Octomeristes Liu & Beaver, 2016

Liu, Lan-Yu, Beaver, Roger A. & Sanguansub, Sunisa, 2016, A new Oriental genus of bostrichid beetle (Coleoptera: Bostrichidae: Xyloperthini), a new synonym and a lectotype designation for Octodesmus episternalis (Lesne, 1901), European Journal of Taxonomy 189 (189), pp. 1-12 : 3-6

Octomeristes Liu & Beaver , gen. nov.

urn:lsid:zoobank.org:act:4D659D1D-561C-445C-A256-AFA66495D93C

Type species

Octomeristes pusillus Liu & Beaver , gen. et sp. nov., here designated.

Diagnosis

A member of the tribe Xyloperthini , characterized by the lamelliform intercoxal process of the first abdominal ventrite, and the mandibles crossed at the tips ( Lesne 1901; Fisher 1950; Liu & Schönitzer 2011). Distinguished from other genera of Xyloperthini by the following combination of characters: Frons weakly convex, without a crown of hairs on the head in either sex. Mandibles symmetrical, sharply pointed; antenna with eight antennomeres, the funicle and club each trimerous, antennomeres of club lacking stiff, erect hairs, with two indistinct c-shaped sensory impressions near the apex of antennomeres 6 and 7, but not on the last antennomere; pronotum without a lateral carina; posterior part of elytral disc with more than one pair of costae, each ending in a small process at the upper margin of the elytral declivity; protibiae normal, without small teeth on posterior face; female with third abdominal ventrite projecting over and concealing fourth ventrite, its posterior margin with lobes or teeth; fifth abdominal ventrite of male with pleural pieces.

Etymology

The genus name is masculine, and refers to the eight-segmented antenna.

Description

Body elongate, cylindrical. Head deeply inserted in prothorax, not visible from above. Frons convex or slightly impressed, with scattered, fine, upwardly-directed hairs, which are denser and coarser laterally; fronto-clypeal suture indistinct at sides, impressed in middle; clypeus strongly transverse, anterior margin with a very short median lobe or projection, an emargination on each side of the lobe; labrum transverse with a fringe of hairs along anterior margin. Mandibles subequal, sharply pointed. Eyes small, oval, globose, strongly projecting. Antenna with 8 antennomeres, first antennomere elongate, about twice as long as the oval second, antennomeres 3–5 forming a loose funicle, each antennomere short, strongly transverse, the fifth widest, together slightly shorter than second antennomere; antennomeres 6–8 forming the elongate, compressed club, each antennomere with a dense covering of short, recumbent hairs, two indistinct c-shaped sensory impressions on the surface of antennomeres 6 and 7 near apex, but absent from antennomere 8; antennomeres 6 and 7 subquadrate to subtriangular, subequal in length, last antennomere elongate, oval, length variable from 1.5–1.9 times longer than the previous antennomere, but subequal in width.

Pronotum slightly wider than long, widest about one-third from base, anterior angles with a strong, upcurved tooth on margin, anterior margin between teeth straight, not depressed behind the margin; semicircular area above the anterior margin smooth and without teeth; sides broadly rounded, converging more strongly anteriorly, posterior angles broadly rounded, without a lateral carina, postero-lateral area with fine rugulosities; disc smooth, shining, very indistinctly punctured, glabrous; anterior slope with 3 or 4 large, upcurved teeth antero-laterally on each side behind the marginal tooth, with short, semi-erect hairs between the teeth.

Scutellum, small, punctate. Elytra subequal to pronotum in width, strongly convex, smooth, shining, indistinctly punctured anteriorly, the punctures larger and deeper near the declivity, posterior part of disc with more than one pair of costae, each costa ending in a small tooth or projection at upper margin of declivity; declivity weakly convex, glabrous, the postero-lateral margin emarginate.

Legs subequal in length, procoxae contiguous, mesocoxae narrowly separated; tibiae expanded toward apices, protarsi equal in length to protibiae, meso- and meta-tarsi longer than their respective tibiae.

Intercoxal process of first abdominal ventrite lamelliform. Female with third abdominal ventrite projecting over and concealing fourth ventrite, its posterior margin with lobes or teeth. Last visible abdominal ventrite of male with pleural pieces.

Remarks

The genus Octomeristes gen. nov. (abbreviated here as Om.) is noteworthy because the antennae have only eight segments. The only other genus of Xyloperthini with 8-segmented antennae is Octodesmus Lesne (abbreviated here as Od.). Other xyloperthine genera have 9- to 11-segmented antennae. There are presently four species in Octodesmus : the type species, Od. episternalis ( Lesne, 1901) , Od. parvulus (Lesne, 1897) , Od. minutissimus ( Lesne, 1932) and Od. kamoli Chûjô, 1964 ( Borowski & Wegrzynowicz 2007). The senior author has examined syntypes of Od. episternalis (MNHN), the holotype of Od. parvulus (MNHN), and the holotype of Od.kamoli (KUM). We have been unable to examine type material of Od. minutissimus . However, it has been possible to show (see discussion below) that it should be transferred to Octomeristes gen. nov., and it is considered here as a member of that genus. When Lesne (1932) described Octodesmus minutissimus , he suggested that it formed a link between Octodesmus on the one hand, and the genera Xylion Lesne, 1901 , Xylionulus Lesne, 1901 and Xylobosca Lesne, 1901 on the other. Since then, the genus Xylion has been split up ( Lesne 1940; Vrydagh 1955), and the genus restricted to a more closely related group of seven species ( Vrydagh 1955). Following Lesne’s (1932) suggestion, we compare Octomeristes gen. nov. (including Om. minutissimus comb. nov.) to the four genera listed by him, using Xylion in the restricted sense of Vrydagh (1955) ( Table 1 ). A more wide-ranging study of the genera of Xyloperthini would be valuable, but is beyond the scope of the present paper.

The genus Octomeristes gen. nov. can be distinguished from all other xyloperthine genera by the combination of the 8-segmented antenna, with the funicle length much shorter than the first antennomere of the antennal club, and the thickened and modified third abdominal ventrite, which overlaps and conceals the fourth ventrite. Octomeristes gen. nov. is further distinguished from Octodesmus by the absence of sensory impressions on the apical segment of the antennal club (present in Octodesmus ), the sculpture of the elytra ( Table 1 ), and the presence in the male of well-developed pleural pieces (absent in Octodesmus ). It is likely that the reduction in the number of antennal segments in the two genera is related to the small size of the species, and is not an indication of a close relationship. Xylion , Xylionulus and Xylobosca all have 10-segmented antennae.

The genus Xylobosca is distinguished from Octomeristes gen. nov. and the other genera considered here by the form of the protibia, which is atypical for the Xyloperthini , and is widest towards the middle (not at the apex), and lacks a flat external face. The sexual dimorphism of the elytra of Xylobosca is also quite different from Octomeristes gen. nov. However, it is interesting to note the presence of a pair of spines on the fourth ventrite of the female in some species of Xylobosca , as in Octomeristes gen. nov. The genus Xylion is distinguished from Octomeristes gen. nov. and the other three genera by the presence of a lateral carina at the posterior angles of the pronotum, and the remarkable enlargement and modification of the second abdominal ventrite of the female.

The genus that is morphologically most similar to Octomeristes gen. nov. is Xylionulus , with very similar distinguished by

characters of the frons, pronotum and elytra ( Table 1 ). However, the two genera can be characters of the antennae ( Table 1 ), and the modification of the fourth and fifth ventrites of the female abdomen in Xylionulus and not the third ventrite.

Xylion and Xylionulus are Afrotropical genera, Xylobosca is an Australian genus, whilst Octodesmus and Octomeristes gen. nov. are Oriental genera, but the morphological similarities of the five genera might indicate a common origin in Gondwana.

Distribution

India, northern Thailand.

Tables

Table 1. Comparison of characters of Octomeristes Liu & Beaver with selected genera of Xyloperthini.

Genus
	Octomeristes gen. nov.	Octodesmus Lesne, 1901	Xylionulus Lesne, 1901	Xylobosca Lesne, 1901	Xylion Lesne, 1901
Character
No. of antennal segments	8	8	10	10	10
Funicle length relative to 1 st antennomere of club	Much shorter	Subequal	A little longer	More than half the length	Equal in length
Sensory impressions on club	Two indistinct c-shaped impressions on 1 st and 2 nd antennomeres of club	Two distinct circular sensory impressions on each anten- nomere of club including apical	Two large distinct impres- sions on each face of 1 st and 2 nd antennomeres of club	Two zones of concentration of sensory pores on 1 st and 2 nd antennomeres of club	Without distinct impressions, only areas with denser pores
Fronto-clypeal suture	Indistinct at sides, impressed in middle	Obsolete or scarcely visible at side, strongly deepened and foveolate in middle	Indistinct at sides, impressed in middle	Male: distinct, foveiform in middle Female: very fine or indis- tinct	Very distinct
Posterior angles of pronotum	Without lateral carina	Without lateral carina	Without lateral carina	Without lateral carina	With lateral carina
				Male: elytral declivity with
Elytral sculpture	Each elytron with two or three costae on upper margin of declivity	Elytral declivity with a single large spine on each elytron	Elytral declivity bidentate on each side at the upper margin	or without a pair of strong spines Female: elytral declivity	Apical declivity with 4 apophyses or marginal tubercles on each side
				without distinct upper margin
Margin of elytra	Emarginate	Not emarginate	Emarginate or not	Male: not emarginate Female: emarginate	Emarginate
	3 rd ventrite thickened and			1 st ventrite enlarged; 4 th and
Modified ventrites of female abdomen	modified, overlapping and concealing 4 th ventrite; lat- ter with a pair of spines on	4 th ventrite with a pair of spines on posterior margin	4 th and 5 th ventrites variously modified	5 th ventrites emarginate in middle posteriorly; 4 th ven- trite with a pair of spines in	1 st and 2 nd ventrites enlarged; 2 nd to 5 th variously modified
	posterior margin			some species
Male abdomen	5 th ventrite with well-devel- oped pleural pieces	5 th ventrite without pleural pieces	5 th ventrite with well-devel- oped pleural pieces	5 th ventrite with wide pleural pieces	5 th ventrite with more or less developed pleural pieces
Protibia	Wider at apex than in Wider at apex than in middle, Wider at apex than in middle, middle, external face more or external face flattened external face flattened less flattened			Wider at apex than in Widest towards middle, middle, external face more or without a flat face externally less flattened
Protarsi	Male: with shorter and straighter hairs. Female: with long, curving hairs on ventral side	Male: with shorter and straighter hairs. Female: with long, curving hairs on ventral side	A fringe of short hairs on ventral side in both sexes	Male: without modified hairs. Female: with long erect hairs on inner side	Male: with fairly long but straight hairs. Female: with longer, curving hairs on ventral side
Geographical distribution	Oriental	Oriental	Afrotropical	Australian	Afrotropical