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Abstract
Morphology and divisional morphogenesis of the hypotrich ciliate Apoamphisiella vernalis are investigated based on two populations from Brazil. Typical specimens of A. vernalis replicates its ventral ciliature from six fronto-ventral-transverse (FVT) anlagen independently formed for proter and opisthe, plus one or more short anlagen located between IV and V, which form surplus transverse cirri. Dorsal morphogenesis occurs as in typical oxytrichid dorsomarginalians, viz., with formation of three anlagen and fragmentation of the rightmost one. Dorsomarginal kineties are formed near anterior end of right marginal cirral row anlagen. Various anomalous specimens exhibiting more than two long ventral rows were found, which are explained by increasing the number of FVT anlagen and/or the number of cirri produced by anlagen. Comparative ontogeny and phylogenetic analyses based on the 18S rDNA reveal that Apoamphisiella vernalis is closely affine to North American and European strains of the Paraurostyla weissei complex. Their reduced genetic distances and conspicuous morphological variability show that both genera can overlap, which implies the necessity of re-evaluating the contextual relevance of some morphological characters commonly used for genus-level separation within hypotrich taxa.
Highlights
The Hypotricha Stein, 1859 (= Stichotrichia Small & Lynn, 1985) is a relatively ubiquitous group of ciliates characterized by having, inter alia, a flat body with well differentiated ventral and dorsal regions, ventral ciliature organized in clusters and/or rows of locomotory cirri, dorsal ciliature with sensory bristles, at least one left and one right marginal cirral rows, a polyhymenophore adoral zone of membranelles and two undulating membranes [1,2,3,4,5]
Intending to fill in a gap of the jigsaw puzzle of hypotrichs’ natural history, we investigate the morphology and ontogeny during divisional morphogenesis of Apoamphisiella Foissner, 1997, based on two Brazilian strains of A. vernalis (Stokes 1887) Berger 2006, and hypothesize its phylogenetic affinities from analyses of the 18S-rDNA
As pointed by Paiva et al [39], common taxonomic features related to body size and ciliary structures overlap among species of Apoamphisiella [67,68,69,70,71], the most stable characters being presence/absence and color of cortical granules, number of contractile vacuoles and presence/ absence of collecting canals
Summary
The Hypotricha Stein, 1859 (= Stichotrichia Small & Lynn, 1985) is a relatively ubiquitous group of ciliates characterized by having, inter alia, a flat body with well differentiated ventral and dorsal regions, ventral ciliature organized in clusters and/or rows of locomotory cirri, dorsal ciliature with sensory bristles, at least one left and one right marginal cirral rows, a polyhymenophore adoral zone of membranelles and two undulating membranes (paroral and endoral) [1,2,3,4,5]. Variations in the number, position and number of structures produced by different anlagen (= primordia), like fronto-ventral-transverse (FVT), marginal and dorsal anlagen, are responsible for archetypical ciliature elements, such as the amphisiellid rows, the midventral complex, the oxytrichid “18-FVT” cirral pattern, and the many dorsal bristle arrangements that can be observed among different groups Those are hitherto used for determination of hypotrich genera and species, and their miscellaneous suprageneric ranks [1,2,3,4, 17, 19, 24,25,26,27,28,29,30]. According to Jung et al [36], other possible explanations for the “difficult” systematics of hypotrichs may relate to misidentified sequences deposited in the NCBI/GenBank, inadequacy of methods, insufficient taxa sample and incorrect morphological concepts of taxonomic groups
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