Ptomaphaminus Perreau, 2000

Schilthuizen, Menno, Perreau, Michel & Njunjic, Iva, 2018, A review of the Cholevinae from the island of Borneo (Coleoptera, Leiodidae), ZooKeys 777, pp. 57-108 : 78

Genus: Ptomaphaminus Perreau, 2000

Notes.

During the study of this Bornean material, we have refined our concept of the genus Ptomaphaminus , which is why the genus description below is more extensive than for the previous genera.

Description.

Species of small size, not exceeding 2 mm. Colour generally brown, partly yellowish or light brown, rarely darker. Dorsal surface covered with short recumbent setae inserted along transverse strigae which also cover the whole dorsum of the body. Head with more or less developed eyes. A significant eye reduction is observed in species living in subterranean environments. Antennae generally slender, the apical club weakly marked. Pronotum transverse, the largest width generally at the base, the sides of the pronotum and the elytra continuously arcuate, of equal width. Elytra generally elongate, the posterior sutural angles rounded in males (Figure 14a), in females either rounded (Figure 14b), or simply angular (Figure 14c), or sharply protruding backwards (Figure 14 d–e). Surface of elytra with transverse oblique strigae and a single longitudinal sutural stria. Flight wings generally present and functional, even in species living in subterranean environments. (The few apterous or brachypterous species of the genus do not live in Borneo.) Mesoventral process low, narrow, and rounded. Metasternal sutures incomplete and convergent towards the central axis of the body. Protibiae with a lateral row of spines along the external edge and with smaller spines randomly dispersed on the ventral side. Mesotibiae and metatibiae with a circular row of spines around the apex. Male protarsi with four protarsomeres expanded, female protarsi unexpanded. Male and female mesotarsi and metatarsi unexpanded. Male genital segment (urite IX) with a long spiculum gastrale, significantly extending beyond the anterior margin of the epipleurites and sometimes expanded into a paddle shape in the distal half. The size of the aedeagus (relatively to the body length) is highly variable: from 3.0 ( P. latescens ) to 5.7 ( P. marshalli ) times smaller than the body length. The left apical expansion of the median lobe generally (in Borneo species) with a more or less developed, ventrally deflexed and sometimes retroverted apical hook, clearly visible in lateral view, more rarely simple ( P. latescens , P. testaceus sp. n.). Endophallus with a long and weakly sinuate stylus and with a basal symmetric (Figures 12a, 12c) or asymmetric (Figures 12f, h, j, l, m, o, q, s, w, y) loop. When asymmetric, the loop is expanded on the left side in dorsal view (which appears on the right side on pictures which are traditionally illustrated with the caudal side up). Female genital segment either with long gonocoxites, more than three times as long as wide ( P. latescens : Figure 13b; P. testaceus sp. n.: Figure 13d), or gonocoxites reduced to small subsquare sclerites (Figures 13f, h, j, n, p, s, u). Spermatheca generally bilobate, with ( P. ater Perreau, 2009: Figure 13f) or without an apical sclerified plate. A single lobe, weakly sclerotised and transversally ringed occurs in P. latescens (Figure 13b) and P. testaceus (Figure 13d). Spermiduct less sclerotised, but generally with a fixed morphology, sometimes wrapped in a helical shape, rarely entirely membranous, without structured morphology ( P. hanskii sp. n., P. sarawacensis sp. n.: Figures 13 h– 13j).

Remarks.

The two species P. latescens and P. testaceus sp. n. have significantly different morphological characters from other species of Ptomaphaminus (not limited to Borneo): a short stylus of the endophallus (limited to half the length of the median lobe) with a symmetric basal loop, female gonocoxites long (more than three times longer than wide), a weakly sclerified spermatheca with a set of transversal rings (similar to structures preventing a collapse under depression, like for the respiratory trachea). Other species have a long stylus developed on most of the length of the aedeagus, female gonocoxites short, sub-square and a more sclerified spermatheca without reinforcing transversal rings. These two species form a distinct species group which possibly represents another genus.

Biology.

Little information is available on the biology of Ptomaphaminus . Two methods of sampling are successful in obtaining specimens: trapping with pitfall traps baited with meat, cheese, or human excrement (either in epigean or in cave environments) and manual collecting in caves. Species collected in epigean conditions generally have fully developed eyes and flight wings while specimens from caves often have reduced eyes (although presently no anophthalmic Ptomaphaminus are known). The eye reduction observed in species recorded from caves is not correlated with the flight wing reduction, in contrast to palaearctic and nearctic subterranean species of Cholevinae ( Leptodirini ; Ptomaphagus (Adelops) ). Flight wings of P. fagei Perreau, 2009 and P. latescens Szymczakowski, 1964, for example, remain fully functional as observed in Gua Sedepan (Eastern Kalimantan) and caves in the Kinabatangan valley (Sabah) where specimens flew up when lighted by headlamps even in the dark zone deep inside caves. A similar observation was reported by Peck (1981) for P. chapmani Peck, 1981.

Species are very similar externally. For each of the species below, we provide only specific diagnoses, without listing any shared generic characters.