Tigrivia baii Bao et al., 2023

Bao, Liang, Beutel, Rolf Georg, Niu, Kecheng & Bao, Tong, 2025, Redescription of the highly specialized aquatic † Tigrivia and the classification of the Mesozoic † Coptoclavidae (Coleoptera, Adephaga, Dytiscoidea), Zootaxa 5588 (3), pp. 401-425 : 403-407

† Tigrivia baii Bao et al., 2023

urn:lsid:zoobank.org:act:19BDD6A1-C747-4995-8526-CC3F6751B1F1

Etymology. The name paid homage to Bai, a fossil collector ( Bao et al. 2023).

Diagnosis. as for genus.

Type material used here and in the original description. Holotype: YLSNHM01120 / Tigrivia baii; adult, female (visible female gonocoxosterna), well preserved specimen .

Type stratum and type locality. Impression fossil.

Type stratum and type locality. Impression fossil. Jiufotang Formation , Early Cretaceous ( Chang et al. 2009) , Daobaliang mountain, Weichang County, Hebei Province, China.

Redescription ( Figs 1–3 ). Body oval, posteriorly widening. Length 30 mm; maximum width ca. 12.5 mm; ratio of length to maximum width 2.38. Elytra posteriorly truncated, leaving posterior abdominal structures exposed.

Head prognathous, widening posteriorly, strongly retracted into prothorax, especially dorsally. Length of exposed part 3.7 mm, maximum width 4 mm. Laterally placed compound eyes large, round, diameter ca. 2.4 mm, slightly protruding; dorsally and ventrally visible portions of about equal size, not separated by a chitinous bridge, compound eyes thus undivided; hind margin almost adjacent with anterior pronotal margin. Labrum transverse, anterolaterally rounded, medially with shallow, rounded emargination (visible in ventral view). Antennae not recognizable. Mandibles comparatively short and robust, partly exposed, distally slightly curved inwards. Maxillae not clearly recognizable; maxillary palps not visible. Labium with distinct, rounded lateral lobes of mentum enclosing large prementum, labial palps not recognizable. Gula delimited by distinct gular ridges (visible on right side).

Prothorax small in relation, to pterothoracic segments. Pronotum trapezoid, with anteriorly converging, very slightly convex lateral edges; length 4.3 mm, width of anterior margin 5.3 mm, width of posterior margin 6.3 mm; anterior pronotal margin very slightly concave, slightly wider than occipital region of head, distinctly overlapping with it; posterior margin distinctly protruding between elytral bases, rounded posteromedially. Prosternum very short, transverse; length 1.0 mm, width 3.0 mm.Prosternal process almost completely reduced, present only as small triangle projecting slightly between procoxae. Sternopleural suture not visible. Propleura large, slightly widening laterally; suture separating it from pronotal hypomeron not visible; protrochantin also not recognizable. Mesoscutellar shield small but distinctly visible, triangular. Ventral side of thorax strongly disrupted between procoxae and mesoventrite; mesonotum visible in wide gap as exposed skeletal element, with anteromedian prominence with two rounded tips separated by round median incision, pair of distinct lateral processes, and quadrangular posterior part, separated from remaining structure by distinct transverse line. Mesoventrite visible as well-developed transverse and largely flat plate-like sclerite anterior to large mesocoxae; length 3.0 mm, width 7.0 mm; hexagonal groove for reception of prosternal process absent; long median discrimen apparently present, visible as deep median impression; transverse anterolateral delimited areas of mesoventrite distinct, probably concave and functioning as procoxal and protrochanteral rests. Mesopleuron laterally adjacent with mesoventrite; anepisternum roughly triangular; pleural suture recognizable as faintly impressed line; posterior border of mesepimeron only partly visible. Metathorax distinctly larger than mesothorax. Metaventrite short and wide, 3.4 times as wide as long, but not reaching elytral epipleura and anterolateral metacoxal edge laterally; rounded anteromedian process between posterior mesocoxal margins present but short; discrimen of metaventrite largely absent or not recognizable externally, only visible on katepisternal region anterior to metacoxae. Very short katepisternum delimited by faintly visible transverse suture, ending at about 1/3 of metacoxal width. Metanepisternum elongate, fairly narrow, widening anteriorly; metepimeron not visible.

Tarsal formula 5–5–5 ( Figs 2 , 3A ). Forelegs strongly elongated, raptorial. Procoxa moderately sized, wider than long; rounded anteriorly, laterally, and posterolaterally, but with straight, medially adjacent mesal margins. Protrochanter distinctly smaller than meso- and metathoracic equivalents. Profemur elongated, 5.9 mm long, very slightly widening distally. Protibia elongated and slender, slightly narrowed in middle region, 5.8 mm long; with single strongly developed mesal spur on apex. Protarsus elongate; length formula 1.1–1.4–0.75–0.5–1.4 mm; protarsomere 1 moderately widening distally, likely equipped with curved spur (visible on left side); large protarsomere 2 distinctly widening distally; protarsomeres 3 and 4 small; protarsomere 5 elongate and slender; apically one claw visible (possibly an artefact). Middle legs and hind legs long, with distal parts moderately flattened and broadened, modified as paddle-like swimming legs, more distinctly on hind legs ( Figs 1B , 2 , 3A ). Mesocoxa distinctly larger than procoxa, rounded to triangular, with nearly straight and adjacent mesal walls. Mesotrochantin not recognizable. Mesotrochanter distinctly larger than protrochanter. Mesofemur 6.1 mm long, slightly longer than profemur but distinctly broader, and widening distally. Mesotibiae 5.0 mm long, slightly shorter and narrower than femur, also widening distally. Mesotarsus broadened, especially mesotarsomere 1; length formula 2–0.5–0.7–0.4– 1.2 mm; distal tarsomeres only indistinctly visible on left side. Distal part of hind legs similar to corresponding parts of middle legs, but tarsus distinctly larger, apparently functioning as main propulsive organ. Metacoxa transverse, reaching elytral epipleuron laterally, slightly broader than posterior edge of metaventrite; length 3 mm, width 5 mm; posteromedian part covering part of abdominal sternite III ( Figs 2 , 3A ); mesal walls extensively fused; metacoxal plates present but small, not forming duplicatures, anteriorly ending at about half width of anterior coxal margin; rounded posteriorly. Metatrochanter exposed, slightly larger than mesotrochanter. Metafemur 5.8 mm long, metatibia 5.4 mm; both similar to corresponding mesothoracic equivalents. Metatarsus large, distinctly broadened, paddle-like; length formula 2.0–1.0–1.0–1.5–2.0 mm; tarsomere 1 largest; tarsomere 5 cylindrical, with double claw ( Figs 1B , 2 , 3A ). Swimming hairs not recognizable.

Elytral shoulder region obsolete, pronoto-elytral angle thus indistinct. Elytra 20 mm long and maximum width 6.2 mm, distinctly widening posteriorly, widest at about posterior 1/3 (preserved with distal portion of mesal edges separated); posteriorly truncated, with very small posterolateral protuberance and straight posterior edge. Striae or other surface structures not recognizable, elytra apparently smooth. Epipleura fairly narrow, parallel-sided, slightly narrowing anteriorly, posteriorly reaching posterior elytral margin ( Fig. 2 , 3A ).

Abdomen with six exposed sternites (II–VII), widest in middle region, narrowing posteriorly. Sternite II (= ventrite 1) completely divided by median part of metacoxae, sternite III partially ( Figs 2 , 3A ). Sternites II–VI about equally long, with straight posterior margins. Terminal sternite VII about 1.5 times as long as preceding sternites, 2.4 times as wide as long; posterior edge indistinct, apparently sinuate laterally and rounded caudally. Genital complex comprising paired gonocoxosterna and gonocoxae distinctly exposed posterior to sternite VII, tergum VIII and elytra ( Figs 1–3 ). The gonocoxosterna are usually paired structures forming the ventral cover of segment VIII and invaginated in the resting position of the genital apparatus ( Burmeister 1976: figs 3, 4; Balke & Hendrich 2016; see also Bils 1976).

Figures

FIGURE 1. Photographs of Tigrivia baii, holotype, YLSNHM01120, (A) dorsal view; (B) ventral view. Scale bars 3.5 mm.

FIGURE 2. Line drawing of Tigrivia baii, based on holotype, ventral view. Abbreviations: aes1, mesanepisternum; aes3, metanepisternum; cx, coxa; cxpl,coxal plate;ep, episternum;fe, femur;gcxs, gonocoxosterna; gu, gula; kes3, metakatepisternum; lbr, labrum; md, mandible; mt, mentum; pl, propleuron; pmt, prementum; pst, prosternum; pta, protarsi; scu2, mesoscutum; st, sternite; ti1, tibia1; tisp, tibial spur; tr, trochantin; v2, mesoventrite; v3, metaventrite.

FIGURE 3. Reconstruction of Tigrivia baii, based on holotype and drawing, (A) ventral view; (B) dorsal view.