Palaeopsole spinosa, Chen, 2025

Chen, Zhi-Teng, 2025, Three new stoneflies (Insecta: Plecoptera) from Eocene Baltic amber, European Journal of Taxonomy 1026, pp. 107-122 : 109-112

† Palaeopsole spinosa sp. nov.

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Figs 1–3

Diagnosis

Epiproct slender (wider in P. weiterschani ); paraprocts sharp (rounded in P. weiterschani ); cerci without humps (with humps in P. weiterschani ); lateral projections of tergum 10 obtuse (pointed in P. weiterschani ); ra-rp reaching RP after fork point (at fork point in P. weiterschani ).

Etymology

The specific epithet refers to the spine-shaped epiproct of the holotype.

Type material

Holotype ( Fig. 1A–B)

LITHUANIA • ♂; Lithuanian amber , Eocene, Bartonian to Priabonian, ca 34–38 Ma; beach collected; CZT-PLE-BA 6, ICJUST.

Description

Male

BODY. Slender ( Fig. 1C–D), length (excluding antennae) ca 3.0 mm. Macropterous; generally dark brown.

HEAD. Dark and rounded, much wider than pronotum ( Fig. 1C). Triocellate; compound eyes large and protruded. Antennae filiform and dark brown, preserved segments almost equal with body length, with about 29 segments plus scapus and pedicellus, each segment covered with short bristles. Maxillary palp four-segmented, basal segment shortest, apical three segments subequal in size. Labial palp extremely short.

THORAX. Pronotum rectangular and dark brown, much longer than its width ( Fig. 1C). Mesothorax and metathorax darkly sclerotized, much wider than prothorax. Legs generally brown ( Fig. 1C–D); tibia thinner and slightly longer than femur, ventroapically with two giant spurs. Tarsus with three segments; first and third segments subequal in length, second segment shortest.

WINGS. Forewings length ca 4.0 mm ( Fig. 1C–D). In forewings, ScP reaches RA before ra-rp; RP originated from near base of RA, forked before ra-rp and at near half length of the wing; M forked before the fork of RP; Cu basally forked to CuA and CuP; area between M and CuA with six crossveins in left forewing and seven crossveins in right forewing; area between CuA and CuP with ten crossveins in left forewing and seven in right forewing; AA1 curved, AA2 forked. Hind wings rolled, veins invisible.

ABDOMEN. Short, near ⅓ of body length ( Fig. 1C–D). Terga 1–8 generally pale. Terga 9–10 sclerotized laterally and membranous medially ( Fig. 2A–D). Posterior margin of tergum 9 projected with pale long spine, length of spine near half of tergum 9. Central area of tergum 10 generally pale, without obvious sclerite; lateral parts of tergum 10 rounded and unmodified, without projections. Epiproct hook-shaped with sharp apex, abruptly curved upwards; basal cushion of epiproct broad and wide, laterally with two bilobed plates. Paraprocts (subanal lobes) long, visible apical half semielliptical with sharp apex. Sternum 9 sclerotized, apically with distinct subgenital plate as wide as long and rounded apically, basally with oval vesicle (ventral lobe), which with length 1.5 × as long as its width ( Fig. 3A–B). Cerci short and near cylindrical, apical half strongly sclerotized, hemispherical in shape.

Remarks

The slightly rolled wings, absence of the X-pattern of crossveins at the cord, and the unsegmented cerci collectively assign † P. spinosa sp. nov. to the family Leuctridae . The species’ small and simple epiproct excludes its affiliation with the subfamily Megaleuctrinae ( Zwick 2000) . Its high morphological similarity to the extant genus Rhopalopsole Klapálek, 1912 suggests that it belongs to the subfamily Leuctrinae . The presence of a posteromedial spine on abdominal tergum 9, combined with its Eocene origin, confirms † P. spinosa as a member of the extinct genus † Palaeopsole Caruso & Wichard, 2011 . The original definition of † Palaeopsole was based solely on the type species, † P. weiterschani , and several characters of † P. spinosa do not align with the type. Notably, the two long, triangular paraprocts of † P. spinosa resemble those in Leuctra , in which males have two slender median specilla adapted for sperm transfer ( Pardo & Zwick 1993; Zwick 2000). The apical half of the cercus in † P. spinosa is strongly sclerotized into a distinct hemisphere, a feature absent in all known Leuctridae , including its only congener, † P. weiterschani .