Allohoraeomorphus Franz

Jałoszyński, Paweł, 2012, Taxonomic status of Allohoraeomorphus Franz (Coleoptera, Staphylinidae, Scydmaeninae), Zootaxa 3313, pp. 62-68 : 63-64

Status of Allohoraeomorphus Franz

Franz (1986a) treated Allohoraeomorphus as closely related to Horaeomorphus and his diagnosis was based on differences found in the structure of mesoventrite and pronotal base. Diagnostic characters of Horaeomorphus originally given by Schaufuss (1889) were recently redefined by Jałoszyński (2002, 2003, 2004a) and include the typical slender and constricted body form (the "ant-like" appearance); the occipital part of head ("neck" region) broad; antennae gradually thickened distally, distinctly 11-segmented; the pronotum without lateral carinae, with ante-basal foveae; the prosternal process narrow, weakly separating procoxae; the mesoventral process distinct but weakly projecting ventrally; each elytron with two small basal foveae (in intact specimens concealed by the pronotal base); femora clavate; the aedeagus with free parameres and a complex endophallus. Additionally, nearly all species of Horaeomorphus have a pair of lateral pits on the frons, and some species show a distinct sexual dimorphism in the development of metatrochanters. The hind trochanters of males are often strongly elongated and forming a long rod-like projection running along femur, the trochanter in some cases exceeds half length of metafemur. Among Scydmaeninae , only a single species of Syndicus ( Jałoszyński 2004b) and A. calcarifer have similarly shaped male metatrochanters.

Examination of a male paratype of A. calcarifer and direct comparison with H. eumicroides revealed a number of characters shared by these two taxa, and only minor differences. Allohoraeomorphus calcarifer ( Fig. 1) is a large, darkly pigmented species, in body shape resembling H. sarawakensis Franz, 1992 (from W and E Malaysia), H. valdepunctatus Franz, 1984 (W Malaysia), H. punctatissimus Franz, 1992 (E Malaysia, Indonesia), H. fakfakensis Jałoszyński, 2009 (New Guinea) and H. samosirensis Jałoszyński, 2009 (Sumatra) . All these species have strikingly large pronotum, in dorsal view nearly circular and nearly as broad as elytra. Most species of Horaeomorphus are brown, but such unusually dark, nearly black body pigmentation as that of A. calcarifer can also be found within this genus, e.g. in H. blattnyi Jałoszyński, 2004a (from Luzon, Philippines).

The lack of posterolateral pronotal corners, mentioned by Franz (1986) as one of two diagnostic characters of Allohoraeomorphus , was apparently misinterpreted. The pronotum of A. calcarifer , although with strongly rounded sides, has distinct, obtuse hind angles. This character is developed to a similar extent as in all species of Horaeomorphus with broad pronota.

The other diagnostic character mentioned by Franz (1986), the shape of mesoventral process, which is weakly ( Allohoraeomorphus ) or strongly ( Horaeomorphus ) expanded ventrally, is problematic. In A. calcarifer ( Figs. 2, 3 ) this process (msp) is indeed shorter and lower (i.e., less expanded ventrally) than in H. eumicroides ( Figs. 4, 5 ), or in all other species of Asian Horaeomorphus previously studied by the author. However, the general shape of the mesoventral process and the structure of the entire mesoventrite in A. calcarifer and in H. eumicroides are similar. The difference in the shape of mesoventral processes is too small to unambiguously define the length and height that could be diagnostic for either genus.

The diagnostic characters used by Franz (1986a) to define Allohoraeomorphus are insufficient to distinguish this genus from Horaeomorphus . However, two additional differences were found during the present study. As seen in Figs. 2–5 , the prothoracic basisternum (bs) of the compared species differs in length—that in A. calcarifer is longer than procoxae, while that of H. eumicroides is distinctly shorter. Also the prosternal process (pp) of A. calcarifer is longer than that of H. eumicroides . However, it is difficult to define a clear-cut limit between two genera on the basis of a shorter or longer basisternum alone. Such length differences in Scydmaeninae , if not correlated with other significantly different structures, are generally treated as a morphological diversity within a genus, and not as generic diagnostic characters.

Another difference between A. calcarifer and H. eumicroides is the lack of pits on the head of the former species. The frons of nearly all species of Horaeomorphus , including H. eumicroides , bears variously developed, but usually well-visible lateral pits, each located at the posteromesal margin of supraantennal tubercle (illustrated in Jałoszyński, 2003; figs. 2A, B). This character was included in the generic diagnosis ( Jałoszyński 2002, 2003), but subsequent revisions revealed a significant extent of variability in diameter and depth not only between, but also within species. For instance, the pits in H. sarawakensis are shallow and in some individuals can be barely discernible ( Jałoszyński, 2006). It seems that the depth of pits correlates with the development of supraantennal tuber-cles—in species with weakly raised tubercles the pits are shallow or indistinct. The supraantennal tubercles are weakly raised in A. calcarifer , and additionally its frons and vertex are more convex than in Asian Horaeomorphus . The presence or lack of pits may be misleading and should not be treated as a primary diagnostic character of Horaeomorphus .

In conclusion, the previously listed unique characters of Allohoraeomorphus were found to have little diagnostic value, and the observed differences between A. calcarifer and H. eumicroides can be treated as variable within Horaeomorphus . Therefore, Allohoraeomorphus is placed as a junior objective synonym of Horaeomorphus :

Figures

FIGURES 2 – 5. Body venter of Horaeomorphus calcarifer comb. n. (2, 3) (abdomen removed) and Horaeomorphus eumicroides Schaufuss (4, 5). Abbreviations: bs — prothoracic basisternum; hy — prothoracic hypomeron; msp — mesoventral process; msv — mesoventrite; mtp — metaventral process; mtv — metaventrite; pp — prosternal process. Scale bars: 1 mm.