Morphological and molecular reinvestigation of acanthoecid species I. – Enibas urnula (Thomsen, 1973) comb. nov. (= Stephanoeca urnula Thomsen, 1973)

In the course of the last decades, several acanthoecid choanoflagellates have been assigned to the tectiform reproducing genus Stephanoeca based on lorica morphological comparability. The recent description of a Stephanoeca-like nudiform genus, Enibas Schiwitza, Arndt and Nitsche, 2019, has emphasized the possibility that some species assigned to Stephanoeca (based solely on lorica morphological features) might in the end have to be relegated to other genera. Stephanoeca urnula Thomsen, 1973, shows a striking morphological resemblance to E. thessalia Schiwitza and Nitsche, 2020. Also, the inability to document from microscopy any bundles of supernumerary costal strips in the collar region of this species, makes it an obvious Stephanoeca outcast candidate. We have revisited the S. urnula type locality and established this species in crude culture. A detailed SEM morphological analysis of cultured specimens, and a molecular analysis of the SSU and LSU rRNA, has unveiled its undisputed affiliation to the nudiform genus Enibas. Here, we redescribe S. urnula Thomsen, 1973 as E. urnula (Thomsen, 1973) comb. nov. Based on microscopical examinations of species of Stephanoeca and Enibas we have been able to pinpoint anterior lorica chamber construction details, that in the future renders possible a morphological distinction between the two genera.