A morphometric diagnosis using continuous characters of Pinnunavis edkuensis, sp. nov. (Bacillariophyta: Bacillariophyceae), a brackish-marine species from Egypt

Abstract

Pinnunavis edkuensis is reported as a new diatom species from Egypt from brackish and marine habitats. Its description and diagnoses focus on 12 continuous morphological characters: valve breadth, valve mantle shape and surface area, axial-central area shape and surface area, axial area breadth, distal and proximal interstriae distances, striae slopes, magnitude and position of maximal slope along a semivalve transect, and inter-raphe distance. These characters are considered along their ontogenetic trajectories, using a size vector, by means of regression analyses. Shape was assessed using geometric morphometric methods. Diagnostic comparisons of P. edkuensis were made with P. yarrensis, for which a lectotype was chosen and Grunow’s unpublished description and drawings presented, and P. zalatii, a new name replacing the illegitimate name, Navicula aegyptiaca. P. edkuensis was demonstrated to be a distinct group compared to these two similar species using 11 of the 12 characters. The diagnoses emphasize species recognition by means of anova, regression and randomization analyses and specimen determination primarily by means of regression-based prediction intervals. Additional comments are made on the statistical nature of gaps associated with characters described by discrete or continuous variables, the importance of reporting sample sizes as part of diatom diagnoses and other comparisons, and the role of size in specimen comparability and taxon identification. The generic distinctness of Pinnunavis and Pinnularia is discussed based on a preliminary cladistic analysis of morphological characters.

Morphometric Asymmetry of Frustule Outlines in the Pennate Diatom Luticola poulickovae (Bacillariophyceae)

“…Vegetative cells that then begin a new cycle again are in the upper size range of the species-specific interval [16]. Size reduction is typically accompanied by a change in the shape of the frustules [17][18][19][20], which leads to pronounced morphological allometry, a process typical of nearly every diatom population in natural habitats or cultured strains. Pappas et al [19] recently reported that variation in the empirical morphospace of most pennate diatom species relates to allometry as a result of the size reduction that occurs over successive vegetative cell divisions.…”

Quantitative comparison of taxa and taxon concepts in the diatom genus Fragilariopsis: a case study on using slide scanning, multiexpert image annotation, and image analysis in taxonomy1

“…This observation is not surprising, since increasing sample sizes (as well as increasing habitat diversity) are expected to lead to broader estimates of sample ranges (Edgar et al. ). Some participants (especially from the novice group) reported that if a valve with dimensions substantially outside the ranges given in the literature for a particular species was encountered, they tended to avoid labeling it as that species.…”

“…This was not by mistake, as some participants explicitly reported that they interpreted morphometric ranges regularly provided in taxonomic descriptions (in this case, for valve length, width, stria density) with caution, knowing that they rarely cover the full range of variation occurring in nature (Crosta 2009a, Shukla et al 2013, Kloster et al 2017). This observation is not surprising, since increasing sample sizes (as well as increasing habitat diversity) are expected to lead to broader estimates of sample ranges (Edgar et al 2015). Some participants (especially from the novice group) reported that if a valve with dimensions substantially outside the ranges given in the literature for a particular species was encountered, they tended to avoid labeling it as that species.…”

Quantitative Morphometric Analysis of Morphologically Similar Species of Fragilaria (Fragilariaceae, Bacillariophyta) Allows Detection of Non-Indigenous Taxa: A Case Study from Lake Ladoga (North of European Russia)

“…Despite significant changes in valve outline during diatom morphogenesis, an overall specific valve shape for each species is retained throughout the size-diminution series [30]. Therefore, ontogenetic-allometric trajectories visualizing the variation of valve shape with size can be used for the morphological characterization of diatom species [20,31,32]. The main idea of applying allometric regression lines for species recognition is that the shape of different specimens is easier to compare when the specimens all have the same size [32].…”