ECOLOGY AND TAXONOMY OF Holimeda 69 



Hori, 1974; Calvert et al., 1976), a genus not discussed by Feldmann 

 (1946). It seems likely that at least small grains of starch in chloroplasts 

 may be fairly commonplace throughout the heteroplastic green algae, 

 that their number or size may vary with the time of day, although not 

 invariably (see Calvert et al. (1976) for behaviour in Caulerpa sp.), and 

 that the real point of emphasis, as well as of interest, should be in the 

 presence or absence of a separate starch-storing body (the amyloplast). 

 The Caulerpa— Halimeda-Udotea algal series, then, has evolved a separate 

 starch-storing plastid, whereas the C odium- Derhesia series does not use 

 this starch storage plan, at least to any great extent. 



(d) Proposed scheme for classification ofHalimedsi. Although filament- 

 wall chemistry and life-history data do not satisfactorily delimit orders 

 among the C odium- Derhesia group of algae at this time, there is more 

 support for a separation of the Caulerpa-Halimeda-Udotea group from 

 the C odium- Derhesia group. The data are limited to examination of the 

 commoner genera and species, but the members of the Caulerpa- 

 Halim^eda-Udotea group examined, have: 



a separate starch-storing body (amyloplast) ; 



xylan in their filament walls, at least those of the photosyn- 

 thetic portions of the plant (although not detected in walls of 

 cultured Caulerpa ambigua Okamura ( = C. vickersiae Borgesen) 

 which was also morphologically unusual in lacking pinnae (Huizing 

 etal, 1979)); 



a life-history that involves the death of the alga (or the part of 

 it involved) after sexual reproduction. 



A fourth characteristic is valid for many of the taxa : 



the presence of chloroplast lamellar systems. 



To reflect these differences I suggest the recognition, or retention, of 

 a system of either four or two orders (depending on the classification 

 used) : 



Derbesiales (containing Codium, Bryopsis and Derhesia as well 

 as related genera), and 



Caulerpales (the Caulerpa-Halimeda-Udotea series), with the 

 continued use or acceptance, for the other genera as required, of the 

 orders 



Dichotomosiphonales 



Phyllosiphonales (or Ostreobiales if Phyllosiphon is transferred 

 to Xanthophyta). 



