A gutless wonder: First record of the remarkable acoel flatworm 'Wulguru cuspidata' in the Northern Territory

Abstract

This paper records the microscopic acoel flatworm 'Wulguru cuspidata' from the Northern Territory, in fact from the northern coastline of Australia, for the first time. Whilst being restricted to a narrow belt in the intertidal zone on sandy beaches fronting the ocean, this acoel can attain remarkably high densities. Despite the stressors it must experience in this habitat - of great fluctuations of temperature and salinity, and of toxic algal and bacterial blooms - it is present year round. Its behaviour, which is typical of acoels of the family Convolutidae, of moving to the surface of the substrate at low tide apparently to recharge its 'solar batteries' (i.e. provide light for its symbiotic microalgae) and of burying into the substrate at high tide, is described. Whilst this behaviour appears to be a response to a combination of tidal and daylight cycles, the biological clock causing it must be very complicated.