Morphogenesis of a unique pseudourostylid ciliate, Trichototaxis songi (Ciliophora, Urostylida)
Introduction
Trichototaxis songi Chen et al., 2007, which was originally isolated from a freshwater pond in Hangzhou, China, is characterised by having a variable number of marginal cirral rows (Chen et al. 2007). The number of marginal rows is a key character in the systematics of urostylids. Indeed, the main difference between the urostylid families Pseudourostylidae and Pseudokeronopsidae is the presence of multiple marginal rows in the former compared with single right and left rows in the latter. In his taxonomic revision of the Urostyloidea, Berger (2006) assigned the genus Trichototaxis Stokes, 1891 to the Pseudourostylidae, a decision accepted by Lynn (2008) who misspelled it ‘Trichotaxis’. However, Chen et al. (2007) provided an improved genus diagnosis and considered Trichototaxis to be a member of the Urostylidae.
According to Berger (2006), the Urostylidae, the frontal cirri of which are arranged in a monocorona, bicorona, or tricorona, includes 11 genera. Subsequently, four additional genera have been reported: Apokeronopsis Shao et al., 2007, Heterokeronopsis Pan et al., 2013, Nothoholosticha Li et al., 2009, and Apoholosticha Fan et al., 2014. Of these 15 genera, 10 have been investigated morphogenetically, namely Pseudourostyla, Thigmokeronopsis, Apokeronopsis, Pseudokeronopsis, Uroleptopsis (Uroleptopsis), Uroleptopsis (Plesiouroleptopsis), Heterokeronopsis, Nothoholosticha, Apoholosticha, Keronella, and Urostyla. Morphogenesis in all of these genera is fundamentally the same, albeit with variations due to the presence of various special structures (Berger, 2004, Berger, 2006, Chen et al., 2010, Chen et al., 2011, Fan et al., 2014, Li et al., 2009, Mihailowitsch and Wilbert, 1990, Pan et al., 2013, Shao et al., 2007a, Wiackowski, 1985, Wicklow, 1981). Morphogenesis in Trichototaxis, however, has yet to be investigated.
In 1999, a population of Trichototaxis songi was isolated from a freshwater puddle in Zibo in eastern China, allowing its divisional morphogenesis to be investigated for the first time. These new data will help to improve knowledge and understanding of the variability in the patterns of development for multiple marginal rows during morphogenesis, as well as the systematics both of the genus Trichototaxis and of the families Pseudourostylidae and Pseudokeronopsidae.
Section snippets
Sampling and cultivation
Trichototaxis songi was isolated from a freshwater fish-farming pond (1–1.5 m deep) in the west suburb of the city of Zibo (lat. 36°48′ N, long. 118°2′ E), East China, on 15 August 1999 when the water temperature was 22 °C and the pH 6.9. Later this pond dried up and has become a residential area in 2002, that is, the population is very likely extinct. Isolated specimens were maintained as non-clonal cultures in Petri dishes with filtered water from the original sample site (Lv et al. 2013). Rice
Morphology of the Zibo population of Trichototaxis songi during interphase (Fig. 1A–C; Table 1)
Body basically long elliptical in outline, right and left margin slightly convex, and both ends rounded. Cortex reddish due to brick-red pigment granules that are grouped along the cirral rows and dorsal kineties. Numerous (more than 150) macronuclear nodules, each claviform to ovoid in shape, distributed throughout the cell. Locomotion by slowly crawling on substrate or swimming in water when disturbed. Adoral zone about 25–33% of body length, consisting of 36–73 (53 on average) membranelles.
Identification of the Zibo population
Trichototaxis songi was first described from a population isolated at Hangzhou, China (Chen et al. 2007). The Zibo population investigated here closely resembles the Hangzhou population apart from slight differences in the numbers of frontoterminal, buccal, midventral and bicoronal cirri (Table 1). We believe that these differences are environment-, population-, or observer-dependent and therefore not significant for species separation. Furthermore, the red blood cell-shaped granules described
Acknowledgements
This work was supported by the Natural Science Foundation of China (project numbers: 31372148, 31172041) and the Fundamental Research Funds for the Central Universities.
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