Overview
In Australia this family is represented by
Tasmanocoenis
(5 spp.) (Suter 1984). Adults of
Tasmanocoenis
frequently swarm along the margins of streams in the early morning in temperate Australia. In tropical species swarming may occur at night at sites remote from water (Marchant 1982).
Description
Like the nymphs of
Tasmanophlebia
, nymphs of
Tasmanocoenis
have an operculate abdominal gill covering the other gills, but in
Tasmanocoenis
it is the second gills rather than the first, and the operculate gills are fringed with fine hairs. Nymphs of
Tasmanocoenis
are also considerably smaller than those of
Tasmanophlebia
. Adults of
Tasmanocoenis
are small but distinctive; the sexes are alike, with eyes of similar size, and the hind wings are absent. The fore wings are broad and fringed with fine hair.
Distribution
Nymphs are widespread in Tas. and the mainland, occurring especially in silty areas of stony streams or rivers, and also in standing waters. Their diet seems to consist mainly of fine detritus (Chessman 1986) and they are among the more pollution-tolerant of Australian mayflies.
T. tillyardi
in S.A. streams has 1 or 2 generations per year with multiple cohorts continuously present (Suter 1980; Suter and Bishop 1980).
T. tonnoiri
is bivoltine in the La Trobe R, while another unnamed species is univoltine (Marchant et al. 1984). For all 3 species the emergence period is spring-summer, and for the first 2, adults emerge for 5 months or more. In the tropical Magela Ck system, a species of
Tasmanocoenis
similar to
T. tillyardi
has a nymphal development time of about 4 weeks on average and as short as 2 weeks (Marchant 1982), with adults emerging year round.