Cuticle structure and systematics of the Macrobiotidae (Tardigrada, Eutardigrada)

The cuticle of tardigrades is characterized by three main layers: epicuticl e, intracuticle and procuticle. Pillars are present in the epicuticle of al most all heterotardigrades, but these structures are also known in a few sp ecies of eutardigrades. The apparent heterogeneity of the cuticular ultrast ructure in several species of the Macrobiotidae (Eutardigrada) prompted us to analyse the structure of the cuticle in this family. Eleven species in s everal genera were investigated with light and/or electron microscopy. All the species of the genera Murrayon and Dactylobiotus showed pillars in the epicuticle, whereas the examined species of Macrobiotus, Richtersius and Xe robiotus completely lacked pillars. Therefore, in the Macrobiotidae, in con trast to what appears with light microscopy, the cuticle is homogeneous wit hin each genus examined at the electron microscopic level. Considering the absence of pillars in the Macrobiotidae a synapomorphy, we propose the erec tion of two new subfamilies. Macrobiotinae subfam. n. is characterized by t he absence of pillars in the epicuticular layer and includes, in addition t o the genera Macrobiotus, Xerobiotus and Richtersius, the genera Pseudohexa podibius, Adorybiotus, and probably also Minibiotus, Calcarobiotus and Pseu dodiphascon. Murrayinae subfam. n. is characterized by the presence of pill ars in the epicuticular layer and includes the genera n Murrayon, Dactylobi otus and, probably, Macroversum.