The enigmatic kinorhynch Cateria styx Gerlach, 1956 – A sticky son of a beach

Abstract

Since its discovery in the mid-1950'ies, Cateria has been an enigmatic kinorhynch genus due to its aberrant worm-like shape and extremely thin cuticle. However, the rare occurrence of the species, only found in sandy intertidal habitats, and the poor preservation of the type material have hampered detailed studies of the genus over time. Now, sixty years after the original description of Cateria styx, we present an extensive morphological and functional study based on new material collected from its type locality in Macaé, Brazil. We combine live observations with detailed scanning electron microscopy data, new light microscopy material, confocal laser scanning microscopy and three-dimensional rendering. These observations show that C. styx displays a complex array of cuticular structures (spines, spinoscalids and extraordinarily complex cuticular ornamentation) that we interpret to be adaptations for mechanical adhesion, through friction and interlocking, in an interstitial habitat; the enigmatic dorsal organ, is a hydrostatic structure which function is inferred to be adhesive. Additional morphological traits in C. styx include: extremely elongated primary spinoscalids that cannot be completely retracted in the trunk; a reduced number of spinoscalids; sixteen elongated hairy patches in the introvert; fifteen trichoscalids that vary in length; the absence of a neck; dorsal spines being alternatingly displaced to either left or right side paradorsal positions; and high intraspecific variation in the number and position of glandular openings in the trunk.