ECOLOGY AND TAXONOMY OF Holimeda 15 



other components of the cytoplasm include both smooth and rough 

 endoplasmic reticulum, free ribosomes, Golgi bodies, microtubules, lipid 

 globules and mitochondria (Fabbri and Palandri, 1969; Wilbur et al., 

 1969; Palandri, 1972b; Borowitzka and Larkum, 1977). Palandri 

 (1972a) describes some unusual forms of mitochondria, and Borowitza 

 and Larkum (1977) report DNA-like fibrils in the matrix of giant 

 mitochondria occurring in the tips of young growing filaments. Palandri 

 (1972b) reported DNA in older mitochondria. 



3. Central vacuole 



The central vacuole in filaments of mature segments generally 

 occupies much of the filament system of the medulla and inner cortex 

 and contains a granular to somewhat fibrillar ground substance with a 

 variety of inclusions. Prominent among these are two distinctive types 

 of unidentified bodies (Wilbur et al., 1969). One is rounded or angu ar, 

 usually of high electron density (Figs 10, 55, 65, 66); the other is 

 spherical (Figs 56, 59, 66). Subsequently the spherical body has been 

 reported by other workers (Palandri, 1972b; Borowitzka and Larkum, 

 1977; Colombo and Orsenigo, 1977). Both unidentified structures may 

 also be associated with the cytoplasm. 



The spherical unidentified bodies are the larger, measuring 0*5-3 [zm 

 in diameter (Wilbur et al., 1969). They may consist mostly or entirely 

 of polysaccharide (Borowitzka and Larkum, 1977), and some may have 

 a hollow core. Texture is of non-oriented fibrillar substance throughout, 

 or of one or more zones of radially oriented material which at times 

 shows some resemblance to the ground substance of the central vacuole. 

 Sometimes the outer margin is barely distinguishable from surrounding 

 material, and in places fibrils extend from the spherical body to the 

 surrounding region. At other times tiny vesicles of varying sizes, 

 together with the electron-dense unidentified bodies, are closely associ- 

 ated with the outer boundary (personal observation). 



Similar spherical bodies and the considerably smaller electron- 

 dense unknowns have both been found in Penicillus (Turner and 

 Friedmann, 1974). Borowitzka and Larkum (1977) also report spherical 

 bodies for Udotea and the non-calcareous, siphonaceous genus Avrain- 

 villea. These workers (1977) did not find them in Caulerpa, nor were 

 they observed in another siphonalean non-calcareous genus Bryopsis, 

 for which Burr and West (1970, 1971a, b) report a "schizogenous body". 

 This unknown also seems to have some association with the fibrillar- 

 reticulum systems of the alga, but superficially is different from the 

 spherical body, and schizogenous bodies are proteinaceous. 



