Significance of the Nudiform and Tectiform Modes of Silica Deposition, Lorica Assembly and Cell Division in Choanoflagellates as Exemplified by Stephanoeca diplocostata and Enibas spp

• Published in: Protist 2022-12, Vol.173 (6), p.125923-125923, Article 125923
• Main Authors: Leadbeater, Barry S.C., Carr, Martin
• Format: Article
• Language: English
• Subjects: Acanthoecida; Cell Division; Choanoflagellata; Choanoflagellatea; Enibas evolution; Enibas lorica morphology; nudiform-tectiform relationship; Phylogeny; Silicon Dioxide; Stephanoeca diplocostata
• ISSN: 1434-4610; 1618-0941
• DOI: 10.1016/j.protis.2022.125923

•Complete silicon starvation of tectiform Stephanoeca diplocostata results in diagonal (nudiform) division.•Silicon-replenished S. diplocostata cells accumulate costal strips in a nudiform manner.•‘Nudiform loricae’ assembled on silicon-replenished cells display variations with respect to the transverse costae.•Newly identified nudiform genus Enibas possesses Stephanoeca-like loricae with similarities to nudiform loricae of S. diplocostata.•Suggested that morphological similarities together with recent phylogenetic analyses could imply Enibas species had a Stephanoeca-like ancestor. The deposition of silicified costal strips and lorica assembly in choanoflagellates is precisely linked to the cell cycle. A minority of species undergo nudiform division whereby a loricate cell divides to produce a naked daughter cell that deposits a set of costal strips and then assembles a lorica. Most species undergo tectiform division whereby a parent loricate cell produces a set of costal strips, divides and passes on the stored strips to a daughter cell that immediately assembles a lorica. Many phylogenetic analyses recover nudiform and tectiform species as sister-clades giving the impression that they are distinct evolutionary lineages. However, the tectiform species Stephanoeca diplocostata is capable of undergoing nudiform division and depositing costal strips and assembling a lorica with certain modifications in a nudiform manner. The recent discovery of a new genus, Enibas, comprising species with Stephanoeca-like loricae that undergo nudiform cell division and on phylogenetic analysis occur as a sister group to other nudiform species has drawn attention to whether there are also unique features in lorica construction. A range of Enibas loricae is illustrated and it appears that there are unique features which might be interpreted as being derived from a Stephanoeca-like ancestor.