ECOLOGY AND TAXONOMY OF Holimeda 141 



distinguished macroscopically by its trapezoidal-shaped segments which 

 are often somewhat greenish on drying. Thalh oi discoidea often possess 

 relatively large discoidal segments which dry to a brownish colour. The 

 segments of taenicola also appear to be somewhat more heavily calcified 

 than those of discoidea. 



Microscopically it also shows resemblances to discoidea, with the 

 rather characteristically expanded utricles of the innermost, usually 

 tertiary, layer of the cortex, although somewhat smaller in average 

 diameter, suggesting the secondary utricles of discoidea. In taenicola 

 these utricles often support five or six relatively small secondary 

 utricles, as opposed to only four or two which are the more usual 

 numbers for most species with a three-layered cortex. Occasionally the 

 intermediate zone may be absent, but this rarely happens uniformly 

 throughout the segment. 



In more basal segments of taenicola an additional layer of utricles 

 is frequently present, the length of the peripheral and secondary utricles 

 is often greater, and the breadth of the innermost utricles is towards 

 the lower limit of the range. These modifications, however, occur 

 fairly commonly throughout the genus. 



Microscopically, taenicola differs from discoidea in the somewhat 

 smaller surface diameters of the peripheral utricles, these averaging 

 57 fxm in taenicola and 65 ixm in discoidea. Other differences include the 

 relatively fewer lateral fusions of these utricles, and the degree of their 

 lateral attachment, which in taenicola is approximately half that 

 occurring in discoidea. Although the basic nodal structure is similar in 

 these two species, incomplete fusion is considerably commoner in 

 discoidea with the fusion groups at most adhering only slightly. In 

 taenicola groups of fused filaments adhere for an appreciable distance. 



The external appearance of this species sometimes leads to confusion 

 with macroloha. These two species can be distinguished macroscopically 

 on the basis of the bulbous holdfast and the somewhat fused condition 

 of the basal or suprabasal segments in macroloba. These features are 

 absent in taenicola. Histologically also, the two species are entirely 

 distinct. The peripheral utricles in macroloha often separate after 

 decalcification, and the pattern of its nodal filaments is that of the 

 section Rhipsalis. 



Halimeda bikinensis Taylor 

 Figure 43. 



Halimeda bikinensis Taylor (1950), p. 87, Plate 48, Fig. 1; Hillis (1959), 

 p. 358, Plates 2, 5, 6, 10. 



