The biology of Haloniscus searlei Chilton, an oniscoid isopod living in Australian salt lakes

Abstract

The results of field and laboratory investigations concerning the biology of Haloniscus searlei Chilton (Crustacea: Isopoda: Oniscoidea) are reported and discussed. It occurs in Victoria, Tasmania, South Australia, and Western Australia, where, although belonging to the almost exclusively terrestrial Oniscidae, it lives only in inland salt lakes; from these it has been collected at salinities from 8 to 159‰.

Breeding females occur throughout the year, but are most abundant in summer. The life-cycle conforms to the typical isopodan pattern.

Laboratory investigations provided upper and lower L.D.₅₀ values for salinity with acclimation of 159 and < 1‰ and without acclimation of 118 and 4‰. In resistance to desiccation, H. searlei does not seem to be significantly different from terrestrial isopods, and in air its survival is a matter of hours. Its degree of cuticular impermeability places it between Oniscus and Porcellio in the following series of genera with increasing impermeability: Ligia < Philoscia < Oniscus < Haloniscus < Porcellio < Armadillidium. The pleopods display no modifications for terrestrial breathing.

The view that H. searlei is of terrestrial ancestry and that its forbears were physiologically preadapted for life in inland salt lakes is upheld.