Holotype : ♂, Japan, Kagoshima Prefecture, Toshima Village, Tokara Islands, Tokara-Nakanoshima Island, Nanatsuyama, 7.VII.2019, leg. Naomichi Tsuji, “under permission” (EUMJ).

According to Merkl (1992), the epistome structures of males are important diagnostic characteristics for Platycotylus species. All known Platycotylus males present a pair of short tubercles at the middle of the epistome, except for Platycotylus palmi Ferrer, 1998 (absent; see Ferrer 1998). Therefore, aside from species of which males have not been examined [Platycotylus parvicollis (Pic, 1923) and Platycotylus tenuicollis (Fairmaire, 1893)], this new species can be distinguished from all other males of congeneric species by its long and asymmetrical epistomal horn.

The new species is most similar to P. parvicollis, of which a male has not yet been examined. It can be distinguished by the simple sparse punctation on the pronotum (laterally rugulose in P. parvicollis; see Merkl 1992) and by elytra that are scarcely striate, with elytral intervals that are neither convex nor carinate (striate in the original description of P. parvicollis; Pic 1923). Additionally, the smaller eyes and acutely produced temples of the new species differ from those of P. parvicollis.

In addition, the umbilical tubercle on the center of mentum may be one remarkable characteristic of this new species. At least, there is no such tubercle on the mentum of P. nitidulus, which has a small fovea in the middle.

Body length: 3.40 mm. Male. Elongate and flattened, shiny; dark reddish brown, head and pronotum blackish brown, elytra darkened on sutural and lateral parts.

Head obtrapezoidal, weakly convex, without frontogenal and frontoclypeal sutures; punctures coarse and dense, partly piligerous; epistome with a large asymmetrical horn in middle, distinctly emarginate on both sides of the horn, which is distinctly curved to the left and acute at its apex, with a long yellow seta arising from each emarginated anterior margin, covered with punctures; genae convex, roundly produced laterad; frons broadened, weakly convex, slightly sloping forwards, 3.83 times as wide as width of eye in lateral view; eyes entirely lateral, strongly convex laterad, without inner ocular sulci; temples slender, acutely produced laterad, setiferous and finely punctate. Antennae slender, surpassing base of elytra, almost filiform though 7^th antennomere dilated apicad and 8^th to 10^th ones dilated and nearly as long as wide; 11^th antennomere elongate. Ultimate maxillary palpomeres fusiform. Mentum transversely quadrate, weakly convex, irregularly depressed at sides, with an umbilical tubercle at middle. Submentum flat, subquadrate, strongly emarginate at sides. Gula narrow, linguiform, unevenly flat and smooth.

Pronotum obtrapezoidal, widest at apical fifth and 1.30 times as wide as long; disc slightly convex, densely punctate, punctures piligerous laterally, nearly as large as and slightly sparser than on head; anterior margin subtruncate, unbeaded; anterior corners with an acutely pointed process; lateral margins slightly rounded and evenly convergent posteriad, almost invisible in dorsal view, roundly and weakly edged at apical fifth and basal fifth, slightly sinuate before base, very finely beaded; posterior corners with processes smaller than those on anterior corners and acutely pointed laterad; basal margin weakly rounded, moderately beaded. Scutellar shield transverse, 1.67 times as wide as long, surface flat and smooth.

Elytra elongate, subparallel-sided, widest at basal sixth and 2.14 times as long as their combined width, subvertical between 7^th intervals and lateral margins; surface scarcely striate, with rows of punctures larger than on pronotum; intervals almost flat and impunctate; epipleura irregularly rugulose.

Prothoracic hypomera weakly depressed, with large and coarse piligerous punctures. Prosternum weakly convex, distinctly sulcate along apical bead, sparsely punctate in middle and moderately so laterally; prosternal process trapezoidal, depressed, coarsely punctate. Mesoventrite weakly convex, with large and sparse piligerous punctures. Metaventrite weakly convex, sparsely and evenly punctate though becoming denser and piligerous in each lateral fourth. Abdomen (Fig. 2A) with punctures piligerous, fine and dense; lateral margins of 3^rd and 4^th ventrites weakly and roundly produced in each apical half; 5^th ventrite evenly rounded at posterior margin.

Figure 2. 

Abdominal segments of Platycotylus merkli sp. nov., holotype, male A Ventrites B 8^th segment, ventral view C 9^th sternite, ventral view. Scale bars: 1.0 mm a (A); 0.5 mm (B, C).

Abdominal sternites VIII and IX (Fig. 2B, C); sternite VIII thin, with short setae along posterior margin; sternite IX with a pair of horizontally elongate sclerites, with an elongate protrusion on the apical third of each sclerite that is slightly curved inwards. Aedeagus (Fig. 3) lanceolate, very short, 0.11 times as long as elytra, slightly twisted towards left side of body, obsoletely margined between basale and apicale; basale 1.07 times as long as apicale; apicale rounded at apex.

Figure 3. 

Aedeagus of Platycotylus merkli sp. nov., holotype A, B Dorsal C dorsolateral D ventral. Scale bars: 0.5 mm a for A; b for B–D.

Legs robust. Femora strongly dilated towards middle or distally, sparse with setiferous punctures. Tibiae short and slender; protibiae with two tibial spurs, one of which is very large and robust, curved posteriorly.

Female. Unknown.

The new species is dedicated to the late Dr Ottó Merkl, who made a significant contribution to the taxonomy of Tenebrionidae.

Japan: Tokara Islands (Nakanoshima Island).

The holotype was collected by beating the dead branches of an unidentified living tree.