Isoperla lituana, Chen, 2025

Chen, Zhi-Teng, 2025, Three new stoneflies (Insecta: Plecoptera) from Eocene Baltic amber, European Journal of Taxonomy 1026, pp. 107-122 : 116-120

† Isoperla lituana sp. nov.

urn:lsid:zoobank.org:act:

Figs 8–11

Diagnosis

Head generally pale brown, with a light M-shaped pattern. Pronotum narrower than head, width ca 1.5 × as long as length, with angled corners, anterior margin convex, posterior margin almost straight, lateral margins slightly oblique; median suture distinct, lateral areas rugose. Macropterous. In forewing, ScP reaching RA before ra-rp; RP with two branches; CuA with two branches; AA1 simple, AA2 forked. In hind wing, ScP reaching RA before ra-rp; RP with two branches. Tibia with moderate apical spurs. Abdominal terga 1–8 unmodified. Tergum 9 with a subquadrate patch of short stout sensilla basiconica medially. Tergum 10 complete, with depressed, membranous, posteromedial area, anterior and lateral areas of the membrane surrounded by short stout sensilla basiconica similar to those on tergum 9. Paraprocts darkly sclerotized, upcurved, narrow, pointed apically. Sternum 7 with posteromedian extension. Vesicle of sternum 8 absent. Sternum 9 greatly expanded backwards into hood exceeding basal cercal segment, posterolateral margins forming oblique ridges. Cerci slightly shorter than abdomen.

Etymology

The new species is named after Lithuania, where the piece of amber was obtained.

Type material

Holotype

LITHUANIA • ♂; Lithuanian amber , Eocene, Bartonian to Priabonian, ca 34–38 Ma; beach collected; CZT-PLE-BA 9, ICJUST.

Description

Male

BODY. Length (from anterior of head to posterior of abdomen) ca 9.5 mm. Body mostly pale brown ( Fig. 8A–B).

HEAD. Generally pale brown, anteriorly with light M-shaped pattern ( Fig. 9A). Triocellate, anterior ocellus near half in size of posterior ones. Compound eyes large and rounded. Antennae slender, generally dark brown, subequal in length to abdomen. Maxillary palps slender, five-segmented with strongly shortened apical segment; labial palps much shorter, three-segmented with slightly shortened apical segment ( Fig. 9A–B).

THORAX. Pronotum narrower than head ( Fig. 9A), width ca 1.5 × as long as length, with angled corners, anterior margin convex, posterior margin almost straight, lateral margins slightly oblique; median suture distinct, lateral areas rugose. Macropterous; wings hyaline, veins brown ( Fig. 8A–B). Forewings length ca 8.0 mm, hindwings length ca 6.5 mm. In forewing, ScP reaching RA before ra-rp; RP with two branches; CuA with two branches; AA1 simple, AA2 forked. In hind wing, ScP reaching RA before ra-rp; RP with two branches; anal area large and folded. Legs mostly brown, darker at joints of femur and tibia; tibia with moderate apical spurs.

ABDOMEN. Abdominal segments mostly dark brown. Terga 1–8 unmodified. Tergum 9 with subquadrate patch of short stout sensilla basiconica medially ( Fig. 10A–C). Tergum 10 complete, with elliptical, depressed, membranous, posteromedial area, anterior and lateral areas of membrane surrounded by short stout sensilla basiconica similar to those on tergum 9. Paraprocts darkly sclerotized, upcurved, narrow, pointed apically. Sternum 7 with short but wide posteromedian extension ( Fig. 11A–B). Vesicle of sternum 8 less developed, indistinguishable from sternum. Sternum 9 greatly expanded backwards into hairy, rounded hood exceeding basal cercal segment; posterolateral margins of sternum 9 forming oblique ridges. Cerci slender, preserved parts slightly shorter than abdomen, basal segments pale, apical segments dark.

Remarks

Compared with † Isoperla succinica Hagen, 1856 , whose holotype is lost and whose status has been treated as incertae sedis ( Caruso & Wichard 2010; Jouault et al. 2021), † I. lituana sp. nov. can be distinguished by the 8 th cercomere, which is more than 2 × as long as broad (vs barely 2 × as long as wide in † I. succinica ), and by the absence of a median cleft in tergum 10 (vs presence of a cleft in † I. succinica ) ( Jouault et al. 2021). The new species can also be differentiated from † I. baltica by several features, including: the forewing with ScP reaching RA before ra-rp (vs after ra-rp), CuA with two branches (vs three branches), abdominal sterna 9 and 10 with patches of sensilla basiconica (vs lacking sensilla basiconica), and an elongated sternum 9 that exceeds the basal cercal segment (vs not exceeding the basal cercal segment) ( Jouault et al. 2021). In addition to these distinguishing traits, † I. lituana differs from extant species by its unique combination of characters, as outlined in the diagnosis.