Identification of three highly confused marine Loxophyllum (Ciliophora: Pleurostomatida) with a key to seven congeners from the China Sea.

Three highly confused Loxophyllum helus-like morphotypes (i.e. Loxophyllum rostratum Cohn, 1866, Loxophyllum sinicum n. sp., and Loxophyllum simplex Kahl, 1933) found in mariculture waters near the coast of Qingdao, China, were investigated with emphasis on their live morphology and infraciliature. Comparative descriptions of these three organisms are presented and synonyms are critically discussed. The validity of L. sinicum n. sp. is confirmed mainly by the combination of the distribution of extrusomes, features of general living morphology, morphometric data, and the characters of the somatic ciliature. Two previously reported organisms under the name of L. helus by Dragesco (1966, variety a) and by Dragesco and Dragesco-Kernéis (1986) are discussed and are believed to be synonyms of L. sinicum. Furthermore, two isolates described by Dragesco (1960) and Ozaki and Yagiu (1943) under the name of L. helus are very likely, in our opinion, misidentifications, and might be two unknown forms. In the light of the current study, a key is presented to the seven clearly defined marine Loxophyllum species found in the coastal areas of north China Sea.