Izyumochauliodes 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 : 156-159

Izyumochauliodes Prokin & Bashkuev gen. nov.

Type species. Izyumochauliodes aristovi sp. nov.

Composition. Type species only.

Etymology. From the Ukrainian city of Izyum, in reference to the geographical location of the type locality in the Izyum district, and Chauliodes Latreille, 1796 (a genus-group name of Chauliodinae ), in reference to the affinity of the new genus to Chauliodinae . Gender masculine.

Diagnosis. Head subquadrate, slightly shorter than wide. Coronal suture (= epicranial stem) quite short, paired frontal sutures break at obtuse angle, occipital suture connected with coronal at its base. Mandible dark with evenly curved inner margin, apical tooth acute and tapered, approximately 3 times as long as preapical. Cuticular ridge delimiting neck region ventrally directed forward along gula and reaching submentum. Mentum with rectangular narrowly divided sclerotisations. Postgular sclerite about one-third as long as gula with submentum. Cervical segment short, jugulare (sternal sclerite) sclerotised. Prothorax subquadrate, slightly wider than long, widest at base, with spiracular openings at membranous basal part. Pronotal sclerotised tergite darkened. Basisternum heavily sclerotised. Mesothorax 1.5 times shorter than pronotum, with spiracular openings at membranous basal part; dark sclerotised tergites of mesonotum trapezoidal with anterior margin wider than posterior, straight inner and oblique lateral margins. Metathorax slightly shorter than mesothorax, dark sclerotised tergites of metanotum with anterior margin wider than posterior, lateral margin oblique, posterior and inner margins converging inwards. Procoxal cavities transverse and contiguous. Femora straight with regular row of setae, slightly longer than tibiae, which are dilated to the top and two times longer than tarsus, which is equal to claws in length.Abdomen longer than head plus thorax, with segments I–VIII bearing slender, distally tapering lateral filaments, slightly longer than width of respective segments. Tracheae with weakly pronounced taenidiae. Abdominal segment VIII posteriorly with pair of equally long respiratory tubes. Abdominal segment X with pair of prolegs about half as long as total length of segment X; proleg with pair of curved claws equal in length to width of proleg. Lateral filament located at base of segment X and equal in length to complete segment with prolegs.

Remarks. The new genus is assigned to Megaloptera , Corydalidae , Chauliodinae based on the following characters: head large, with ridge delimiting neck region (occipital or postoccipital suture), posteromedian part of head capsule formed by gula fused with submentum, and distinct postgular sclerite, mentum with sclerotisations; cervical segment with heavily sclerotised sclerite ventrally (jugulare); the thorax is flattened and robust, with the prothorax longer than meso- and metathoraces and a heavily sclerotized and quadrangular pronotum; the ecdysial line continues posteriorly from coronal suture of the head along the whole length of the thorax dorsally; the basisternum is heavily sclerotized; abdomen 10-segmented, segments I–VIII with lateral filaments (tracheal gills), at the base of lateral filament segments I– VII with the spiracular openings, segment VIII spiracles protruding into respiratory tubes, segment X with pair of prolegs, each of which bears a lateral filament and two hook-like claws.

Comparison. Larvae have been described for 14 extant genera of Chauliodinae : Anachauliodes Kimmins, 1954 , Apochauliodes Theischinger, 1983 , Archichauliodes van der Weele, 1909 , Chauliodes Latreille, 1796 , Dysmicohermes Munroe, 1953 , Madachauliodes Paulian, 1951 , Neochauliodes van der Weele, 1909 , Neohermes Banks, 1908 , Nigronia Banks, 1908 , Orohermes Evans, 1984 , Parachauliodes van der Weele, 1909 , Platychauliodes Esben-Petersen, 1924 , Protochauliodes van der Weele, 1909 and Taeniochauliodes Esben-Petersen, 1924 ( Rivera-Gasperín et al., 2019; Tu et al., 2019). Fossil larvae are known for four species of the subfamily: Cretochaulus lacustris Ponomarenko, 1976 from Early Cretaceous Baissa locality, Transbaikalia, Russia, Jurochauliodes ponomarenkoi Wang & Zhang, 2010 and Eochauliodes striolatus Liu et al., 2012 from Haifanggou Formation, Middle Jurassic: Inner Mongolia, China, and Chauliosialis sukatshevae Ponomarenko, 1976 from Early Cretaceous Taymyr amber (see discussion). In addition, the larval “new morphotype 4” from mid-Cretaceous Burmese amber reported by Baranov et al. (2022), can also be attributed to Chauliodinae as an undescribed new genus.

The peculiar characters of the head, such as the cuticular ridge delimiting neck region (occipital suture) ventrally directed forward along gula and reaching submentum, and shape of mandibula allow to distinguish Izyumochauliodes gen. nov. from all known Resent and fossil Corydalidae , including Chauliodinae . In fact, these characters are more typical of Sialidae than of Corydalidae . All known Corydalidae are characterized by a circular ridge ending at the antero-lateral edge of the postgular sclerite or connected with the gular part or the gula+submentum fused “gulasubmentum”; mandibles with straight row of additional teeth and, thus without an evenly curved inner margin. Some additional characters, preserved in Izyumochauliodes gen. nov., are informative for the comparison with other genera. According to Tu et al., (2019), larvae of Anachauliodes and Chauliodes are characterized by long and asymmetric right and left respiratory tubes on the eighth abdominal segment, while in larvae of Madachauliodes , Neohermes , Orohermes , Protochauliodes and the subgenus Archichauliodes van der Weele, 1909 , respiratory tubes are much shorter and only slightly protruded from the abdominal surface ( Tu et al., 2019), same as in all previously described fossil larvae ( Cretochaulus lacustris , Jurochauliodes ponomarenkoi , Eochauliodes striolatus and, possibly, “morphotype 4” of Baranov et al., 2022). Thus, Izyumochauliodes gen. nov. belongs to a group of genera possessing quite long and symmetric (equal in length) respiratory tubes, which according to Tu et al., (2019) includes the following genera: Apochauliodes , Dysmicohermes , Neochauliodes , Nigronia , Parachauliodes , Platychauliodes , Taeniochauliodes , and Archichauliodes subgenus Riekochauliodes Theischinger, 1999 , with an new addition of the fossil Chauliosialis sukatshevae . Among these taxa with symmetric respiratory tubes, the distinctly large sclerotised region of mentum (which is observed in Izyumochauliodes gen. nov.) is known for larvae of Australian Apochauliodes, Oriental and East Palaearctic Neochauliodes and Parachauliodes , as well as South African Platychauliodes and Taeniochauliodes ( Tu et al., 2019) . Head wider than long, considered as apomorphic condition by Liu et al. (2012), may be a possible synapomorphy (or symplesiomorphy) of Izyumochauliodes gen. nov., Jurochauliodes ponomarenkoi , Chauliosialis sukatshevae and extant North American genera Dysmicohermes and Orohermes .