Basicladia chelonum (Collins) W.E. Hoffmann et Tilden (Chlorophyta, Cladophorophyceae) from Cuba (Caribbean): new observation of the ultrastructure of its vegetative cells

Abstract

Basicladia chelonum (Collins) W.E. Hoffmann and Tilden (1930) principally known from North America and Hawaii was recently (2004) found in Cuba (Caribbean) from artificial pool growing on shells of musk turtles (Trachemys decussata Gray). Specimens collected in Cuba were subjected to detailed examinations also using a transmission electron microscope. On one hand, these studies confirmed many features of this species previously described by earlier authors in the specimens from Texas. On the other hand, the present studies revealed structures unknown so far (pyrenoid structure), which allowed for new analysis of this species. These investigations also have shown that Basicladia chelonum exhibits close similarity to the genus Cladophora and other representatives of the class Cladophorophyceae. The similarities include : siphonocladous level of organization of thallus, numerous chloroplasts forming a network and other structures. Conversely, the pyrenoid in vegetative cells of Basicladia chelonum distinguishes it markedly from representatives of the genus Cladophora, which have bilenticular pyrenoids divided into two hemispheres by a single thylakoids and each hemisphere is covered by a bowlshaped starch grain (Van Hoek et al. 1995). Since in Cladophora the ultrastructure of the pyrenoid is highly constant and characteristic, this contrasts with the genus Basicladia and, therefore, more firmly establishes position of the latter as an independent unit within Cladophorophyceae.