Bezesporum huchengi, Li & Huang & Cai, 2024

Li, Yan-Da, Huang, Di-Ying & Cai, Chen-Yang, 2024, A new species of Bezesporum from mid-Cretaceous Kachin amber (Coleoptera: Myxophaga: Sphaeriusidae), Zootaxa 5538 (3), pp. 293-296 : 293-295

Bezesporum huchengi sp. nov.

( Figs 1–2 )

Material. Holotype, NIGP204941 .

Etymology. The species is named after Mr. Cheng Hu, who kindly donated many fossils for our research.

Locality and horizon. Amber mine located near Noije Bum Village, Tanai Township, Myitkyina District, Kachin State, Myanmar; unnamed horizon, mid-Cretaceous, Upper Albian to Lower Cenomanian.

Diagnosis. The new species differs from other extant and extinct species of Bezesporum by the more elongate antennomere 6 ( Fig. 2C ). The biemarginate abdominal apex may also be a distinctive feature of the new species ( Figs 1B , 2B ). To our knowledge, this feature has not been reported in any other sphaeriusids, although the state of abdominal apex was not explicitly described or illustrated in many cases.

Description. Body broadly oval, strongly convex, about 0.78 mm long, 0.52 mm wide.

Head prognathous, short and broad. Antennae 11-segmented, with 4-segmented club; antennomeres 1 and 2 robust; antennomere 3 strongly elongate (more than three times as long as 4); antennomeres 4, 5 and 7 submoniliform; antennomere 6 elongate; antennomeres 8–11 forming elongate club, with distinct setae. Clypeus converging anteriad. Mandibles small, obliquely bidentate. Maxillary palps probably 4-segmented; apical palpomere distinctly shortened.

Pronotal disc convex, widest at hind angles. Scutellar shield small, triangular, posteriorly acute. Elytra complete, covering all abdominal segments. Hind wing with long fringe hairs. Prosternum subtriangular, narrowing posteriad. Mesoventrite relatively long, on the same plane with metaventrite, fused with the latter. Mesocoxae widely separated. Metaventrite broad, transverse. Metacoxae contiguous, extending laterally to elytra; metacoxal plates gradually narrowed laterally in outer half. Legs short. Mesotrochanter fused with femur; anterior margin of mesotrochanterofemur sinuate. Tibiae and tarsi setose; metatarsus with very long setae. Pretarsal claws simple, unequal.

Abdomen with apex biemarginate.

Remarks. Fikáček et al. (2023) proposed a series of characters to define Bezesporum . Among these, the 4-segmented antennal club and T-shaped prosternum may be found in some extant Sphaerius ( Kamezawa & Matsubara, 2012; Fikáček et al., 2023), and the sinuate anterior margin of mesotrochanterofemur and the presence of long setae on metatarsus are known in the fossil S. martini ( Li et al., 2023) . Nevertheless, the anteriad converging clypeus and relatively long mesoventrite are, to date, exclusively known in Bezesporum . The new species exhibits a 4-segmented antennal club, a T-shaped prosternum, a sinuate anterior margin of mesotrochanterofemur, long setae on metatarsus, and particularly, an anteriad converging clypeus and a relatively long mesoventrite. Therefore, the new species fits perfectly within the genus Bezesporum .

The elongate antennomere 6 is diagnostic of the new species. According to the drawing by Fikáček et al. (2023), the antennomere 6 of the fossil B. burmiticum is not clearly longer than the antennomere 5. In extant B. minutum (Liang & Jia), the antennomere 6 is no longer than 1.4× the length of antennomere 5 ( Liang & Jia, 2018: fig. 8). By contrast, the antennomere 6 of B. huchengi sp. nov. is relatively elongate, being 1.7–1.9× as long as antennomere 5 (based on measurements from both antennae) ( Fig. 2C ). The relative length of antennomere 6 of the extant species B. papulosum (Lesne) was not explicitly described by Lesne (1940), but since Liang & Jia (2018) stated B. papulosum closely resembles B. minutum, it might also have a relatively short antennomere 6. Besides, Lesne (1940) reported that antennomere 3 in B. papulosum is much longer than antennomeres 4–8 combined (possibly also implying a short antennomere 6), whereas the antennomere 3 is clearly shorter than antennomeres 4–8 combined in B. huchengi . Our discovery of a new species from the Kachin amber underscores the rich paleodiversity of Sphaeriusidae in the late Mesozoic.

Figures

FIGURE 1. General habitus of Bezesporum huchengi sp. nov., holotype, NIGP204941, under incident light. A, Dorsal view. B, Ventral view. Scale bars: 200 μm.

FIGURE 2. Bezesporum huchengi sp. nov., holotype, NIGP204941, under confocal microscopy. A, Habitus, dorsal view. B, Habitus, ventral view. C, Head and prothorax, ventral view. D, Hind leg, with arrow indicating long setae on metatarsus. Abbreviations:a5–11, antennomeres 5–11; cl, clypeus; msv, mesoventrite; mtts, metatarsus; mxp, maxillary palp; ps, prosternum. Scale bars: 100 mm.