Baltileuctra dewalti Chen, 2022

Chen, Zhi-Teng & Liu, Hong-Ling, 2022, A new needle stonefly with parasitic mites from the Eocene Baltic amber, Acta Palaeontologica Polonica 67 (3), pp. 649-654 : 649-653

publication ID	https://doi.org/ 10.4202/app.00984.2022
persistent identifier	https://treatment.plazi.org/id/03E387B7-6436-AB17-FCF2-FA00FF69B98A
treatment provided by	Felipe
scientific name	Baltileuctra dewalti Chen
status	sp. nov.

Treatment

Baltileuctra dewalti Chen View in CoL sp. nov.

Figs. 1–3 View Fig View Fig View Fig .

ZooBank LSID: urn:lsid:zoobank.org:act:662DFF67-70D3-4085-ADE7-12DFF421C526

Etymology: Named for R. Edward DeWalt, who has made substantial contributions to the knowledge of Plecoptera .

Holotype: ICJUST CZT-PLE-BA8, male, a complete specimen in a clear and well-preserved piece of Baltic amber from Lithuania, Eocene (ca. 40–50 Ma).

Type locality: Unknown locality in Lithuania.

Type horizon: Eocene Baltic Amber.

Material. — Holotype only.

Diagnosis.—The ra-rp crossvein located distal to the fork of RP in forewings but basal to it in hind wing; MP partially fused with CuA in hind wing. Median area of terga 8–9 membranous. Tergum 8 with a deep median notch on posterior margin. Tergum 9 with two semicircular posterior sclerites. Tergum 10 medially with a longitudinal, narrow split, posteriorly followed by a fusiform sclerite. Sternum 9 with an elliptical vesicle, length of which 1.5 times longer than wide. Sternum 9 medially and posterolaterally membranous, posteriorly projected as a rounded lobe with two slender oblique sclerites. Subanal probe elongated and curved ventrad, apex enlarged ventrally. Sternum 10 developed innerly, forming two long spines lateral to subanal probe, the spines denticulate ventrally, apex pointed and slightly curved. Cercus elongated and cylindrical, apically with a membranous area and a stout spine.

Description. —Macropterous ( Fig. 1 View Fig ); body length ca. 5.0 mm, generally dark brown; ventral surface covered by unknown white substance. Head rounded and entirely dark brown, much wider than pronotum. Triocellate; compound eyes large and bulbous. Antennae dark and filiform, subequal in length to body, with 36 segments preserved, each segment covered with dense short setae. Maxillary palp four-segmented, apical segment longest; labial palp very short and hardly visible. Pronotum elongated, near rectangular, corners obtuse. Cervical gills absent; cervix with small lateral nubs. Meso- and metathorax much wider than prothorax. Legs generally dark brown; forelegs shortest, hindlegs longest; femur slightly shorter but much thicker than tibia; tibia with two giant ventroapical spurs; tarsus three-segmented, each segment covered with dense setae, second segment shortest; claws short and sharp. Ventral sclerites of thorax invisible. Wings sub-hyaline and fringed with short setae, without any characteristic patterns; veins dark brown ( Figs. 1 View Fig , 2 View Fig ). Left forewing length ca. 5.5 mm ( Fig. 2A View Fig 1 View Fig , A 2 View Fig ); ScP reaches RA before ra-rp, distally almost touching anterior wing margin; one basal humeral crossvein present between anterior margin and ScP; RP and M with separate origins; RP originated from basal 1/5 of RA, forked near apical 1/3 of forewing; ra-rp located distal to the fork of RP; Cu basally forked into CuA and CuP; four crossveins present between M and CuA; area between CuA and CuP with eight crossveins, terminal one jointing posterior margin of the wing; AA1 curved at half length, apical half divergent from CuP; AA2 forked. Visible venation of right forewing similar to left forewing ( Fig. 2A View Fig 1 View Fig , A 3 View Fig ), terminal crossvein between CuA and CuP jointing CuP near apex. Hind wings length ca. 5.0 mm ( Fig. 2A View Fig 4 View Fig , A 5 View Fig ); ScP reaches RA before ra-rp; ra-rp located basal to the fork of RP; MA simple; MP fused with CuA for a short distance; basal parts of CuP, AA1, and AA2 invisible; anal area small and folded, with very few anal veins. Abdomen generally dark brown ( Fig. 1 View Fig ), terga 9–10 darker; terga and sterna of abdominal segments 1–8 divided by conspicuous membrane. Abdominal terga without sclerotized, paired processes. Median area of terga 8–9 completely membranous ( Fig. 3A View Fig 1 View Fig , A 2 View Fig ). Posterior margin of tergum 8 with a deep median notch. Tergum 9 with two extra semi-circular sclerites at posterior margin. Tergum 10 short, darkly sclerotized, medially with a longitudinal, narrow split; a fusiform sclerotized plate present posterior to tergum 10 ( Fig. 3A View Fig 1 View Fig , A 2 View Fig ). Ventral vesicle of sternum 9 elliptical ( Fig. 3A 3 –A View Fig 5 View Fig ), length 1.5 times longer than wide. Sternum 9 with a median membranous area which posteriorly connected with the circular posterior margin of sternum 9 ( Fig. 3A 3 –A View Fig 5 View Fig ); sternum 9 projected backwards, forming a rounded posteromedial lobe with two slender oblique sclerites, the two sclerites originated from half length of sternum 9, gradually converged backwards but never touched; posterolateral areas of sternum 9 completely membranous, with several transverse folds. Subanal probe elongated and slightly curved ventrad from lateral view, apex apparently enlarged ventrally; ventral surface somewhat concaved medially and longitudinally ( Fig. 3A 3 –A View Fig 5 View Fig ). Sternum 10 seems cleft, each hemisternum developed innerly, respectively forming a long spine lateral to subanal probe; the spines slightly longer than cerci but much shorter than subanal probe, denticulate along ventral margin, apex pointed and slightly curved ventrad

Fig. 3A 3 –A View Fig 5 View Fig ). Cercus hairy, elongated and cylindrical, much shorter than subanal probe, apically with a membranous circular area and a stout, dark spine ( Fig. 3 View Fig ).

Remarks.—The new needle stonefly undoubtedly belongs to the family Leuctridae due to its needle-like habitus, absence of gills, apical segment of labial palp similar to other segments, absence of X-patterned crossveins in forewings, second tarsal segment shorter than first and third segments, and one-segmented cerci ( Stewart and Stark 2008; Chen and Du 2018). Additionally, in forewing CuA is simple, and the antero-distal cell lacks a cross-vein, a combination of traits which, within Systellognatha, indicate a Leuctridae ( Béthoux et al. 2015) . At the subfamilial level, the new stonefly is unlikely to fit in the single genus of Megaleuctrinae, Megaleuctra Neave, 1934 , which is characterized by large body size (about 15 mm), presence of six anal veins in hind wings, elaborate epiproct and abruptly recurved subanal probe ( Zwick 2000; Ham and Bae 2002; Baumann and Stark 2013). When compared with the extant species of Leuctrinae, the ra-rp crossvein of the new stonefly is located distal to the fork of RP in forewings but basal to it in hind wing, which is uncommon among Leuctridae and can easily distinguish it from species of Calileuctra Shepard and Baumann, 1995 ( Shepard and Baumann 1995), Paraleuctra Hanson, 1941 ( Stark and Kyzar 2001; Chen 2019b), Perlomyia Banks, 1906 ( Nelson and Hanson 1973), Pomoleuctra Stark and Kyzar, 2001 ( Stark and Kyzar 2001), Rhopalopsole Klapálek, 1912 ( Kawai 1968; Chen 2019a), and Zealeuctra ( Caruso and Wichard 2010) . For the species of remaining extant genera without detailed wing venation description, the new stonefly differs from species of Despaxia Ricker, 1943 , and Moselia Ricker, 1943 , by the presence of a well-developed subanal probe ( Kondratieff and Lechleitner 2002; Stark and Harrison 2016); of Pachyleuctra Despax, 1929 , by the medially cleft tergum 10 and absence of strongly recurved paraprocts ( Stark and Nelson 2019); of Tyrrhenoleuctra Consiglio, 1957 , by presence of paired lateral spines along subanal probe (or namely paraprocts) ( Stark and Nelson 2019); of Leuctra Stephens, 1836 by presence of a much longer, medially cleft abdominal tergum 10, and absence of an elevated, club-shaped epiproct (or namely supraanal organ, process, lobe, etc.) ( Ricker and Ross 1969; Pardo and Zwick 1993). The wing venation and especially the male terminalia of the new species is very similar to that of B. foraminis Chen, 2018a ( Fig. 4 View Fig ) and support its attribution to Baltileuctra Chen, 2018a ( Chen 2018a). The original illustration of B. foraminis neglected the hind wings and paired lateral spines of terminalia, which are provided herein ( Fig. 4 View Fig ). The presence of apical cercal spines, absence of subapical lateral dentation on subanal probe, and presence of isolated, slender, lateral spines near subanal probe can distinguish species of Baltileuctra from Euroleuctra ( Fig. 5 View Fig ; Chen 2018a, b). Within Baltileuctra , the newly described species can be separated from B. foraminis by the following terminalia characters: posteromedial sclerites of sternum 9 interrupted (connected in B. foraminis ); subanal probe curved ventrad (curved upward in B. foraminis ); lateral spines of subanal probe dentate (smooth in B. foraminis ). The partially fused MP with CuA in hind wings of Baltileuctra corresponds with the defining character state of Collaleuctrida as defined in the phylogenetic and nomenclatural framework of needle stoneflies proposed by Béthoux et al. (2015).