An original respiratory structure in the xeric genus Periscyphis Gerstaecker, 1873 (Crustacea: Oniscidea: Eubelidae)

A detailed morphological description of the pleopodal lung in the xeric isopod genus Periscyphis Gerstaecker, 1873 is presented. The lung is characterized by: a) a single spiracle in the form of a short narrow fissure situated on the posterior margin of the most external part of the pleopodal exopod where the distance between the margin of the appendage and its insertion into the body is minimal; b) the possibility, within certain limits, for the spiracle to close; c) the ansence of true respiratory area; d) a short tubular entrance channel;e) a sacciform atrium; f) the enourmous development of the mass of respiratory tubules which penetrate the body cavity and which, at least in P. ruficauda Budde-Lund, 1908, are distributed throughout the pleon and seventh perepnite. The latter characteristic constitutes the first, and for the moment only, documented case among the Oniscidea. The functional and adaptive value of the lung is discussed.