Diophrys pauciciliata n. sp. (Ciliophora, Euplotida), a new marine spirotrich ciliate with highly static morphometrics.

A new marine ciliate was discovered from intertidal mudflat from South Korea. Based on the observation of living cells, protargol-impregnated specimens and SEM, we describe it as new species belonging to the genus Diophrys Dujardin, 1841, namely Diophrys pauciciliata n. sp. Its nuclear small subunit ribosomal RNA gene also supports the taxonomic assignment. Diophrys pauciciliata n. sp. is one of the smallest species in the genus. Besides, the bipartite adoral zone and oligomerized dorsal bristles easily discriminate the new species from other congeners. Interestingly, D. pauciciliata n. sp. showed highly static states in all morphometrics (<8.5 % of coefficient of variation) and in particular, the number of frontal adoral membranelles and the counts of dorsal ciliature (e.g., number of dorsal kineties and numbers of dikinetids within each kinety) are invariable. Considering morphometric data of previous studies in the genus Diophrys, the narrow range of character states is unexpected because cell length is usually positively correlated with the numbers of adoral membranelles and dorsal dikinetids.