Siphlonuridae

Distinguished from other Ephemeroptera families by the combination of: unnotched labrum, antennae shorter than twice head width, maxillae lacking prominent golden spine rows, and rounded abdominal gills of uniform structure. Three caudal filaments are subequal in length. Keys to Fennoscandian species exist for both adult and nymphal stages. Nymphs of some congeners can be separated by size class and habitat association.

Adults possess three long slender caudal filaments of approximately equal length. The labrum (upper lip) lacks a median notch. Antennae are shorter than twice the head width. Nymphs have rounded abdominal gills that are similar to each other in structure. Maxillae on the underside of the head lack prominent rows of golden spines. Sexual dimorphism in size has been observed in some species, with females averaging larger than males in final instars.

Cool freshwater environments including temporary ponds, streams, and river floodplains. Specific habitat preferences vary by species and life stage. In Siphlonurus typicus, nymphs develop in temporary ponds. In Oniscigaster wakefieldi, small nymphs (1–10 mm) occupy fine sediments in quiet shallow water; medium nymphs (11–18 mm) inhabit pebble substrates in silt matrices up to 50 cm deep; mature nymphs (19–26 mm) occur adjacent to emergent boulders at riffle bases. Siphlonisca aerodromia nymphs occupy stream main channels and adjacent Carex floodplains following snowmelt.

Northern Hemisphere temperate regions. Documented from: eastern North America (Connecticut, Maine, Vermont), western North America, Fennoscandia (Finland, Sweden, Norway, Denmark), Russian Far East, and New Zealand. Specific distribution varies by genus and species.

Adult emergence generally occurs in late spring to early summer. Siphlonurus typicus: 27 May to 21 June in Connecticut. Siphlonisca aerodromia: late May or early June in Maine. Oniscigaster wakefieldi: studied July 1965–November 1966 with year-round nymphal presence. Nymphal development typically spans winter to spring months.

Nymphal diet shifts with season and habitat. Siphlonisca aerodromia nymphs initially feed on detritus at near 0°C water temperatures; following snowmelt, animal material including mayfly nymphs becomes increasingly common in floodplain habitats.

Univoltine life cycle documented in multiple species. Siphlonurus typicus: nymphal development March–June, 11 maturity classes identified, degree days excellent predictor of population maturity (r²=0.963). Siphlonisca aerodromia: small nymphs appear in January, adults emerge late May–early June, approximately 394 eggs per female, eggs deposited in stream main channel. Oniscigaster wakefieldi: 20–25 larval instars over 17-month period. Female-biased sex ratios observed in some populations (Siphlonurus typicus at 1.35:1 at one site).

Oviposition occurs directly on water bodies, inlets, and outlets, indicating populations result from both local migrants and permanent residents. Nymphs exhibit ontogenetic habitat shifts, with size classes occupying distinct microhabitats. Following snowmelt, nymphs may move from main channels into adjacent floodplain vegetation.

• BaetidaeBoth families contain small minnow-like mayflies; Siphlonuridae distinguished by unnotched labrum, shorter antennae relative to head width, and rounded uniform gills versus often more differentiated gill structures in Baetidae
• HeptageniidaeFlattened body form and gill placement differ; Siphlonuridae nymphs lack the dorsoventral flattening and gill opercula characteristic of Heptageniidae

• Ephemeroptera
• mayflies
• primitive minnow mayfly
• cool water
• univoltine
• temporary ponds
• freshwater insects

• BugGuide
• Wikipedia
• GBIF taxonomy match
• iNaturalist taxon
• NCBI Taxonomy
• Catalogue of Life
• The Occurrence and Biology of Siphlonisca Aerodromia Needham (Ephemeroptera: Siphlonuridae) in Maine, U.S.A.
• Two new species of Parameletus Bengtsson, 1908 (Ephemeroptera: Siphlonuridae), and notes on other species from the Far East of Russia
• Life history aspects of the mayfly Siphlonurus typicus (Ephemeroptera: Siphlonuridae) with a new application for measuring nymphal development and growth
• Life History and Ecology of Siphlonurus mirus Eaton (Ephemeroptera: Siphlonuridae) in an Intermittent Pond
• The genus <i>Metretopus</i> (Ephemeroptera, Siphlonuridae) in Fennoscandia - identification, faunistics and natural history
• The life history, nymphal growth rates, and feeding habits of Siphlonisca aerodromia Needham (Ephemeroptera: Siphlonuridae) in Maine
• Redescription of Parameletus chelifer Bengtsson and P. minor (Bengtsson), with keys to nymphal and adult stages of the Fennoscandian species of Siphlonuridae (Ephemeroptera)
• Molecular data and species distribution models reveal the Pleistocene history of the mayfly Ameletus inopinatus (Ephemeroptera: Siphlonuridae)1
• Studies on the larva of Oniscigaster wakefieldi (Ephemeroptera: Siphlonuridae) in Waitakere stream, Auckland