Gill Movements of Nymphal Ephemera Danica (Ephemeroptera) and the Water Currents Caused by them

Abstract

The nymphs of Ephemera danica living in burrows in the sandy mud of flowing waters present a problem of current production in the water, quite different from those so far investigated (Eastham, 1932, 1934, 1936, 1937)-Percival & Whitehead (1926) collected data indicating that this species is found most commonly in water, flowing over a sandy floor, which contains about 65% coarse sand, 2% fine sand and about 1 % each of silt, fine silt and clay. Their observations also showed that from this type of environment there was little or no migration to neighbouring places where the sand was present in smaller amount and the silt and clay predominated. Experiments showed that the animals always displayed a preference for the soft surface into which burrowing could be effected, but no adequate explanation of the relationship between nymphs and sand was forthcoming. Questions regarding the unsuitability of silt or clay, in any but small quantities, remain unanswered.