PHYLOGENETIC SYSTEMATICS AS A GUIDE TO UNDERSTANDING FEATURES AND POTENTIAL MORPHOLOGICAL CHARACTERS OF THE CENTRIC DIATOM FAMILY THALASSIOSIRACEAE

Abstract

We list features of the siliceous cell wall which may be of use in the systematics of the Thalassiosiraceae. Many, but not all, of these features have been used in taxonomy of the members of the family. We have subdivided or redefined some previously used features such as “complex alveoli” into component parts. Discussion for potential characters are based on first principles of phylogenetic systematics rather than on agreement with current or desired taxonomic results. Features are considered as potential homologous characters if they share some degree of similarity and can be argued to be discretely heritable. The resultant list is large (over 80 features), but by no means complete because many details of Thalassiosiraceae frustule morphology remain unreported and unobserved. In fact, one of our objectives is to encourage microscopists to give more attention to the girdle bands and to better resolve so-called “minutiae” such as fultoportule cowlings (a new term defined and illustrated here).