Surface structure of aesthetascs in Cryptoniscina (Isopoda Epicaridea)

Abstract

Abstract By means of scanning and transmission electron microscopy the surface structure of the antennular aesthetascs was studied in specimens from all 7 families of the Cryptoniscina. A detailed description is given of the treatment of this material for the scanning technique. The number of aesthetascs seems to be constant within the species, but a variation between different families is found, the extremes being about 14 (Cabiropsidae) and approximately 100 (Liriopsidae). The occurrence of aesthetascs (generally 2) on the lateral antennular flagellum is probably a general feature of the Gryptoniscina, and there is little doubt that this flagellum is homologous with the lateral antennular ramus of e.g. decapods. The general appearance of the aesthetascs is that of a long and very narrow cylinder (cross section about 1.3 μ). The proximal one-third has a smooth external surface while the distal two-thirds are marked by a longitudinal striation of the cuticle. The distal one-third is characterized by nodular swellings. The thickness of the cuticle, the appearance of striations and nodes, and also the number and density of nodes varies between different species. However, different types of nodes are also found on the same aesthetasc. The main function of the abovementioned cuticular surface structures is probably a supporting one, rather than one in which an increase in surface area is of importance for chemoreception.