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 Maca e, 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.

Myoanatomy of three aberrant kinorhynch species: similar but different?

“…Ten specimens of F. kalenesos fixed in 4% PFA were dehydrated through a water-ethanol series, and transferred to acetone through an ethanol-acetone series, critical point dried, mounted on aluminium stubs, sputter coated with a mix of platinum-palladium and examined under a JEOL JSM-6335F Field Emission SEM. SEM specimens of Z. yong and C. styx from Altenburger et al (2015) and Herranz et al (2019) stored in MVS' collection were re-examined. Additional SEM photos of Z. yong were kindly provided by Andreas Altenburger.…”

“…Kinorhynchs, commonly named mud dragons, have a quite conserved body plan with three well differentiated regions: a head, a neck, and a segmented trunk. However, some genera with a characteristic worm-like appearance, exhibit significant modifications in one or more of these regions including: (i) introverts with reduced number of scalids; (ii) extremely long and flexible primary spinoscalids; (iii) neck with poorly developed or lacking placids; (iv) slender trunk with very thin cuticle, and (v) less distinct external segmentation (Dal Zotto et al 2013;Neuhaus and Kegel 2015;Herranz et al 2019;Yamasaki 2019).…”

“…The first aberrant, worm-like kinorhynch species described was Cateria styx Gerlach, 1956, collected intertidally from a sandy beach in Macaé, Brazil (Gerlach 1956). C. styx possesses several unusual and distinct characters including a very thin cuticle, a different arrangement of tergal and sternal plates in the trunk, neck without differentiated placids, introvert modifications, and a unique dorsal organ (Gerlach 1956;Herranz et al 2019). The genus accommodates one additional species, C. gerlachi Higgins, 1968, that also lives intertidally and is described from a sandy beach in Waltair, India (Higgins 1968).…”

“…Most studies on aberrant kinorhynchs have focused on their taxonomy, external morphology, phylogeny and ecology (Dal Zotto et al 2013;Neuhaus and Kegel 2015;Sørensen et al 2015;Herranz et al 2019;Lopes Mello et al 2019;Yamasaki 2019;Rucci et al 2020), but little is known about their internal morphology. Only some aspects of Cateria styx and two other Zelinkaderes species (Zelinkaderes brightae Sørensen et al, 2007 and Zelinkaderes floridensis Higgins, 1990) have been studied using confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) (Neuhaus 1994;Herranz et al 2013Herranz et al , 2019.…”

“…Kinorhynchs with well-defined outer trunk segmentation also have correlating and segmentally arranged organ systems such as the musculature or the nervous system (Nebelsick 1993;Müller and Schmidt-Rhaesa 2003;Herranz et al 2013Herranz et al , 2014Herranz et al , 2019Herranz et al , 2020Altenburger 2016). However, it is still unclear how the internal morphology is organized in worm-like kinorhynchs with a thin cuticle and poorly differentiated trunk segments.…”