Ultrastructure of CaCO3 deposits of terrestrial isopods (Crustacea, Oniscidea)

 The ultrastructure of the sternal CaCO₃ deposits of 3 species of the Diplochaeta and 15 of the Crinochaeta was investigated by means of scanning electron microscopy of fractured surfaces. In the Diplochaeta Li-gia italica and L. oceanica, the deposits consist exclusively of individual spherules with diameters between 0.2 and 1.4 μm. No material was observed within the spaces between the spherules. In Ligidium hypnorum, two structurally distinct regions exist. A proximal layer resembling the deposit of Ligia italica and L. oceanica and a distal layer in which the spherules appear to be fused with each other. In the species of the Crinochaeta, the CaCO₃ deposits comprise a spherular region which resembles the deposits of Ligidium hypnorum, and a homogeneous layer located between the spherular part of the deposit and the hypodermal cell layer. In some species the diameters of the spherules may be up to 3.1 μm. In the homogeneous layer and the distal spherular layer more calcium per volume can be stored than in the proximal spherular layer in which the spaces between the spherules are devoid of CaCO₃. This suggests that the multiple layered deposits are an adaptation to terrestrial life, as a consequence of the need for increased resorption of cuticular calcium. Accepted: 7 January 1997