Liadytes aspidytoides, Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013

Prokin, Alexander A., Petrov, Pyotr N., Wang, Bo & Ponomarenko, Alexander G., 2013, New fossil taxa and notes on the Mesozoic evolution of Liadytidae and Dytiscidae (Coleoptera), Zootaxa 3666 (2), pp. 137-159 : 141

Liadytes aspidytoides sp. n.

Etymology: From the generic name Aspidytes ; adjective in the nominative singular.

Material: Holotype PIN 2470/942±, beetle without head, prothorax and legs; Shar Teg, Upper Jurassic, beds 441, layer 4; paratype 2470/945, less complete impression of beetle from the same locality, beds 451/3; additional specimen (cannot be identified with certainty, therefore not included in the type series) PIN 2470/938, isolated elytron from the same locality, beds 451/3.

Description ( Figs. 1–5 ): Beetle with dark elytra, which appear black due to carbonisation of organic substance in oxygen-free environment, and pale body. Maximum body width situated at level of elytral base. Mesocoxae only slightly separated, rounded. Maximum length of metaxocal plate (measured parallel to longitudinal body axis) 1.2 times as great as maximum length of lateral lobe of metaventrite (measured in same manner)3. Anterior margin of metacoxa weakly convex (metacoxal plate dilated anteriorly). Elevated median part of metacoxae with sides more or less straight, slightly diverging posteriad; metacoxal processes rounded posteriorly, with posterior margins meeting at an obtuse angle. Transverse suture of metaventrite present; median part of metacoxae elevated. Metepisternum 1.3 times as long as wide. Abdomen tapering from base of ventrite 4; ventrite 6 twice as long as ventrite 5. Elytron 3.4 times as long as wide. Epipleuron wide in its basal third, twice as wide as distally. Surface microsculpture of underside punctate, laterally on abdominal ventrites imbricate (according to Harris 1979).

Measurements: Body length, probably around 7 mm; body width, 3.1–3.7 mm; elytron length, 4.6–5.3 mm.

Comparison: The new species is similar to L. crassus Ponomarenko, 1977 in the convex anterior margins of the metacoxae (dilated anteriorly), but differs from it, as well as from the other species of Liadytes , in the presence of the elevated median part of the metacoxae (forming plates that partly cover the metafemora, as in Aspidytidae and Noteridae ; these structures are, apparently, derived from the broader femoral plates of the metacoxae4, homologous to those found in Haliplidae and many members of Geadephaga).

Notes: The shape of femoral plates of the metacoxae and broad epipleuron of the new species are similar to those of Aspidytes , but the new species differs from it and from Noteridae in the mesocoxae located close to each other and in the absence of the anteromedial metaventral process (see above). The metacoxal plates dilated anteriorly are characteristic of Aspidytidae and Liadytiscinae ( Dytiscidae ) (see next section), but the new species differs from representatives of Liadytiscinae in the presence of the transverse suture on the metaventrite. Therefore, the new species is included here in the genus Liadytes (Liadytidae) .

Figures

FIGURES 1 – 4. Liadytes aspidytoides sp. n.: (1) photo of holotype, (2) line drawing of holotype, (3) SEM photo of holotype, (4) SEM photo of details of metaventrite; arrows indicate metaventral suture.

FIGURES 5 – 7. (5) Liadytes aspidytoides sp. n., photo of specimen PIN 2470 / 945; Liadyxianus kirejtshuki sp. n.: (6) photo of holotype, (7) line drawing of holotype.