Discrepancy between morphological and molecular traits for species discrimination in the tintinnid ciliate Parafavella

Abstract

<em>Parafavella</em> spp. were collected during the cruise of the Korean research ice-breaker Araon 2012 in the North Pacific Ocean. The tintinnids are usually identified based on the morphology of loricae rather than infraciliatures. However, <em>Parafavella</em> which is one of the genera in tintinnids has a high variation on lorica morphology in size and shape that implies a existence of synonym or convergence on the lorica morphology. To clearly delineate the inter-specific boundary of <em>Parafavella</em>species, we analyzed the lorica morphology with their genetic traits. Based on the lorica, five species were identified as follows: <em>Parafavella denticulata</em>,<em> P. gigantea</em>,<em> P. hemifusus</em>,<em> P. parumdentata</em>, and <em>P. subrotundata</em>. With respect to the molecular trait, nuclear (SSU-LSU D2, ca. 3,000 bp) and mitochondiral (CO1, ca. 480 bp) genes were newly sequenced and analyzed. The nuclear gene sequences of all 5 morphospecies were completely identical each other whereas the CO1 sequence data was divided into 2 clades (<em>P. parumdentata</em> vs. <em> P. denticulata</em>-<em>P. gigantea-P. hemifusus-P. subrotundata</em>) with about 3% genetic dissimilarity between the groups. These two clades based on the molecular data were supported by morphological differences of width of lorica rather than the length in 5 species. However, it has been widely accepted that the length is a distinct diagnostic feature of<em> P. gigantea</em> discriminating from the other 4 congeners. To clarify this discrepancy in <em>Parafavella</em> species, we need further investigation on the infraciliatures with more genetic data.