The shell wall ultrastructure, collars, wrinkle layer, siphuncle morphology, and the ultrastructure of the connecting rings are described in the Aptian (Early Cretaceous) lytoceratid Eogaudryceras Spath from Adygeya, north-western Caucasus, Russia. The collars are pronounced and number 4-5 per shell whorl. They enlarged the shell surface and increased the buoyancy and mechanical shell strength. The siphuncular tube consists of calcareous prochoanitic septal necks and cuffs that became proportionally longer during the ontogeny, and comparatively short, organic (possibly glycoprotein) connecting rings that are phosphatized and consist of aggregates of small globular particles. There is some evidence of a porous structure, which may have provided a higher permeability of the connecting rings and increased the gas/liquid exchange between the siphuncle and shell chambers for vertical migrations. The morphological and structural shell characteristics indicate that the shell design was adapted for pelagic, probably deep-water habitat, and vertical, possibly diurnal, migrations.