The genus Vietnamella Tshernova, 1972 is reviewed and 3 valid species are confirmed. They are V. ornata (Tshernova, 1972), V. sinensis (Hsu, 1936) Tshernova, 1972. The nymphal and key imaginal characters of V. sinensis are described and figured. The monogeneric family Vietnamellidae has long series of autapomorphies (two pairs of projections on head, modified mandibles, slender maxillae with few setae, round hindwings, and half of egg covered with single cap) and some plesiomorphies (seven pairs of gills, large hindwings, few marginal intercalaries on forewings). The structures of mouthparts, head and forefemora suggest that nymphs of Vietnamella may be able to move substrates and scrape food from them. Morphological evidences show that the family Vietnamellidae is a basal clade of Ephemerelloidea.

Mayflies (Ephemeroptera) display many primitive characters and a unique type of metamorphosis (Prometabola). However, information on the genomes and transcriptomes of this insect group is limited. The RNA sequencing study presented here generated the first de novo transcriptome assembly of Cloeon viridulum (Ephemeroptera: Baetidae), and compared gene expression signatures among the young larva (YL), mature larva (ML), subimago (SI), and imago (IM) stages of this mayfly. The transcriptome, based on 88 Gb of sequence data, comprised a set of 81,185 high quality transcripts. The number of differentially expressed genes (DEGs) in YL vs. ML, ML vs. SI, and SI vs. IM, was 4,825, 1,584, and 1,278, respectively, according to the reads per kilobase of transcript per million mapped reads analysis, assuming a false discovery rate <0.05 and a fold change >2. Gene enrichment analysis revealed that these DEGs were enriched in the “chitin metabolic process”, “germ cell development”, “steroid hormone biosynthesis”, and “cutin, suberine, and wax biosynthesis” pathways. Finally, the expression pattern of a selected group of candidate signature genes for Prometabola, including vestigial, methoprene-tolerant, wingless, and broad-complex were confirmed by quantitative real time-PCR analysis. The Q-PCR analysis of larval, subimaginal, and imaginal stages of C. viridulum suggests that the development of mayflies more closely resembles hemimetamorphosis than holometamorphosis.

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The nymph and reared male and female of a new ephemerellid species, which was collected from southern China and named Teloganopsis setosa Zhou, sp. n., are described. The nymph is unique because of its long and dense setae on labrum, mandibles, maxillae, labium, and forelegs as well as the elongated segments II of labial palpi and expanded paraglossae. The male can be differentiated from close relatives by its larger penis lobes with dorsolateral projections, and the more pigmented tergum IV and caudal filaments. The nymph described in this paper represents a new adaptive and ecological type in the family Ephemerellidae.

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