ten distinct rows of serial punctures; intervals between series with two sizes of punctures especially in posterior half of elytron, the finer punctures as on pronotum and much finer and shallower than the coarser punctures, coarser punctures almost as coarse as those of the series (Fig. 12A ). Mesofemora densely pubescent, except on extreme apex. First abdominal ventrite with complete median carina. Fifth ventrite slightly emarginate and with a row of stout setae apically. Aedeagus (Fig. 2D, E ): 0.87 mm long. Median lobe emarginate apically, outer face nearly parallel-sided from basal to middle, then gradually narrowing towards apex, gonopore situated subapically, wider than long. Parameres slightly longer than median lobe, gradually expanded from anterior fourth to apex, broadly truncate apically, inner apical angle acute, pointed; middle part of parameres ca. 0.5 × as wide as median lobe at the same level.

Description.

Form and colour (Fig. 2D, E ). Total length 4.3-4.5 mm (holotype: 4.5 mm); maximum width 2.8-3.0 mm (holotype: 3.0 mm); body broadly oval, not parallel-sided in the middle, moderately convex. Dorsum black to reddish brown, with lateral margin of pronotum and elytra paler. Labrum, maxillary palpi and labial palpi reddish brown, antennae yellowish to reddish brown with dark club. Ventral surface reddish brown. Femora and tibiae dark reddish brown, tarsi pale reddish.

Head. Dorsal surface with dense fine punctures. Interstices between punctures smooth. Clypeus subtruncate anteriorly. Eyes of moderate size, slightly emarginated anteriorly in lateral view, separated by ca. 5.3 × the width of one eye. Mentum emarginate anteriorly and depressed in anterior half, with sparse punctures except on the depressed portion. Antennae with nine antennomeres, antennal club (antennomeres 7-9) densely pubescent. Maxillary palpomere 2 strongly swollen, palpomere 4 truncate apically, slightly longer than palpomere 3. Gula narrow and glabrous.

Thorax. Pronotum widest posteriorly, gradually narrowed anteriad, with punctures as on head, anterolateral angles obtusely rounded, posterolateral angles blunt, anterior and lateral margins with narrow marginal bead. Prosternum with a carina medially and slightly projecting anteromedially. Scutellum in shape of equilateral triangle, with punctures as on pronotum. Each elytron with ten distinct rows of serial punctures; intervals between series with two sizes of punctures especially in posterior half of elytron, the finer punctures as on pronotum and much finer and shallower than the coarser punctures, coarser punctures almost as coarse as those of the series (Fig. 12A ); series 1 and 2 reaching basal half of elytron, series 1 overlap with sutural stria; series 3 and 4 nearly reaching elytral base and fused together subposteriorly; series 5-10 reaching elytral base, slightly sulcate posteriorly; the outer four serial punctures coarser and stronger than the inner six serial punctures (Fig. 12A ). Lateral margin of elytra with bead and slightly explanate.

Legs. Pro- and mesofemora bearing dense pubescence, except on extreme apex. Metafemora not pubescent, with dense microsculptures and spares fine punctures. Meso- and Metatibia slightly flattened, with strong apical spurs and series of sparse stout spines laterally. Tarsi with long dorsal setae and gold ventral setae; metatarsi with fifth tarsomere almost as long as third and fourth combined. Claws curved, with a pair of long setae beneath.

Abdomen. Abdominal ventrites densely pubescent. First ventrite with complete median carina. Fifth ventrite slightly emarginate and with fine marginal bead, with a row of stout setae apically.

Male genitalia (Fig. 2D, E ). Aedeagus ca. 0.87 mm long. Median lobe emarginate apically, widest basally, ca. 3.5 × as long as wide; outer face nearly parallel-sided from base to middle, then gradually narrowing towards apex; gonopore situated subapically, wider than long. Parameres slightly longer than median lobe, gradually expanded from anterior fourth to apex, broadly truncate apically, inner apical angle acute, pointed; middle part of parameres ca. 0.5 × as wide as median lobe at the same level.

Etymology.

The species name is a combination of Dactylosternum , a genus in the same tribe Coelostomatini , and the Latin punctum. The name refers to the fact that this species with distinct serial punctures on elytra which is similar to many species of Dactylosternum Wollaston, 1854.

Biology.

Aquatic. Adults were found on the edges of a forest stream at night.

Remarks.

This species is easily recognized as a member of Dactylosternum by the ten rows of serial punctures on elytra, which is different to any known Coelostoma species. Coelostoma martensi Hebauer, 2002 and C. gentilii Jia, Aston & Fikáček, 2014 (Fig. 13B ) are also known with serial punctures on elytra, but only visible laterally. Coelostoma rubens Hebauer, 2002 ( Jia et al. 2019: figs 4, 5), C. jaculum Jia, Angus & Bian, 2019 ( Jia et al. 2019: figs 2, 3) and C. phototropicum Jia, Angus & Bian ( Jia et al. 2019: fig. 1) are similar to this new species in the shape of aedeagus. However, none of these species with serial punctures on elytra.

Distribution.

Only known from type locality. China (Yunnan).

Figures

Figure 2. Coelostoma (Lachnocoelostoma) dactylopunctum Mai & Jia, sp. nov. A dorsal view B ventral view C lateral view D, E aedeagus (D dorsal view E ventral view). Scale bars: 1.0 mm (A-C); 0.5 mm (D, E).

Figure 12. Lateral view of Coelostoma spp. (the red figures indicate the serial number of elytral serial punctures; the white arrows indicate the punctures of series; the circles indicate the coarser punctures; the squares indicate the finer punctures) A Coelostoma dactylopunctum sp. nov. B Coelostoma fortunum sp. nov. Scale bar: 1 mm (A, B).

Figure 13. Lateral view of Coelostoma spp. (the red figures indicate the serial number of elytral serial punctures; the white arrows indicate the punctures of series; the square indicates the elytral ground punctures) A Coelostoma pseudomartensi sp. nov. B Coelostoma gentilii Jia, Aston & Fikacek, 2014. Scale bar: 1 mm (A, B).