Review of Coelostoma of the Indian subcontinent (Coleoptera: Hydrophilidae) Part 1: Coelostoma s. str. and Holocoelostoma

Abstract

Species of the genus Coelostoma Brullé, 1935 belonging to the subgenera Coelostoma s. str. and Holocoelostoma Mouchamps, 1958 from the Indian subcontinent are revised. Six species of Coelostoma s. str. and two species of Holocoelostoma are recognized, of which two are described as new: C. (Coelostoma) lyratum sp. nov. (India: Maharashtra) and C. (Coelostoma) nostocinum sp. nov. (India: Maharashtra, Goa, Karnataka, Kerala). Coelostoma (Coelostoma) fallaciosum Orchymont, 1936 and C. (Coelostoma) vividum Orchymont, 1936 were recorded for the first time from India and Bangladesh, respectively. Lectotypes are designated for C. aeneolum Régimbart, 1903 and Hydrobius stultus Walker, 1858. The previously confusing situation with Coelostoma (Holocoelostoma) stultum (Walker, 1858) and C. (Holocoelostoma) bhutanicum Jayaswal, 1972 is clarified based on new material of both species from India. Coelostoma sulcatum Pu, 1963 from China is removed from the synonymy of C. stultum and considered as a likely synonym of C. bhutanicum, a status which needs to be confirmed by a detailed study of type specimens. All species are (re)described and illustrated. Diagnosis of the subgenera of Coelostoma are modified in order to accommodate the species of the Indian subcontinent, resulting in narrowing down the concept of Coelostoma s. str. and widening the concept of Lachnocoelostoma Mouchamps, 1958.

Additional fauna of Coelostoma Brullé, 1835 from China, with re-establishment of Coelostoma sulcatum Pu, 1963 as a valid species (Coleoptera, Hydrophilidae, Sphaeridiinae)

“… Coelostoma sulcatum Pu, 1963 is morphologically variable in shape of aedeagus, especially in parameres. Compared with the original description ( Jayaswal 1972 ) and photos of C. bhutanicum from india ( Sheth et al 2020 ), C. bhutanicum is very similar to C. sulcatum especially in aedeagus, which outer face of median lobe is slightly narrowing or subparalleling from base to apical fourth and distinctly narrowed subapically (Fig. 10B–I ).…”

“…Jia et al (2014) thought this species was a synonym of Coelostoma stultum Walker. Liu et al (2020) and Sheth et al (2020) stated that it is a different species from C. stultum Walker after they studied a paratype of C. stultum , and considered as a likely synonym of Coelostoma bhutanicum Jayaswal, 1972 ( Sheth et al 2020 ). Here, we recovered the status of C. sulcatum Pu as a valid species.…”

“…Occasionally, some species can be found in small puddles. Adults usually are active at night and exhibit phototaxis ( Hansen 1999 ; Jia 2005 ; Short and Hebauer 2006 ; Short and Fikáček 2011 ; Jia et al 2014 , 2017 , 2019 ; Liu et al 2020 ; Sheth et al 2020 ). In the Nearctic and Neotropical regions, Coelostoma is replaced by the genera Phaenonotum Sharp, 1882, Phaenostoma Orchymont, 1937 and Lachnodacnum Orchymont, 1937 ( Gustafson and Short 2010 ; Deler-Hernández et al 2013 ; Clarkson et al 2014 ; Jia et al 2014 ).…”

“… Coelostoma can be separated from other genera of Coelostomatini by following characters combined: broadly oval and convex body shape; loosely segmented antennal club; prosternum convex medially; mesoventrite with an elevated arrowhead-shaped process in the middle; metaventral process projecting anteriorly between mesocoxae, abutting mesoventral elevation; the first metatarsomere distinctly longer than the second one; elytra with dense punctures and sutural stria, without serial punctures in most species; the first abdominal ventrite with or without carina medially (e.g., Jia et al 2014 ; Sheth et al 2020 ).…”

“…Among these species, Coelostoma transcaspicum Reitter, 1906 reported by Orchymont (1925) from Shandong is doubtful ( Balfour-Browne 1951 ). Sheth et al (2020) removed C. sulcatum Pu, 1963 from the synonymy of C. stultum (Walker, 1858) and considered it as a likely synonym of C. bhutanicum Jayaswal. Hence the status of C. sulcatum Pu, 1963 is now unclear.…”