ECOLOGY AND TAXONOMY OF Holimeda 



239 



Tydemania, as a putative primitive Codiacean, may have survived in 

 abundance only in deep-water habitats. Although it grows well in this 

 environment, it also occurs in sizeable populations at some sites of 

 3-5 m depth in Enewetak Lagoon, the same lagoon in which Gilmartin 

 worked (Hillis-Colinvaux, 1977), and I have observed well-developed 

 stands of it in water of — 1 m to —4m in the Indian Ocean near the 

 small islands of Banyak, Batu, Siburu and Stupai off the west coast of 

 Sumatra. 



The distributional data for the genera of the Caulerpales (Table XX) 

 provide the basis for a new scheme (Fig. 78). It is suggested that the 



Indo- Pacific 



Atlantic 



Tydemania 

 Callipsygma 



Chlorodesmis 

 ( incl. Rhipldodesmis at least pp.) 



Geppella 

 Rhipiliopsis 



Penicillus 

 Rhipocepha I us 



/ 



/ 



/ 



/ 



/ 



/ 



L^^Z. 



Halimeda - Udotea 



Avrainvl Ilea 



Pseudocodium 



Pantropical 



Fig. 78. New phylogenetic scheme of Caulerpales, excluding the monogeneric Cauler- 

 paceae, based on biogeographic data. 



five pantropical genera Halimeda, Udotea, Avrainvillea, Caulerpa and 

 Pseudocodium are the oldest, and had differentiated before free east- 

 west exchange of tropical marine biota was brought to an end by the 

 closing of the Tethys Sea. The other genera may have coexisted with 

 them and subsequently have become extinct over part of the range, or 

 they may have evolved later. Considering the present distribution of 

 these genera, at least as known, the latter seems the more likely inter- 

 pretation for the taxa of all but the last column which are not included 

 in the scheme because the distributional patterns shown for them are 

 interpreted as reflecting incomplete data. One or more of the genera in 



