Divisional morphogenesis in the marine ciliate, Hemigastrostyla enigmatica (Dragesco & Dragesco-Kernéis, 1986) and redefinition of the genus Hemigastrostyla Song & Wilbert, 1997 (Protozoa, Ciliophora)

Abstract

Morphogenetic events during the division of the marine hypotrichous ciliate, Hemigastrostyla enigmatica (Dragesco & Dragesco-Kernéis, 1986) Song & Wilbert, 1997 are described. The morphogenesis is characterized by:

(1) 5 frontoventral-transverse cirral anlagen develop into 8 frontal, 5 ventral and 5 transverse cirri after Oxytricha-pattern;

(2) there may be 6 FVT-anlagen in some individuals giving rise to more cirri which, however, will be resorbed after division;

(3) anlage of the right marginal row at least in the opisthe occurs de novo right to the parental structures instead of within them;

(4) according to the origin, the two extra ventral cirri right to transverse ones are not ventral or transverse cirri, which are from the retained old structure;

(5) dorsal kineties originate from one group of DK-anlagen in both dividers with, very uniquely, an additional fragmentation of DK1, and

(6) oral primordia will be formed in both dividing parts, from which the newly-built membranelles in the proter replace the posterior part of the parental AZM with a particular 'piecing together’ mode.

Some features during the morphogenesis (e.g. variable number of cirral anlagen, presence of primary primordia, the mode of rebuilding of the proter's adoral zone of membranelles, origin of dorsal kineties and caudal cirri etc.) indicate that the genus Hemigastrostyla might present a intermediate form between oxytrichids and other related higher taxa. Based on our new observations, an improved diagnosis for genus Hemigastrostyla is given: marine or brackish water Oxytrichidae with slightly to conspicuously cephalized body shape; mostly 8–10 frontal, 5 ventral, 5 transverse and two to several extra ventral cirri to the right of the transverse ones, which are from the retained parental structure; caudal cirri present.