MICROHABITAT OF ANTHOPOTAMUS-VERTICIS (EPHEMEROPTERA, POTAMANTHIDAE)

A field and laboratory study was designed to elucidate the microhabita t of the North American riverine mayfly Anthopotamus verticis (Say). P revious reports have suggested that these mayflies are surface sprawle rs or clingers; but despite a flattened body shape that is often assoc iated with sprawling or clinging benthos, our investigation showed tha t larvae of A. verticis burrow and inhabit the hyporheic biotope. Subs trate particle size was found to be a primary limiting factor in the m icrodistribution of the larvae. When homogeneous substrates (either fi ne, medium, or coarse gravel, or small or large pebbles) were provided , small, mid-sized, and large larvae significantly preferred coarse gr avel or small pebbles. Small larvae were better represented in coarse gravel, and large larvae were better represented in small pebbles. Ver tical distribution was deeper in coarse gravel than in medium gravel, and smaller larvae were generally found deeper than large larvae. In t he field, larvae occur in gravel or pebbles (excluding coarse sand or smaller particles) or mixed substrates, often at the interface of larg e rocks and finer substrates. Videomacroscopic examination also indica ted larvae to be interstitial dwellers. Although relatively crude burr owers, larvae do use their tusks to excavate substrate, and their gill s to generate interstitial current. We distinguish the fossorial behav ior of Anthopotamus from most other ephemeroid mayflies because tube b urrows are not formed. Minimum-sized interstices may be required for f ilter feeding and/or adequate ventilation, and may explain a deeper pe netration of smaller larvae in finer substrates.