Mesosperchus Ponomarenko, 1977

Fikáček, Martin, Prokin, Alexander, Angus, Robert B., Pono, Alexander, Marenko, Yue, Yanli, Ren, Dong & Prokop, Jakub, 2012, Revision of Mesozoic fossils of the helophorid lineage of the superfamily Hydrophiloidea (Coleoptera: Polyphaga), Acta Entomologica Musei Nationalis Pragae 52 (1), pp. 89-127 : 103-104

Subgenus † Mesosperchus Ponomarenko, 1977 stat. nov.

Mesosperchus Ponomarenko, 1977b: 108 . Mesospercheus (incorrect subsequent spelling): ARNOLDI et al. (1992: 148, name changed by translators).

Type species. Mesosperchus tarsalis Ponomarenko, 1977 (by original designation).

Time range. Late Jurassic (ca. 150–146 mya) to Jurassic–Cretaceous boundary (ca. 145–140 mya).

Diagnosis. Adult: Head and pronotum with setiferous granules; frontoclypeal suture very distinct, its median portion grooved; gula moderately wide, with well-separated gular sutures; pronotum with five longitudinal grooves; pronotal flanks narrow; elytra with sutural stria; all elytral intervals flat, alternate ones never elevated, costate or bearing tubercles.

Taxonomic notes. The subgenus Mesosperchus is understood here as a paraphyletic formal taxon defined solely by the absence of the apomorphies of any other subgenus of Helophorus (hence, it is defined by plesiomorphies only). It is designed to accommodate fossil species which can be clearly assigned to the genus Helophorus , but lack any characters allowing further subgeneric assignment. As such, Mesosperchus may be understood as a formal taxon containing Late-Jurassic stem taxa of the genus Helophorus . We are, however, unable to distinguish between fossil species in which additional apomorphies have been really absent from those in which they are only not preserved. Hence, Mesosperchus may also contain species representing extinct basal lineages of Helophorus (rather than stem taxa) or even species which would be classified as a part of an other subgenus recognized at present if their preservation was better.

PONOMARENKO (1992) synonymised Mesosperchus with the genus Zetemenos Bode, 1953 , previously containing a single species, Z. sexlineatus Bode, 1953 . The re-examination of the holotype of this species (see below for details) showed that the specimen is very poorly preserved and does not bear any synapomorphy indicating its assignment to the Helophoridae or Hydrophiloidea . For that reason, the synonymy of Mesosperchus with Zetemenos is rejected here and Mesosperchus is re-established as a valid taxon.

Taxa excluded from Mesosperchus . Mesosperchus angulatus Ponomarenko, 1985 , M. notatus Ponomarenko, 1977 and M. schultzi Ponomarenko, 1985 (for details see under Taxa excluded from the Hydrophiloidea ).