A developmental explanation for the Corallina- and Jania-types of surfaces in articulated coralline red algae (Corallinales, Rhodophyta)

Abstract

Thallus surface features associated with epithallial cells and trichocytes provide systematic characters useful for distinguishing some members of the tribes Janieae and Corallineae (Corallinales, Rhodophyta). Electron microscopical study of representatives of the genera Corallina, Jania, Haliptilon, and Cheilosporum suggests an anatomical basis for these character states. The C-type surface, which is the prevalent type in the subfamily Corallinoideae, is formed by filaments presenting apical (transverse) faces to the thallus surface. In contrast, the longitudinally elongate epithallial profiles and asymmetrical trichocyte bases characteristic of J-type surfaces are both manifestations of the same underlying structure: the more delicate J-type species present the longitudinal face of the filaments to the thallus surface. If these interpretations are correct, it should be possible to infer the surface type from the anatomical information; conversely, some basic anatomical information could be inferred from the surface type. Based on the anatomy of J. pusilla, a C-type surface was predicted and, upon examination, was found. A striking feature of the two species of Jania with a J-type surface was the absence of a layer of intercalary initial cells, a layer that in most coralline algae produces epithallial cells distally and cortex cells proximally. The absence of an initial cell layer may be part of the developmental program that results in a J-type surface. Parallels can be drawn to the anatomy of some nonarticulated species.