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

Figures 4A-C , 5A-C

Type material examined.

Holotype: male (SYSU), China, Fujian, Wuyishan, Sangang Village (三港村), 16-28.v.2004, Cai-xia Yuan & Jing Li leg.

Diagnosis.

Length 6.13 mm. Head, pronotum and elytra with similar punctation. Prosternum carinate medially, with a prominent tooth anteromedially. Elytra parallel-sided in the middle, without serial punctures laterally. Mesofemora densely pubescent, except on extreme apex. First abdominal ventrite with median carina on basal one-thirds. Fifth ventrite slightly emarginate and with a row of stout setae apically. Aedeagus (Fig. 5A-C ): very large, similar to Coelostoma vagum Orchymont, 1940, but median lobe narrowly rounded apically, apex without a sharp prominent tooth ventrally; parameres abruptly widened apically, distinctly bent inward.

Description.

Form and colour (Fig. 4A-C ). Total length 6.13 mm; maximum width 3.3 mm; body broadly oval, parallel-sided in the middle, moderately convex. Dorsum black and shiny. Labrum, maxillary palpi and labial palpi reddish brown, antennae yellowish to reddish brown with dark club. Ventral surface reddish brown to black. 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, distinctly emarginate anteriorly in lateral view, separated by ca. 4 × the width of one eye. Mentum strongly emarginated anteriorly and depressed in anterior half, with sparse fine punctures. 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 a prominent tooth anteromedially. Scutellum in shape of equilateral triangle, with punctures finer and denser than those on pronotum. Elytra with punctures as on pronotum; elytra without serial punctures; sutural stria reaching anterior half of elytra; lateral margin of elytra with bead but not 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 distinct median carina on basal one-thirds. Fifth ventrite with fine marginal bead and slightly emarginate apically.

Male genitalia (Fig. 5A-C ). Aedeagus very large, 2.3 mm long. Median lobe widest at midlength, ca. 5 × as long as wide; median lobe gradually narrowing towards apex, with a small finger like apex, narrowly rounded apically; gonopore rounded, situated subapically; parameres much longer than the median lobe, abruptly widened apically, distinctly bent inward.

Etymology.

This species is derived from the Latin verb mixtus, mix, refers to the fact that this species is similar to Coelostoma vagum Orchymont, 1940 in shape of the median lobe and similar to C. wui Orchymont, 1940 in shape of parameres.

Biology.

Unknown, this species was collected with C. wui Orchymont, 1940 in the same place.

Remarks.

The holotype of this species was identified as C. vagum Orchymont, 1940 in Jia et al. (2017). However, it is different from C. vagum in the form of the aedeagus. Hence, the distribution of C. vagum in Fujian needs to be verified. This species is the seventh known species of the Coelostoma phallicum group. This group can be recognized by a large and very elongate aedeagus with an extremely reduced phallobase and large subapical gonopore ( Liu et al. 2020). This species is most similar to C. vagum Orchymont, 1940 (Fig. 5D-F ) and C. bipunctatum Jayaswal, 1972 in shape of the median lobe but can be distinguished from them by the narrowly rounded apex of median lobe (apex pointed in C. vagum and C. bipunctatum ), median lobe widest in the middle (median lobe nearly parallel-sided in the middle in C. vagum and C. bipunctatum ). It also can be distinguished from C. vagum by apex of median lobe without a sharp prominent tooth ventrally (Fig. 5B ) (apex with a sharp prominent hook-shaped tooth ventrally in C. vagum (Fig. 5E ))

Distribution.

Only known from type locality. China (Fujian).

Figures

Figure 4. Coelostoma (Lachnocoelostoma) mixtum Mai & Jia, sp. nov. A dorsal view B ventral view C lateral view. Scale bar: 1.0 mm (A-C).

Figure 5. Aedeagus of Coelostoma mixtum Mai & Jia, sp. nov. and Coelostoma vagum Orchymont, 1940. A-C C. mixtum sp. nov. A dorsal view B lateral view C ventral view D-F C. vagum D dorsal view E lateral view F illustration by Orchymont (1940). Scale bar: 0.5 mm (A-E).