Hypocaccus C. Thomson, 1867

Lackner, Tomáš, 2010, Review of the Palaearctic genera of Saprininae (Coleoptera: Histeridae), Acta Entomologica Musei Nationalis Pragae (suppl.) 50, pp. 1-254 : 139-140

Hypocaccus C. Thomson, 1867

Hypocaccus C. Thomson, 1867: 400 . Type species: Hister quadristriatus Hoffmann, 1803 , designated by LEWIS (1899): 3.

Hypocaccus: SCHMIDT (1885a) : 302; GANGLBAUER (1899): 382; LEWIS (1899): 3; REITTER (1909): 291; BICKHARDT (1916 –1917): 82, 98; REICHARDT (1926): 14; REICHARDT (1941): 156, 305; PEYERIMHOFF (1936): 226; MCGRATH & HATCH (1941): 54; BLACKWELDER & BLACKWELDER (1948): 11; WENZEL (1962): 374, 380; HATCH (1962): 257; HALSTEAD (1963): 9; DAHLGREN (1969): 64–66; WITZGALL (1971): 173; MAZUR (1973): 38; KRYZHANOVSKIJ & REICHARDT (1976): 112, 217; MAZUR & KASZAB (1980): 7, 57; VIENNA (1980): 116, 182; MAZUR (1981a): 72, 99; MAZUR (1984): 92; ÔHARA (1994): 215, 243; DOWNIE & ARNETT (1996): 607, 610; KIM & LIM (1997): 60; MAZUR (1997): 257; ÔHARA & PAIK (1998): 28; BOUSQUET & LAPLANTE (1999): 141, 164; MAZUR (2001): 19, 33; KOVARIK & CATERINO (2001): 220, 223; YÉLAMOS (2002): 245, 326; MAZUR (2004): 94; BOUSQUET & LAPLANTE (2006): 168, 169.

Rhytidoprinus Houlbert & Monnot, 1923: 46 Type species: Hister rugiceps Duftschmid, 1805 , designated by MAZUR (2004): 94. Synonymized by COOMAN (1947): 428.

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Diagnosis. Cuticle often metallic and lustrous, at times matt, black or dark-brown; frontal stria carinate, in most cases straight or only slightly curved outwardly (rarely weakened medially with traces prolonged onto clypeus); frontal disc marked by single or double chevron, sometimes with longitudinal rugae or granulose structures. Pronotal disc punctate (at times rugulose-lacunose) or entirely smooth (subgenus Baeckmanniolus ), pronotal foveae absent, pronotal hypomeron glabrous. Prosternal process concave, compressed, carinal prosternal striae usually running parallel or subparallel, occasionally united in front; lateral prosternal striae united anteriorly under a sharp angle; pre-apical foveae present, usually moderately sized. Lateral sides of meso- and metaventrites occasionally shortly setose, often smooth. Outer margin of metatibia with two (subgenus Hypocaccus ) or three (subgenus Baeckmanniolus ) rows of short denticles.

Differential diagnosis. Representatives of this genus are most similar to the genus Exaesiopus , differing from it by the glabrous pronotal hypomeron (setose in Exaesiopus ) as well as not particularly thickened metafemora (strongly thickened in Exaesiopus ). The species Hypocaccus (Hypocaccus) crassipes ( Erichson, 1834) which has slightly thickened metafemora, but a glabrous pronotal hypomeron, is probably externally most similar to the species of the genus Exaesiopus . This species has been previously transferred between genera Exaesiopus and Hypocaccus , but can be viewed as a transitional form between them ( KRYZHANOVSKIJ & REICHARDT 1976: 228). Several smaller species of the subgenus Hypocaccus are externally very similar to the species of the subgenus Nessus of genus Hypocacculus and according to MAZUR (pers. comm. 2008), Nessus ought to be synonymized with Hypocaccus (see also above).

Biology. Species of the subgenus Hypocaccus are found on the sandy shores of seas, lakes and rivers (sometimes also on inland sand dunes without the presence of water) where they prey upon dipteran larvae developing in various decomposing organic substances such as excrements, carcasses, seaweed, etc. Species of the subgenus Baeckmanniolus are confined to seashores with similar feeding habits.

Distribution. Hypocaccus , with around 65 described species and subspecies is a worldwidedistributed genus, with the bulk of its species known to occur in the Holarctic Region ( MAZUR 1997). Several species (e.g. Hypocaccus (Hypocaccus) brasiliensis ) are widely distributed on the beaches around the globe; others (e.g. Hypocaccus (Hypocaccus) ainu Lewis, 1899 from Japan) are confined to mountain rivers and streams of geographically limited regions.

Discussion. Hypocaccus is probably a paraphyletic taxon with respect to several smaller genera e.g. Exaesiopus , or subgenus Nessus of the genus Hypocacculus (see above). It is supported only by several weak synapomorphies that include frontal disc with chevrons, longitudinal rugae or granulose structures. Subgenus Baeckmanniolus is supported by only two weak putative synapomorphies, most likely homoplasies. Revision of the members of both subgenera of Hypocaccus would be one of highly required tasks for the future research.