Heterotrissocladius changi Saether

Heterotrissocladius changi Saether

Figs 22A–D

Diagnosis. Labrum as in Fig. 22A; SI seta plumose; pecten epipharyngis with 3 serrated scale-like spines; antenna (Fig. 22B) 7-segmented, basal segment 58 µm long, 3 rd reduced, shorter than the 4 th and 7 th indistinct hair-like, AR 0.9; mandible as in Fig. 22C; mentum (Fig. 22D) with pair of median teeth, basolaterally with short extension; VM plate broad, V/M 1.4; procercus sclerotized, short, about as long as wide with 7 apical setae; anal tubules curved half as long as posterior parapod.

Notes. The unpigmented submentum and broad VM plates will separate H. changi from other members within the H. marcidus group, except for possibly Heterotrissocladius boltoni Saether, which is recorded only from Ohio. Saether (1995: 38) points out that Metriocnemus aequalis Johannsen should be assigned to Heterotrissocladius and may in fact be a senior synonym of H. changi or Heterotrissocladius hirtapex Saether.

Ecology and habitat. Although the species typically occurs in littoral to upper profundal zones of oligotrophic lakes, it occurred in study streams with H. marcidus. This species is bivoltine with a major emergence in the spring till June and a minor one in early fall, although an emergence of June till mid August has been reported for two lakes, Lake Waterton, Alberta and Green Lake, Colorado. (Saether 1975).

Sampling sites. We found the larvae inhabiting streams in all the provincial parks and districts located in our study area.

Nearctic distribution. Canada: Northwest Territories, Alberta, Manitoba, Saskatchewan, and Ontario. USA: Colorado, Illinois, Indiana, Michigan, Minnesota, New York.