Basinosa Tihelka, Huang & Cai, 2020

Li, Yan-Da, Tihelka, Erik, Dahan, Loïc, Huang, Di-Ying & Cai, Chen-Yang, 2021, On the Nosodendridae from mid-Cretaceous amber of northern Myanmar (Coleoptera: Nosodendroidea), Zootaxa 5082 (3), pp. 223-244 : 236-237

Genus Basinosa Tihelka, Huang & Cai, 2020

( Figs 15 , 16 )

Type species. Basinosa pengweii Tihelka, Huang & Cai, 2020 .

Material examined. Holotype of B. pengweii, NIGP 173119.

Remarks. The amber piece containing the holotype of B. pengweii is somewhat nontransparent, making it difficult to determine many of the characters using normal optical methods. Partly due to tomographic artefacts, some characters were not clearly visualized in previous micro-CT reconstructions. For example, one of the key diagnostic characters for Nosodendridae , the 11-segmented antenna with 3-segmented club, could not be observed in Tihelka et al. (2021a), although other diagnostic characters could be confirmed.

Here we reexamine the original CT data for the holotype of B. pengweii . It turns out that the majority of the beetle body has high absorption (white), while the antennae (especially the left one) appear to have lower absorption (black) ( Fig. 16A ). Therefore, the antennae were not properly reconstructed in the simple reconstruction, where only regions with a density higher than a selected threshold were extracted. Confocal microscopy confirms the 3-segmented club of B. pengweii ( Fig. 16C ). Since the strong laser could penetrate the somewhat opaque amber matrix better, and out-of-focus light is blocked, the confocal microscope could image this material much better than widefield ones ( Fu et al. 2021). The medial antennomeres of B. pengweii appears to be relative elongate ( Fig. 16B ), while in extant Nosodendron the medial antennomeres are almost as long as wide. Confocal microscopy additionally reveals that the prosternal process ( Fig. 16E ) is not as slender as shown in the CT reconstruction by Tihelka et al. (2021a), which was subsequently adopted as one of the characters differentiating Basinosa from Mesonosa (Tihelka et al. 2020b) . Detecting the boundaries of structures under CT is a challenging task ( Coleman & Colbert 2007); the boundaries between the beetle and the amber matrix are not clearly defined, but are instead represented by a continuum of transitional values. Thus, a different selection of the threshold value for extraction could sometimes greatly affect the visual appearance.

The 3-segmented antennal club, together with the previously shown subantennal groove, wide metaventrite, clearly delimited anterolateral depression of metaventrite for the reception of mesotibial apex and basal mesotarsomeres, and narrowly separated metacoxae (all present in extant Nosodendridae and fossil Nosodendridae from the Burmese amber; fig. 23C in Ge et al. 2007), further confirm the placement of Basinosa in Nosodendridae . Basinosa is unique in Nosodendridae in having a relatively large body and complete antennal grooves on prosternum.

Figures

FIGURE 15. General habitus of Basinosa pengweii Tihelka et al., holotype, NIGP173119, under incident light. A, Dorsal view. B, Ventral view. Scale bars: 5 mm.

FIGURE 16. Details of Basinosa pengweii Tihelka et al., holotype, NIGP173119. A, Weighted average stacking of micro-CT slices, showing the left antenna and antennal groove on head. B–F, confocal images. B, C, Antenna, ventral view. D, Mandibles, dorsal view. E, Prosternal process, ventral view. F, Metatarsus.Abbreviations: ag, antennal groove; an, antenna; an3–11, antennomeres 3–11; md, mandible; mtt1–4, metatarsomeres 1–4; mttb, metatibia; ps, prosternum. Scale bars: 1500 μm in A, 400 μm in B–F.