Hypocacculus Bickhardt, 1914

Lackner, Tomáš, 2010, Review of the Palaearctic genera of Saprininae (Coleoptera: Histeridae), Acta Entomologica Musei Nationalis Pragae (suppl.) 50, pp. 1-254 : 122-124

Hypocacculus Bickhardt, 1914

Type species: Saprinus metallescens Erichson, 1834 , designated by BICKHARDT (1916: 96).

Hypocacculus Bickhardt, 1914: 311 . Hypocacculus: REICHARDT (1926) : 14; REICHARDT (1932): 28, 96; REICHARDT (1941): 156, 280; PEYERIMHOFF (1936): 228; WITZGALL (1971): 173; MAZUR (1973): 27, 37; KRYZHANOVSKIJ & REICHARDT (1976): 111, 201; MAZUR & KASZAB (1980): 7, 52; VIENNA (1980): 116, 171; MAZUR (1981a): 71, 96; MAZUR (1984): 83; MAZUR (1997): 249; YÉLAMOS (2002): 245, 308; MAZUR (2004): 93.

Diagnosis. Cuticle often metallic, elytra never with red maculae; body size between 1.20–3.00 mm, in most cases smaller than 2.5 mm. Antennal scape never extremely dilated and/or thickened; antennal club without visible articulation. Frontal stria never interrupted; supraorbital stria at times lacking; frontal disc punctate, never smooth and/or with several deep rugae (as in Hypocaccus ). Eyes always visible from above. Pronotum without pronotal foveae, pronotal disc usually with punctation at least laterally, never entirely smooth. Marginal pronotal stria usually complete, lateral pronotal stria always absent; disc of pronotum very convex, so that lateral margins are not observable along their entire length (seen from dorsal view). Prosternum in most cases with pre-apical foveae (apart from Hypocacculus (Colpellus) solieri ( Marseul, 1862)) ; both sets of prosternal striae present. Basal area of metaventrite rarely (e.g. Hypocacculus (Nessus) baudii ( Schmidt, 1890) or Hypocacculus (Nessus) balux Reichardt, 1932 ) with two large tubercles. Protibia usually moderately dilated, outer margin with 6–16 teeth; mesotibia and metatibia usually not particularly thickened.

Differential diagnosis. Hypocacculus is most similar to the presumably closely related genera Chalcionellus , Pholioxenus and Paravolvulus . Actually, Pholioxenus and Paravolvulus were once included in Hypocacculus and in several cases the delimitations between several species included in them and Hypocacculus are not clear-cut. Chalcionellus differs from Hypocacculus mainly by the well-developed pronotal foveae; however, not all taxa included in Chalcionellus possess them. In cases, where there are no pronotal foveae present in Chalcionellus , frontal stria is prolonged onto the clypeus (occasionally clypeus and/or anterior part of frontal disc are depressed) and the body is metallic. From Pholioxenus this genus differs chiefly by the shape of protibia and number of teeth on its outer margin: protibia in Pholioxenus is more dilated than in Hypocacculus and it is usually furnished with 4–6 low, broad teeth, topped with tiny slender denticle (whereas the outer margin of protibia in Hypocacculus is furnished with 6–15 low teeth topped with short denticle) and the pronotum in Pholioxenus is only slightly convex so that its lateral margins are visible along their entire length (seen from dorsal view). Furthermore, the eyes in Pholioxenus are more convex than in Hypocacculus and the elytral surface is often imbricate. Pre-apical foveae are also considerably less developed in Pholioxenus and in several species they are even absent. Sutural elytral stria, especially on its apical half is strongly carinate in many species of Pholioxenus and it is rarely basally connected with fourth dorsal elytral stria (in Hypocacculus the sutural elytral stria is rarely carinate and it is often connected with the fourth dorsal elytral stria). Pholioxenus is a typical inquilinous taxon with all of its known Palaearctic species inhabiting burrows of rodents – this behavior is more an exception than a rule in Hypocacculus . Another presumably closely related genus Paravolvulus differs from the species of Hypocacculus with usually interrupted frontal stria and often present lateral pronotal stria; in several cases the species of Paravolvulus possess red maculae on their elytra (e.g. Paravolvulus fausti Schmidt, 1885a ), which is unseen in Hypocacculus . The cuticle of Paravolvulus is usually not metallic, whereas in Hypocacculus it often is, and eyes in Paravolvulus are more convex than in Hypocacculus .

There are several more genera that could also be confused with Hypocacculus : Zorius , Axelinus , Saprinillus , and in the case of subgenus Nessus even with species of the genus Hypocaccus . Species of the genus Zorius generally differ from Hypocacculus by the larger body size and elevated anterior margin of clypeus, furthermore, the pre-apical foveae in Zorius are absent, whereas they are almost universally present in Hypocacculus . The sole taxon included in genus Axelinus , A. ghilarovi , differs from all species of Hypocacculus by widely interrupted frontal stria, rugulose-lacunose frontal disc and by the shape of protibia: in Axelinus ghilarovi it is with three triangular teeth topped with short broad denticle, followed by two minute denticles and in Hypocacculus the teeth of protibia are usually more numerous. Another very similar genus, Saprinillus , differs from Hypocacculus likewise by the widely interrupted frontal stria, more cylindrical body and the shape of protibia that in the case of Saprinillus bears only denticles and never articulated teeth. Taxa included in the subgenus Nessus of the genus Hypocacculus possess similarly structured frontal disc as some species of Hypocaccus (frontal disc with numerous coarse rugae), but their body size is generally smaller than that of the most Hypocaccus species, and the frontal stria of subgenus Nessus is similarly strongly carinate and straight. According to Mazur (pers. comm. 2008), Nessus ought to be synonymized with Hypocaccus ; however, the two taxa should be first compared using modern phylogenetical methods at the species level, something that is beyond the scope of this paper.

Biology. The species of Hypocacculus are typically collected on carrion and in dung in dry and arid places. Several species (e.g. Hypocacculus (Nessus) eremobius Reichardt, 1932 ) appear to be true psammophiles with their corresponding morphological adaptations.

Distribution. This genus is distributed mostly in the Palaearctic and Afrotropical Regions, with several representatives known also from Indo-Malayan Subregion. Hypocacculus (Hypocacculus) hyla ( Marseul, 1864) has been recorded as far as New Guinea, enriching thus the Australopacific Region; Hypocacculus (Hypocacculus) interpunctatus ( Schmidt, 1885a) has been introduced into Australia ( MAZUR 1997). This genus consists of five subgenera, two of which ( Nannolepidius Reichardt, 1932 and Toxometopon Reichardt, 1932 ) are monotypic and confined to the Afrotropical Region. Hypocacculus is absent in New World. This genus contains around 76 species worldwide (1 species is regarded incertae sedis) ( MAZUR 1997).

Discussion. As mentioned earlier, monophyly of this taxon is probably questionable (see Diagnosis of Axelinus or Chalcionellus ), with only a few weak supporting synapomorphies, most likely homoplasies. This is possibly a paraphyletic genus with several smaller genera deeply nested within Hypocacculus . The daunting task for the future researchers would be to revise this taxon and establish groupings of monophyletic taxa that it contains. This, however is a challenging task given the number of species that Hypocacculus contains, including many undescribed ones. The taxonomical value of its subgenera, artificial in authors’ opinion, must be likely tested using modern phylogenetic methods.