Cretoxenus, Fikáček & Prokin & Yan & Yue & Wang & Ren & Beattie, 2014
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publication ID |
https://doi.org/ 10.1111/zoj.12114 |
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persistent identifier |
https://treatment.plazi.org/id/03C287AC-FF8B-D67D-FEE4-BB4741F7987F |
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treatment provided by |
Marcus |
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scientific name |
Cretoxenus |
| status |
gen. nov. |
CRETOXENUS View in CoL GEN. NOV.
Type species: Cretoxenus australis sp. nov., by present designation.
Time range: Early Cretaceous.
Diagnosis: Body medium-sized, elongate oval; labrum exposed in front of clypeus ( Figs 3A, B View Figure 3 , 8C View Figure 8 ); anterior margin of clypeus concave ( Figs 3A, B View Figure 3 , 8C View Figure 8 ); maxillary palpi long ( Fig. 3A, B View Figure 3 ); prosternum moderately long ( Fig. 3A View Figure 3 ); procoxae contiguous; scutellar shield small, triangular; anapleural sutures of mesothorax well developed, nearly straight, converging anteriad ( Figs 3A View Figure 3 , 6I View Figure 6 , 8D View Figure 8 ); mesanespisterna narrowly separate by mesoventrite anteriorly ( Figs 3A View Figure 3 , 6I View Figure 6 , 8D View Figure 8 ); mesocoxal cavities very narrowly separated from each other; metaventrite prolonged into a triangular process posteriorly ( Figs 3A View Figure 3 , 6A View Figure 6 , 8D View Figure 8 ); metanepisternum rather narrow; elytron with punctate series ( Fig. 3A, B View Figure 3 ); sutural stria present, deeply impressed.
Etymology: The genus name consists of the prefix creto - referring to its Cretaceous age, and the ending - xenus indicating that the fossil is in some characters similar to the extant genus Limnoxenus . Masculine.
Family assignment: The combination of the antenna with antennal club, head not constricted behind eyes, presence of long maxillary palpi, small triangular scutellar shield, and femora with anteromesal corner not facing trochanter assign the fossil reliably to the family Hydrophilidae s.s. Additionally, it corresponds well with the modern Hydrophilidae in the general habitus and ventral morphology.
Comparison with other hydrophilid genera: By the combination of exposed labrum, medium body size, long maxillary palpi, mesoventrite well separates from mesanepisterna, and moderately long simple prosternum, Cretoxenus resembles the modern genera of the subfamilies Acidocerinae and Enochrinae , and of the tribe Hydrobiusini of the subfamily Hydrophilinae . It differs from the Enochrus clade of the Enochrinae by the nearly straight anapleural sutures (S-shaped in the Enochrus clade) and from the Cymbiodyta clade of the same subfamily by short mesotarsomere 1 (basal tarsomere is reduced in meso- and metathoracic legs in all representatives of the clade). The combination of the sutural stria, distinct elytral series of punctures, and long maxillary palpi distinguishes it from modern genera of the Acidocerinae . The non-denticulate lateral margins distinguish the fossil from the ‘sperchopsine’ genera of the Hydrobiusini . However, the posteriorly projecting mesal portion of the metaventrite corresponds with that present today in many Hydrobiusini (e.g. Limnoxenus Motschulsky, 1853 ; Fig. 6K, L View Figure 6 ), some of which ( Limnocyclus , Hybogralius Orchymont, 1942 ) even share with the fossil the nearly straight anapleural sutures of the mesothorax. The presence of long maxillary palpi and exposed clypeus also diagnoses the new genus from the Rygmodinae (which have concealed labrum and/or shorter and stouter maxillary palpi) many of which are otherwise also similar to the Hydrobiusini in general habitus. The fossil hence very likely belongs to the modern tribe Hydrobiusini of the subfamily Hydrophilinae ; the above characters as well as the age of the fossil justify its separate generic status.
For the diagnosis from the Late Jurassic Protochares gen. nov., see above under that genus. Cretoxenus differs from remaining two Early Cretaceous genera Alegorius gen. nov. and Hydroyixia gen. nov., by the combination of nearly straight anapleural sutures converging anteriad (subparallel anteriorly in Alegorius , converging but weakly angulate in Hydroyixia ), deeply arcuately excised anterior margin of clypeus (shallowly excised in Alegorius , with wide subtrapezoid excision in Hydroyixia ), and large exposed labrum (narrowly exposed in Alegorius , embedded in the clypeal excision in Hydroyixia ; see Table 2 and Fig. 8C, D View Figure 8 for details).
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