Perlodidae

Abstract

3.4.4. Perlodidae Perlodidae fossils are known from two extinct Jurassic genera and two extant Palaeogene genera. Unfortunately, this family lacks established apomorphies and is generally supported by variable characters, such as colouration, that are not visible in many fossils (Zwick 2000). The nymph of † Isoperlodes perstrictus Sinitshenkova is incomplete, without the head or tip of the abdomen preserved. It was assigned to Perlodidae as the wingpads are elongated near the apex, which is similar to the condition of extant Isoperla Banks (Sinitshenkova 1992). This is not an autapomorphy of the family or genus. Nevertheless, † I. perstrictus is probably Systellognathan, as it has a short first tarsomere. † Derancheperla Sinitshenkova clearly falls within Perloidea, supported by the presence of slender mandibles without a mola (suggesting a carnivorous lifestyle), and the loss of the frontoclypeal suture (Sinitshenkova 1990). The nymph shows strong similarities to the nymphs of both Perlidae and Perlodidae, but lacks any clear autapomorphies of either. This absence of apomorphies does not preclude a possible assignment to stem-Perlidae instead of stem-Perlodidae, and therefore this species can be placed confidently only within Perloidea. The presence of a notal contour between the wing pads, present in † Derancheperla, may be derived in Perlodidae. The wing pads are instead rounded and meet medially in Perlidae and Chloroperlidae (Zwick 2000), a trait that appears to have been secondarily lost in the Perlodidae. The type specimens of Isoperla † succinica Hagen and Perlodes † resinatus Hagen have been lost (Caruso & Wichard 2010; Jouault et al. 2021). As the original descriptions are vague, we follow Jouault et al. (2021) in treating their placement as uncertain and exclude them from this review. The assignment of Isoperla † baltica Jouault et al. is relatively well supported. While it is assigned to the Perlodidae predominantly on the absence of any apomorphies of other families, it can be placed within Isoperlinae based on paraprocts modified into simple upcurved hooks, and specifically in Isoperla based on wing venation (e.g., lack of cubital crossveins in the hindwing) (Jouault et al. 2021). Isoperla † baltica also shares the longitudinal thoracic stripe commonly seen in Perlodidae (Zwick 2000).