Chimaerocyon, Fikáček, Martin, Maruyama, Munetoshi, Vondráček, Dominik & Short, Andrew E. Z., 2013

Fikáček, Martin, Maruyama, Munetoshi, Vondráček, Dominik & Short, Andrew E. Z., 2013, Chimaerocyon gen. nov., a morphologically aberrant myrmecophilous genus of water scavenger beetle (Coleoptera: Hydrophilidae: Sphaeridiinae), Zootaxa 3716 (2), pp. 277-288 : 279-280

Chimaerocyon gen. nov.

( Figs. 1–30 )

Type species. Chimaerocyon shimadai sp. nov. (by present designation).

Diagnosis. Chimaerocyon largely resembles the representatives of the sphaeridiine tribes Omicrini (by the general thoracic and elytral morphology) and Coelostomatini (by the head and elytral morphology). Chimaerocyon gen. nov. is easily distinguishable from all known genera of Sphaeridiinae by the combination of the following characters: (1) elytral disc without striae or series of punctures including sutural stria, with remnants of 4–5 series preserved only subapically ( Figs. 1, 4 , 26–27 ; nearly unique within Hydrophilidae , only shared with Litrosurus ); (2) abdominal ventrite 5 with sexually dimorphic emargination ( Figs. 12–14 ; similar sexually dimorphic emargination only present in the genus Psalitrus ; a small emargination in some Coelostomatini is fringed by stout setae absent in Chimaerocyon and Psalitrus ). Additional characters distinguishing Chimaerocyon from part of sphaeridiine genera include: (1) male maxilla with sucking discs ( Figs. 6 , 16, 19 ; absent in all Hydrophilidae except Sphaeridiini and Megasternini ); (2) prothoracic hypomeron without antennal grooves ( Figs. 6 , 17 ; present in most Megasternini ); (3) prosternum extremely shortened in front of procoxae ( Figs. 6 , 17 ; not shortened in most Hydrophilidae except many Omicrini , Amphiopini and Berosini ); (4) mesothorax with mesoventrite fused with mesanepisterna, but without grooves for reception of procoxae ( Figs. 23–24 ; this combination is only present in Omicrini and some Coelostomatini ); (5) epipleuron wide throughout elytral length ( Figs. 6 , 23 ; absent in Megasternini and Sphaeridiini ); (6) median spur situated subapically of the M-Cu loop of hind wing ( Fig. 11 ; unique synapomorphy of the Megasternini ); (7) antennal club compact ( Figs. 16–17 ; loosely segmented in most Hydrophilidae except many Sphaeridiinae ). Detailed discussion of the assignment of Chimaerocyon gen. nov. to the Megasternini is provided in the discussion.

Description. Body widely oval to subtrapezoid, highly convex, Coloration reddish brown to black ( Figs. 1–5 ).

Head. Anterior margin of clypeus subangular, median portion rather narrow, anterolateral portion explanate, covering antennal bases ( Figs. 15, 18 ); marginal bead wide and distinct; frontoclypeal suture distinct laterally, reduced medially; transverse ridges absent. Median portion of frons and clypeus not elevated above remaining surface. Whole dorsal surface with fine and dense punctation, punctures lacking setae. Eyes small, situated on lateral angular portions of head, with dorsal portion smaller than ventral one, divided by 7.5–10× the width of one eye in dorsal view. Labrum ca. 0.4× as wide as head, membranous, largely retracted under anterior margin of clypeus, weakly bisinuate on anterior margin, densely pubescent dorsally ( Fig. 15 ). Maxilla of male with sucking disc on galea ( Figs. 16, 19 ); maxillary palpus with basal palpomere minute, palpomere 2 large, widened apically, ca. as long as palpomere 4, palpomere 3 ca. half as long as palpomere 4, slightly widening apicad, palpomere 4 cylindrical, without digitiform sensilla ( Fig. 16 ). Mentum ( Figs. 19, 22 ) transverse, ca. 2× wider than long, lateral margins without fringe of setae, anterior margin weakly bisinuate; premental lobes large, with long marginal setae; labial palps trimerous, basal palpomere very short, palpomeres 2 and 3 subequal in length, palpomere 2 with densely arranged setae. Antenna ( Fig. 16 ) with 9 antennomeres; scape long, cylindrical, curved basally; pedicel short, bulbous basally; antennomeres 3–5 short, subequal in length, slightly widening distad; cupule slightly asymmetrical, slightly larger than antennomere 5; antennomeres 6–9 forming an elongate pubescent club, antennomere 7 shortest, antennomeres 8–9 subequal in length, antennomere slightly constricted subapically, blunt at apex; special sensorial antennal fields absent. Submentum nearly bare, gular sutures vaguely developed, widely separated from each other, tentorial pits minute. Genal ridge long, arising from inner margin of eye and mesally reaching the level of maxillary cardo.

Prothorax. Pronotum transverse, highly convex, distinctly wider than bases of elytra combined; lateral margins narrowly beaded; punctation uniform, consisting of fine transverse punctures, punctures lacking setae except for those along lateral margins; series of larger punctures along posterior margin absent. Prosternum ( Figs. 6 , 17 ) narrow, as wide as ca. 0.3 of total width of prothorax, extremely short in front of procoxae; its median portion highly elevated into minute triangular plate ( Fig. 21 ). Hypomeron extremely large, divided into inner sparsely pubescent portion and wide lateral bare portion; antennal groove absent ( Fig. 17 ). Transverse fold behind posterior margin of pronotum absent. Profurca rather massive, with crescent-like apical portion ( Fig. 20 ). Procoxal cavities contiguous mesally, open medioposteriorly.

Mesothorax. Mesoventrite slightly longer than metaventrite, but inclined from the plane of metaventrite and hence appearing approximately as long as metaventrite ( Fig. 23 ). Mesoventrite with a low median carina projecting to a short rhomboid elevation posteriorly; grooves for reception of procoxae absent; anapleural sutures absent, mesoventrite fused with mesanepisterna ( Figs. 23–24 ). Mesepimeron very narrow, widening laterad. Mesocoxal cavities very narrowly separated. Mesofurca not examined. Scutellar shield in shape of small equilateral triangle ( Figs. 1, 4 ). Elytra ( Figs. 1, 4 , 26–27 ) narrowly to widely explanate laterally, punctural series absent on elytral disc as well as laterally, but distinctly developed, deeply impressed and hence forming a more or less deep depression mesally before elytral apex; epipleuron horizontal, very wide especially at junction of meso- and metathorax, gradually narrowing posteriad but still well developed at apex, indistinctly subdivided by a fine ridge into narrow lateral and wide mesal portions, its whole surface lacking pubescence.

Metathorax. Metaventrite only indistinctly elevated mesally, anteromesally projecting into narrow but rather long metaventral process ( Fig. 25 ), with a narrow bead behind mesocoxal cavities; femoral lines and anterolateral ridges absent. Metanepisternum ca. 5× as long as wide, without anterior oblique ridge, metepimeron with minute ventral portion. Metafurca not examined. Metathoracic wings ( Fig. 11 ) well developed, with transverse vein r4 arising from basal portion of radial cell, RP rather long, reaching ca. halfway to wing base, basal cubito-anal cell small, close, wedge cell absent, transverse vein mp-cua joining to MP3+4+CuA1+2; anal lobe not defined.

Legs generally rather short, with tips of femora not overlapping the outline of body ( Figs. 1, 4 , 6 ). Procoxae large, subglobular, slightly transverse, sparsely pubescent; meso- and metacoxae massive, transverse. Femora rather massive, with large tibial groove defined by high dorsal and ventral ridges ( Fig. 23 ), lacking pubescence; profemur without impressed parts; metafemur extremely enlarged in both sexes ( Fig. 23 ). Pro- and mesotibiae conical, with thin and short lateral spines and reduced mesal spines; metatibiae slightly depressed. Tarsi pentamerous, with extremely shortened but wide tarsomeres ( Fig. 28 ), each tarsomere with tuft of stiff setae ventrally and a few fine setae dorsally; metatarsomere 1 slightly longer than tarsomere 2, tarsomeres 2–4 subequal in length, tarsomere 5 longest. Claws simple, arcuate; empodium bisetose ( Fig. 29 ).

Abdomen with five ventrites. Ventrite 1 with low mesal carina developed only basally, hence seemingly ecarinate ( Fig. 6 ). Ventrites 2–5 ecarinate mesally. Apical portion of ventrite 5 narrowly emarginate in both sexes, shape of the emargination species-specific and sexually dimorphic ( Figs. 12–14 ). Male sternite 8 crescent-like ( Fig. 9 ), without median narrow projection on anterior margin, with two rows of setae on posterior margin not meeting mesally. Male sternite 9 tongue-like mesally ( Fig. 10 ). Aedeagus ( Fig. 8 ) simple, median lobe with complex basal hooks, not protruding into phallobase, phallobase short, strongly asymmetrical; parameres simple. Female genitalia corresponding with those of Kanala .

Etymology. The generic name is derived from chimaera (Greek, mythical animal with body parts taken from various animals) which reflects the fact that the genus combines the diagnostic characters of several sphaeridiine tribes, and the suffix -cyon, a typical suffix of generic names within the tribe Megasternini to which the new genus belongs. The new generic name is masculine.

Figures

FIGURES 1 – 5. Habitus of Chimaerocyon species. 1 – 3 — male paratype of Chimaerocyon shimadai (1 — dorsal view, 2 — lateral view, 3 — frontal view). 4 – 5 — holotype of C. sumatranus (4 — dorsal view, 5 — frontal view).

FIGURES 6 – 14. Morphological details of Chimaerocyon shimadai (6 – 13) and C. sumatranus (14). 6 — ventral view, 7 — egg drawn to scale with Fig. 6, 8 — aedeagus of the holotype, 9 — male sternite 8 of the holotype, 10 — male sternite 9, 11 — hind wing of the holotype, 12 – 14 — abdominal apex (12 — male holotype of C. shimadai, 13 — female paratype of C. shimadai, 14 — female holotype of C. sumatranus). Abbreviations (numbers refer to characters in Fig. 32): msuc — male suckers on maxilla, elpr — elevated median portion of prosternum, wepi — wide epipleuron posteriorly, shtars — shortened tarsus, abdem — abdominal emargination.

FIGURES 15 – 22. Detailed morphology of Chimaerocyon shimadai (15 – 21) and C. sumatranus (22). 15 — head in dorsal view, 16 — head in ventral view, 17 — prothorax and head in ventral view, 18 — clypeus in lateral view, 19, 22 — mentum, 20 — profurca, 21 — elevated mesal portion of prosternum. Abbreviations (numbers refer to those used in Fig. 32): cly — clypeus, msuc — male sucker on maxilla.

FIGURES 23 – 30. Detailed morphology of Chimaerocyon shimadai (23 – 26, 28 – 30) and C. sumatranus (27). 23 — meso- and metathorax in ventral view, 24 — mesoventrite in lateral view, 26 — median portions of meso- and metaventrite in ventral view, 26 – 27 — right elytral apex, 28 — metatarsus, 29 — metatarsal claws, 30 — detail of apical portion of elytral series 1 – 2.