Hydroyixia elongata, Fikáček & Prokin & Yan & Yue & Wang & Ren & Beattie, 2014

Fikáček, Martin, Prokin, Alexander, Yan, Evgeny, Yue, Yanli, Wang, Bo, Ren, Dong & Beattie, Robert, 2014, Modern hydrophilid clades present and widespread in the Late Jurassic and Early Cretaceous (Coleoptera: Hydrophiloidea: Hydrophilidae), Zoological Journal of the Linnean Society 170 (4), pp. 710-734 : 726-727

HYDROYIXIA ELONGATA SP. NOV.

Type locality and age: China, Liaoning Province, Shangyuan County, Chaomidian Village, Huangbanjigou, Yixian Formation, Early Cretaceous, Lower Cretaceous, Aptian, 124.6 Mya ( Swisher et al., 1999). An alternative dating was proposed by Zheng et al. (2003): Jurassic–Cretaceous boundary, Late Tithonian to Berriasian, c. 145–140 Mya. See Ren et al. (2010) for discussion on various datings of the formation.

Material examined (two specimens): Holotype: CNU 2010005 , piece and counterpiece ( Figs 5A, B , 7H–L ) . Paratype: CNU 2009075 , piece only ( Figs 5C–E , 7F–G ) .

Description (characters seen only in the paratype marked by an asterisk).

Body narrowly elongate. For body measurements see Table 1.

Head. Clypeus large, slightly expanding laterally; frontoclypeal sutures very distinct, reaching lateral margin of head closely before eyes; anterior margin widely excised, excision angular laterally; dorsal surface finely and densely punctated*. Eyes rather large, separated by 2.3–2.6× the width of one eye. Labrum transverse, partly exposed anterior to clypeus, slightly narrowing posteriad*, weakly convex on anterior margin. Gula narrowing anteriad, with longitudinal ridge mesally, gular sutures widely separated. Mentum large, subrectangular, c. 2.0× wider than long.

Prothorax. Pronotum transverse, slightly narrowing anteriad, anterolateral corners slightly projecting anteriad; lateral margin arcuate, with a narrow bead; lateral portions with a group or trichobothria much larger than ground punctation*. Prosternal process wide and short, procoxae contiguous.

Mesothorax. Mesoventrite subtriangular, extremely narrow at anterior margin; mesal portion probably with an elevated carina. Anapleural sutures well developed, slightly curved, converging anteriad, joint at anterior margin of mesoventrite. Mesepimeron subtriangular. Mesocoxae only narrowly separated. Elytra combined nearly parallel-sided, each elytron with sharply impressed sutural stria reaching c. elytral midlength; elytra with finely punctate elytral series*, serial punctures only slightly larger than interval punctation*, alternate elytral intervals with large and very conspicuous trichobothria; epipleuron well developed anteriorly, rather wide, subdivided into outer and inner portion.

Metathorax. Metaventrite c. as long as mesoventrite, probably at least slightly elevated mesally, narrowly projecting between mesocoxae anteriorly; only slightly projecting posteriad. Anepisternum 3.1× as long as wide.

Abdomen with five ventrites, ventrite 1 probably weakly carinate anteriorly, without carina in posterior portion. Ventrite 5 with shallow wide apical emargination.

Differential diagnosis: Hydroyixia elongata sp. nov. differs from the following species especially in the narrowly elongate body shape (widely elongate in H. latissima ), parallel-sided elytra (widest anteriorly and narrowing posteriad in H. latissima ), distinctly larger mentum (small in H. latissima ) and metaventrite c. as long as mesoventrite (much longer than mesoventrite in H. latissima ).

Etymology: The species name refers to the elongate body shape of this species.

Comments: The paratype of H. elongata differs from the holotype by rather significantly larger body size (body length 11.8 mm compared with 8.3 mm of the holotype), which may indicate it is in fact not conspecific with the holotype. Still, both specimens correspond well in body proportions and the size of the mentum considered by us as diagnostic characters, and the variation of the body size (35%) is still in the range observed in variable species of the extant Acidocerinae . Unfortunately, the ventral characters are not preserved in the paratype, and its wellpreserved characters of the dorsal surface (e.g. trichobothria) cannot be compared with the holotype in which the dorsal portion is rather poorly preserved. We hence tentatively consider both specimens as representing a single species.

Figures

Figure 5. Well-preserved specimens of Hydroyixia gen. nov., Yixian Formation, China. Hydroyixia elongata sp. nov.: holotype CNU 2010005, piece and counterpiece (A, B); paratype CNU 2009075, whole specimen (C), detail of head and pronotum (D); detail of elytral apices (E). Hydroyixia latissima sp. nov.: holotype, CNU 2009074, whole specimen (F), detail of abdominal apex (G); posterior leg of paratype CNU 2010014 (H); paratype CNU 2009107 (I). Abbreviations: abem, apical emargination of abdominal ventrite 5; aes3, metanepisternum; apls, anapleural sutures; cl, clypeus; fcs, frontoclypeal suture; gs, gular suture; lb, labrum; men, mentum; msv, mesoventrite; mtv, metaventrite; mttr1, metatarsomere 1; pros, prosternum; sstr, sutural stria; trich, trichobothrium.

Figure 7. Hydrophilid fossils from Early Cretaceous Yixian Formation, China. Alegorius yixianus sp. nov.: holotype CNU 2009079, whole specimen (A), detail of meso- and metaventrite (B), detail of abdominal apex (C); paratype CNU 2009078, whole specimen (D), detail of mesoventrite (E). Hydroyixia elongata sp. nov.: paratype CNU 2009075, detail of head and pronotum (F), whole specimen (G); holotype CNU 2010005: whole beetle, piece and counterpiece (H, I), detail of head (J), detail of meso- and metaventrite (K), detail of abdominal apex (L). Hydroyixia latissima sp. nov.: holotype CNU 2009074, detail of abdominal apex (M), whole specimen in dry condition (N) and under alcohol (O). Abbreviations: apls, anapleural suture; abem, apical emargination of abdominal ventrite 5.