MORE ON THEORETICAL MORPHOSPACE AND ITS RELATION TO FRESHWATER GOMPHONEMOID-CYMBELLOID DIATOM (BACILLARIOPHYTA) LINEAGES

Abstract

All forms from hypothesized gomphonemoid-cymbelloid lineages were constructed using three-dimensional (3D) parametric equations with the same boundary intervals for all forms. To construct a theoretical morphospace, the absolute value of the Riemann sum of differences between pairs of forms in terms of surfaces in the x-, y- and z-directions was determined and plotted in 3D space. In general, naviculoid forms occupied the lowest valued morphospace, and cymbelloid and gomphonemoid forms occupied different higher valued morphospaces. In particular, Anomoeoneis, Brebissonia and Placoneis were basal to cymbelloid and gomphonemoid forms. Brebissonia was found to be more closely related to gomphonemoid forms, and Placoneis was found to be more closely related to cymbelloid forms. Reimeria was found to be in lower valued morphospace than other cymbelloid forms, including Encyonema. Didymosphenia was found to be more closely associated with cymbelloid morphospace. Gomphocymbelloid forms were more closely associated with gomphonemoid forms. These results are complementary to the previous study and mostly supported Kociolek and Stoermer’s cladistic analysis of gomphonemoid-cymbelloid lineages. In addition, some ideas concerning evolutionary pathways and ontogeny with respect to theoretical morphospaces were explored.