Izyumochauliodes aristovi Prokin & Bashkuev, 2023

PROKIN, ALEXANDER A. & BASHKUEV, ALEXEY S., 2023, The oldest known larvae of Megaloptera (Insecta) from the Triassic of Ukraine, Palaeoentomology 6 (2), pp. 155-164 : 159-161

Izyumochauliodes aristovi Prokin & Bashkuev sp. nov.

( Figs 1–5 )

Type material. Holotype: PIN 3320 /33, impression (part and counterpart) of complete dorso-ventrally compressed larva . Paratypes: PIN 3320 /32 (without counterpart), larva without head ; PIN 3320 /38, ventro-laterally compressed incomplete larva; 3320/64 (counterpart only), nearly complete larva without legs; 3320/35 (without counterpart), anterior part of larva with head, thorax and basal abdominal segments, without legs .

Etymology. Dedicated to the memory of Daniil S. Aristov, our friend and colleague, who prematurely passed away in 2022 at the age of 43, for his great contribution to the taxonomy and systematics of fossil insects.

Diagnosis. As for genus.

Locality and horizon. Ukraine, Kharkiv Region, Izyum District, right bank of the Bereka River (tributary of the Seversky Donets River), 3 km north of Velikaya Kamyshevakha, Dolgy Jar ravine, Garazhovka locality; Upper Triassic, upper Carnian—lower Norian, Protopivka Formation.

Description. Total length of larva, 9.5–14.8 mm (12.0 in holotype), length of pronotum 1.5–1.6 mm (1.5), width of pronotum 1.8–2.2 mm (1.8), length of head 0.8– 1.4 mm (1.0), width of head 1.2–1.5 (1.2). Neck region about 0.3 of total length of head. Basisternum about two times longer than coxal cavities and two times shorter than tergite of pronotum. Tergites of mesonotum equal in length to metanotal tergites and 2.75 times shorter than pronotal tergites. Obscure internal organ (most possibly proventriculus) is seen between segments III and IV. Respiratory tubes about 7 times longer than wide, nearly half as long as lateral filament of segment VIII. Proleg more than twice longer than wide.

Family Sialidae Leach in Brewster, 1815

Subfamily incertae sedis

( Fig. 6A )

Remarks. The new fossil larva (PIN 3320/34, preserved in lateral view) is assigned to Megaloptera , Sialidae based on the following characters: head large, thorax flattened and robust, with prothorax longer than meso- and metathoraces, with heavily sclerotized and quadrangular pronotum; abdomen elongate, abdominal segments with lateral filaments (their number is unknown), segment X with long tapering median filament; legs long, nearly one third as long as body length. Total length of the larva, 11.3 mm, length of head, 1.6 mm.

Abdominal lateral filaments (tracheal gills) are poorly preserved and their number is unknown, which preclude us from attributing the new larva to a particular subfamily. However, considering that Sharasialinae (in contrast to Sialinae) have tracheal gills on the 8th abdominal segment, which is considered a plesiomorphic condition, and the even more ancient, Triassic, age of the new larva, the tracheal gills on its segment VIII can be expected.

Larvae of Coleoptera known to have the segment X protruding to a long caudal filament ( Haliplidae , as well as fossil Kargalarva permosialis Prokin et al., 2019 from the Middle Permian of Kargala and Trialarva koburgensis Prokin & Bashkuev, 2020 from the Upper Triassic Hassberge Formation in Lower Franconia) all have a relatively small head that is shorter and narrower than the pronotum, in contrast to Megaloptera , including the newly reported sialid larva.

Figures

FIGURE 1. Fossil larva Izyumochauliodes aristovi gen. et sp. nov., holotype PIN 3320/33.A, B, Photograph (part and counterpart). C, Line drawing of the body, dorsally. D, Line drawing of the body, ventrally. Scale bars = 2 mm.

FIGURE 2. Fossil larva Izyumochauliodes aristovi gen. et sp. nov., photographs of paratypes. A, PIN 3320/32. B, PIN 3320/38. Scale bars = 2 mm.

FIGURE 3. Fossil larva Izyumochauliodes aristovi gen. et sp. nov., photographs of paratypes. A, PIN 3320/64. B, PIN 3320/35. Scale bars = 2 mm (A), 1 mm (B).

FIGURE 4. Morphological details of Izyumochauliodes aristovi gen. et sp. nov. A, PIN 3320/38, abdominal segment X with prolegs. B, PIN 3320/32, respiratory tubes.Abbreviations: cl—claws of prolegs, lf—lateral filament of segment X, RT—spiracular opening of respiratory tube. Scale bars = 1 mm (A), 0.5 mm (B).

FIGURE 5. Morphological details of Izyumochauliodes aristovi gen. et sp. nov. A, PIN 3320/33, head. B, PIN 3320/64, head with mandible. C, PIN 3320/33, cervical segment and prothorax. Abbreviations: bst—basisternum, ccav—coxal cavities of prothorax, cer—jugulare of cervical segment, cri— occipital suture, mdt—mandibular teeth, mtscl—sclerotisations of mentum. Scale bars = 0.5 mm.

FIGURE 6. Fossil Megaloptera from Garazhovka locality, photographs. A, Sialidae, subfamilia incertae sedis, PIN 2230/34. B, Megaloptera, familia incertae sedis, PIN 3320/36. C, Megaloptera, familia incertae sedis, PIN 3320/37. Abbreviations: cf—end of caudal filament of segment X, h—head, l1—tip of foreleg, l2—tip of midleg, l3—tip of hindleg, mst—mesothorax, mmt— metathorax, pt—prothorax. Scale bars = 2 mm (A), 1 mm (B), 0.5 mm (C).