Mann Kyoon Shin

The morphology, the infraciliature, some stages of cell division and physiological reorganization, and the SSU rRNA gene sequence of the little-known marine 18-cirri hypotrich Tachysoma rigescens (Kahl, 1932) Borror, 1972 [basionym Oxytricha (Tachysoma) rigescens], isolated from mariculture waters near Qingdao, China, were investigated. This rare species is characterized, inter alia, by narrowly spaced, small, colourless cortical granules and several conspicuous ring-shaped structures in the cytoplasm. The caudal cirri and the simple dorsal kinety pattern (three bipolar kineties) are probably plesiomorphic traits within the Hypotricha, the composition of the adoral zone of the proter from new and parental membranelles, as well as the presence of two ‘extra’ cirri behind the right marginal row strongly suggest a misclassification in Tachysoma. The SSU rRNA gene sequence data indicate that T. rigescens branches off rather basally in the Hypotricha tree, which supports the hypothesis that the 18-cirri pattern occurred very early, probably already in the last common ancestor of the Hypotricha. A detailed survey of the early branching 18-cirri hypotrichs and similar taxa (e.g. Trachelostyla pediculiformis, Hemigastrostyla enigmatica, Protogastrostyla pulchra) reveals that for T. rigescens a new genus (Apogastrostyla gen. nov.) has to be established, because there are important differences, inter alia, in the dorsal infraciliature. Besides the type species, A. rigescens comb. nov., which seems to be confined to the northern hemisphere according to the sparse faunistic data, a second marine species, A. szaboi comb. nov. (basionym Hemigastrostyla szaboi), so far only twice recorded from the Antarctic region, can be included. The Chinese population is fixed as neotype to define the species objectively, because no type material of A. rigescens is present and the original type locality is not known. The species name Tachysoma multinucleate is emended: Tachysoma multinucleatum nom. corr.

The largest known Aspidisca species, A. magna Kahl, 1932, was found from coastal waters near Qingdao (Tsingtao), northern China, and investigated using both the “wet” silver nitrate and protargol staining method. Based on the living observation and impregnated individuals, improved diagnosis and morphometric data are provided. As an additional contribution, the morphogenesis in Aspidisca magna during binary fission was revealed and summarized as follows: 1) the parental adoral zone of membranelles and paroral membranęare retained by the proter; 2) the oral primordium of the opisthe develops hypoapokinetally behind the posterior part of the adoral zone of membranelles; 3) five frontoventral-transverse cirral anlagen are formed de novo, initially as primary primordia, and develop into 3:3:2:2:1 cirri from left to right, respectively in both dividers; 4) the leftmost frontoventral cirrus is generated from an independently formed cirral anlage in both dividers. In the present work, Chinese and Korean populations of A. leptaspis Fresenius, 1865 were investigated respectively to support the importance of living characteristics in identification of Aspidisca species. The isolation of A. magna and A. leptaspis from other congeners are also firmly demonstrated by the SSU rRNA gene sequence alignments.

We isolated a relatively unknown haptorian ciliate, Trachelophyllum brachypharynx, in brackish water from the mouth of the Taehwa River, South Korea. The morphology of this isolate was studied using in vivo observation and protargol impregnation, and its evolutionary history was revealed by phylogenetic analysis of the 18S rRNA gene. The main features of T. brachypharynx include (i) a very narrowly fusiform and slightly contractile body about 380 × 40 μm in size; (ii) two ellipsoidal macronuclear nodules typically connected by a fine strand; (iii) a single terminal contractile vacuole; (iv) filiform extrusomes that are typically 30 µm long; (v) an average of 24 ciliary rows, with two of them anteriorly differentiated into an isostichad dikinetidal dorsal brush; and (vi) hat-shaped lepidosomes. Based on the 18S rRNA gene phylogeny, T. brachypharynx clustered together withTrachelophyllum sp. within the order Spathidiida. Furthermore, phylogenetic trees and networks indicate some members from the genera Enchelyodon and Spathidium as the nearest relatives of trachelophyllids. Therefore, based on the present molecular and comparative-morphological analyses, we suggested a hypothesis explaining how trachelophyllids may have evolved from a spathidiid-like ancestor via an enchelyodonid-like stage.

Pleurostomatids are raptorial ciliates that form a very distinct group within the Haptoria. Traditionally, the order Pleurostomatida was divided into two families: the Amphileptidae with two perioral kineties and a suture formed by the right side ciliary rows, and the Litonotidae with three perioral kineties and without suture. However, molecular phylogenies depicted the “traditional” Amphileptidae as a paraphyletic assemblage nesting also the Litonotidae. To overcome this problem we have analyzed genealogy of pleurostomatids using morphological data and 18S rRNA gene sequences, including newly sequenced genera Acineria and Kentrophyllum. Specifically, we have combined a morphological and molecular approach and have used also some other phylogenetic tools such as phylogenetic networks, split spectrum analysis, quartet mapping as well as the likelihood method of tracing history of morphological characters. These analyses show that: (1) there are not two but three distinct pleurostomatid lineages – Epiphyllidae fam. nov., Amphileptidae and Litonotidae; (2) epiphyllids (Epiphyllum + Kentrophyllum) represent a basal pleurostomatid group which is defined by two perioral kineties, by the presence of a suture on both the right and the left side of the body, by the loss of the oral bulge extrusomes, and by the extrusome fringe extending all around the body except for the oral region; (3) the families Amphileptidae and Litonotidae are monophyletic each, and represent sister groups; (4) Acineria belongs to the Litonotidae, as already indicated by morphological data; (5) Loxophyllum is a monophyletic and crown genus of the Litonotidae; and (6) Litonotus is paraphyletic, which could be very likely caused by a rapid radiation event that did not allow primary nucleotide homologies to be fixed.