Morphological redescription and neotypification of the marine ciliate, Amphisiella marioni Gourret & Roeser, 1888 (Ciliophora: Hypotrichida), a poorly known form misidentified for a long time.

The "well-known" marine hypotrichous ciliate, Amphisiella marioni Gourret & Roeser, 1888 has been repeatedly misidentified for over a century, which has led to great confusion in the species identification. Based on a population collected from mariculture water in Qingdao (Tsingtao), north China, the morphology and infraciliature were investigated using live observations and the protargol impregnation method. The Chinese population corresponds perfectly with the original description by Gourret and Roeser (1888). As the type species of Amphisiella, its morphological characteristics include: an elongated body about 90-150 microm long in vivo; with grouped cortical granules arranged in irregular rows throughout the whole body; a contractile vacuole located slightly behind mid-body; adoral zone of membranelles slightly bipartite in structure with the anterior part ventrally located; amphisiellid median cirral row (ACR) extending to the level of the transverse cirri (TC); about eight frontal cirri left of the ACR; closely spaced marginal rows, displaced inwards, each with about 32 cirri; six TC arranged in a V-shape; no caudal cirrus; five to six dorsal kineties; and typically two macronuclei. We conclude that the populations described by Mansfeld (1923) and Wicklow (1982), respectively, were misidentified. To clarify the taxonomic status of this species, the population from the northern Chinese coast of the Yellow Sea is designated as a neotype.