The First Described Nymphs and Detailed Imagoes of the Species Thalerosphyrus cingulatus Navás Revealing a New Mayfly Genus from Eastern China (Ephemeroptera: Heptageniidae, Ecdyonurinae) †.

Simple Summary: The reduction or loss of crossveins on colorful wings can be found in several lineages of mayflies, especially those with small to tiny bodies. However, in the family Heptageniidae, whose nymphs have very flat bodies and usually crawl on the surface of rocks to pebbles, this situation is very rare. Surprisingly, about 90 years ago, a Spanish entomologist Longinos Navás briefly described and illustrated a Chinese mayfly, Thalerosphyrus cingulatus, with few crossvein rows which is further heavily pigmented with yellowish to brown stains. Unfortunately, this interesting species and its outstanding morphology have never been re-checked or confirmed until now. In 2021, tens of specimens of this mayfly were re-found and its mating flight behavior was recorded. Therefore, the original characters of this species are re-described and photographed in detail. The results show both its imagoes and nymphs have a long series of combined characteristics of several related genera, and it represents a new clade and owns a new phylogenetic position of the subfamily Ecdyonurinae. To reflect its uniqueness, a new genus, Regulaneuria Zhou, gen. nov., is established herein. The similar venations are found in several families of the order Ephemeroptera. This means the reduction of crossveins can happen repeatedly and convergently in mayflies but our finding here is the extreme one of the family Heptageniidae. The nymph and detailed imaginal morphology of the Chinese mayfly Thalerosphyrus cingulatus have not been reported since it was named by Navás in 1933. Here based on newly collected nymphal and associated imaginal materials of this species from eastern China, we find both nymphs and adults have several extraordinary characters. In adults, forewings have less crossveins in costal and subcostal sections, others crossveins arranged into five regular rows; tibiae and tarsi of midlegs and hindlegs subequal in length; male compound eyes widely separated and penes simple and fused. The nymphs have greatly extended lateral pronotum, round supracoxal spurs and extended dorsal lamellae of gills, especially those of the gills VII; maxillae have two independent distal dentisetae. These combined characters represent a new generic taxon. Therefore, Regulaneuria Zhou, gen. nov. is established here to include the species Regulaneuria cingulata (Navás, 1933) comb. nov. The forewing venation of the species R. cingulata is unique in the family Heptageniidae but similar to some counterparts of Leptophlebiidae and Baetidae. [ABSTRACT FROM AUTHOR]