Helophorus (Mesosperchus) tarsalis (Ponomarenko, 1977) Fikáček & Prokin & Angus & Pono & Marenko & Yue & Ren & Prokop, 2012

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 : 104-105

† Helophorus (Mesosperchus) tarsalis (Ponomarenko, 1977) comb. nov.

( Figs. 29–37 , 73–79 , 83–84)

Mesosperchus tarsalis Ponomarenko, 1977b: 109 . Mesohelophorus elongatus Ponomarenko, 1990: 48 , syn. nov.

Type locality and age (both for Mesosperchus tarsalis and Mesohelophorus elongatus ). Russia, Zabaykalskiy Kray, Baley district, right bank of the Unda river 2 km upstream of the Zhidka village (outcrops Unda and Daya), Glushkovo Formation, Latest Jurassic, Tithonian, ca. 151–146 mya ( RASNITSYN 1990, SINITSHENKOVA & ZHERIKHIN 1996; Vasilenko, pers. comm. to A. Prokin, 2011).

Material examined (8 spec.). Mesosperchus tarsalis : HOLOTYPE: PIN 3015/367 (piece and counterpiece). PARATYPE: PIN 3063/116 (piece and counterpiece). Mesohelophorus elongatus : HOLOTYPE: PIN 3063/735 (piece and counterpiece). ADDITIONAL NON- TYPE SPECIMENS: PIN 3063/2192 (Daya, piece and counterpiece), PIN 3063/2194 (Daya, piece and counterpiece), PIN 3015/1769 (Unda, piece and counterpiece), PIN 3063/2195 (Daya, piece and counterpiece), PIN 3063/2197 (Daya, piece and counterpiece).

Redescription. Adult: Body elongate oval, 3.1–3.7 mm long (holotype ca. 3.2 mm). Head with very distinct frontoclypeal suture, its median portion grooved; both frons and clypeus bearing distinct granulation; eyes protruding laterad, narrow postocular bridge present. Mentum narrow, ca. 1.3× wider than long; gula wide. Maxillary palpi long, palpomere 4 most probably asymmetrical. Pronotum transverse, bearing five longitudinal grooves, pronotal intervals with sparse but distinct granulation; prosternum long anterior to procoxae, antennal groove present; pronotal flank narrow. Mesoventrite narrowing anteriad, with distinct transverse ridge posteromedially. Metaventrite twice as long as mesoventrite, metepimera rather wide, with oblique transverse ridge anteriorly. Elytron with finely punctate and impressed striae, scutellar stria absent. Legs rather long, tibiae with several longitudinal series of fine spines, bearing larger spines on distal apices; tarsi slightly shorter than tibiae, basal tarsomere very short, tarsomere 2 longer than tarsomere 3; swimming hairs absent or not preserved both on tibiae and tarsi. Abdomen with five ventrites. Aedeagus rather short and wide, phallobase symmetrical with basal manubrium, ca. twice as long as parameres, parameres slightly arcuate, gradually narrowing from base to apex, median lobe widely rounded apically, with basal struts ca. twice as long as its distal portion.

Taxonomic notes. Two species were originally described from the outcrops of Unda and Daya, both belonging to the Glushkovo Formation and situated closely apart: Mesosperchus tarsalis defined by its widely oval body, short and thick tarsi and the absence of pronotal grooves (hence its assignment to Mesosperchus ; PONOMARENKO 1977b), and Mesohelophorus elongatus defined by its narrowly elongate body, long and slender tarsi and a pronotum with longitudinal furrows (hence its assignment to Mesohelophorus ; PONOMARENKO 1990). The reexamination of the type and additional material from the Unda and Daya outcrops revealed that both taxa are actually extremely similar in all preserved characters and we failed to find any character other than the body proportions which would distinguish both species from each other. Body proportions seem to vary considerably among the examined specimens and the extremely elongate form of the holotype of Mesohelophorus elongatus seems be caused by deformation during the fossilization process (much in the way present also in Laetopsia mongolica and discussed above). The difference in the presence / absence of pronotal grooves seems to be artificial as well, caused by generally bad preservation of the prothorax in the type specimens of Mesosperchus tarsalis . For all these reasons as well as due to the high proximity of both outcrops, both forms seem to be conspecific and we therefore consider Mesohelophorus elongatus as a junior subjective synonym of Helophorus (Mesosperchus) tarsalis .

Figures

Figs. 29–37. Helophorus (Mesosperchus) tarsalis (Ponomarenko, 1977). 29–30 – PIN 3063/2194, piece and counterpiece; 31–32 – PIN 3063/2192 (31 – general view of the piece, 32 – detail of genitalia of the counterpiece); 33–34 – PIN 3063/735, holotype of Mesohelophorus elongatus Ponomarenko, 1990, piece and counterpiece; 35 – PIN 3063/116; 36 – PIN 3015/367, holotype of Mesosperchus tarsalis Ponomarenko, 1977; 37 – PIN 3015/1769. Scale bars: 1 mm. Abbreviations: aed – aedeagus; mxp – maxillary palpus; sct – scutellum.

Figs. 73–82. Representatives of Helophorus, subgenus Mesosperchus Ponomarenko, 1977. 73–79 – Helophorus tarsalis (Ponomarenko, 1977) (73 – PIN 3063/116, paratype; 74 – PIN 3063/2192, piece, general view; 75 – PIN 3015/1769; 76 – PIN 3063/2192, counterpiece, detail of male genitalia; 77– PIN 3063/2194. piece under alcohol; 78 – same specimen, counterpiece in dry condition; 79 – PIN 3015/367, holotype). 80 – Helophorus gracilis (Prokin, Ren & Fikáček, 2010), CNU 2010018, holotype. 81–82 – Helophorus inceptivus, PIN 4270/1008 (81 –detail of head and pronotum; 82 – general view). Scale bars: 1 mm (Figs. 73–80, 82); 0.5 mm (Fig. 81).