Morphological and molecular reinvestigation of acanthoecid species II. - Pseudostephanoeca paucicostata (Tong et al., 1998) gen. et comb. nov. (= Stephanoeca diplocostata var. paucicostata Throndsen, 1969) including also the description of Pseudostephanoeca quasicupula sp. nov. and Stephanoeca ellisfiordensis sp. nov.

The present study has revealed morphological differences of species assigned to the acanthoecid choanoflagellate genus Stephanoeca based on the relative position of transverse and longitudinal costae in the anterior lorica chamber. A detailed re-examination of published material of S. paucicostata Tong et al., 1998 combined with new data has shown that the species characteristic, a double transverse costa, is clearly located outside of the longitudinal costae excluding this taxon from an affiliation to Stephanoeca sensu stricto, confirmed also by molecular data of a clonal culture from Kos Islands, Greece. Two specimens of S. paucicostata with only a single, interiorly positioned transverse costa, namely from Marchant et al. (1987) and Nitsche et al. (2011) were erroneously assigned to this species. These facts have here led to the establishment of a new genus, Pseudostephanoeca with its type species P. paucicostata, and the description of S. ellisfiordensis for the two specimens mentioned above, corroborated by new material from Antarctica. In addition, two specimens previously assigned to S. cupula have been shown to share the core characteristic of Pseudostephanoeca with exteriorly positioned transverse elements. This has led (c) 2022 Elsevier GmbH. All rights reserved.