Large intergenic spacers and tRNA gene duplications have been reported in several insect groups, although little is known about mitogenomes of mayflies. Here, we determined complete mitogenomes of ten heptageniid species and systemically analyzed their mitogenomic features. Both a conserved intergenic spacer (IGS) and trnM duplication were detected in those mitogenomes. The IGS, which was observed in heptageniids, could be further folded into a stable stem–loop structure. The tRNA gene duplication was found in almost all analyzed mitogenomes, and a unique gene block trnI-trnM-trnQ-trnM-ND2 was also discovered. Our analysis demonstrates that the heptageniid gene arrangement pattern can be explained by the tandem duplication-random loss (TDRL) model. Phylogenetic analyses using both Bayesian inference (BI) and maximum likelihood (ML) methods based on the nucleotide and amino acid sequence data recovered the genus Epeorus as monophyletic with strong support. Our results provide a better understanding of mitogenomic evolution in Heptageniidae, as well as novel molecular markers for species identification of mayflies.

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The genus Afronurus has several very common mayfly species in China and they are widely distributed in this country. Some of them are quite similar to each other in both imaginal and nymphal stages. However, these species have not been systematically compared and reviewed so far. In this study, six species are recognized. All nymphs of them share the following characters: gills V–VI with additional arrow-like accessory lobes, branched dentisetae, two rows of bristles and setae on hindtibiae and spotted abdominal terga. The males have divergent penes and clearly expressed titillators. The nymphs of the new species A. drepanophyllus sp. nov. have sickle-like gills I, spotted and striped body color, and males have unique genitalia. The nymphal stages of A. furcatus and A. hunanensis, which are associated and described for the first time, have similar body color to A. drepanophyllus sp. nov., but their pale dots on the head capsules and the shape of the hypopharynx are different. Keys to males and nymphs of the six species are provided.

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.