ECOLOGY AND TAXONOMY OF Holimeda 2Y1 



generations of Penicillus, Rhipocephalus and Udotea have generally 

 been produced in my culture systems more rapidly than those of 

 Holimeda (Table XVII). For Penicillus the plants are also considerably 

 shorter-lived, a Penicillus thallus living about two months. 



Three types of thallus have developed from the Penicillus capitatus 

 Lamarck plants in culture : 



typical thallus with stalk and brush, which is the commonest; 

 thallus of a very few filaments about 1-4 cm tall which some- 

 times branch dichotomously (Fig. 73); 



cluster of filaments similar to those of the preceding type. 



The second and third types of thallus resemble the espera condition of 

 the forma mediterranea of the genus (Huve and Huve, 1961; Meinesz, 

 1972a; Roth and Friedman, 1976). The espera phase was first described 

 as a distinct genus, Espera mediterranea Decaisne, then transferred to 

 the genus Penicillus as P. mediterraneus (Decaisne) Thuret. Huve and 

 Huve (1961) demonstrated that it was a stage in the life-cycle of 

 Penicillus capitatus f. mediterranea (Decaisne) Huve and Huve. Vigorous 

 Penicillus thalli can also regenerate a new capitulum if the old one is 

 removed (Kupfer, 1907; Hillis-Colinvaux, 1973). 



Sexual stages appear to be infrequent, again partly because the 

 thallus is destroyed in the process. They are known for Udotea (Niza- 

 muddin, 1963; Meinesz, 1969, 1972c) and Penicillus (Colinvaux, 1969b; 

 Hillis-Colinvaux, 1973; Meinesz, 1975). In Udotea the edge of the thallus 

 becomes fringed with loose filaments (Nizamuddin, 1963 ; Meinesz, 1969) 

 which appear to be short extensions of the filaments of the blade of the 

 fan. Biflagellated gametes are released from the tips of the filaments 

 (or gametangia) early in the morning, and thalli connected by stolons 

 release their gametes at the same time (Meinesz, 1969). 



The gametes are anisogamous and are borne on separate thalli for 

 U. petiolata (Turra) Borgesen, with only the macrogametes possessing 

 an eyespot (Meinesz, 1969) as in Halimeda. 



The development of the zygote of Udotea petiolata has been followed 

 (Meinesz, 1972c), using the same techniques as for Halimeda. An irregu- 

 larly shaped, somewhat flattened protosphere was first produced which 

 reached its maximum development in culture in five months, with a 

 diameter of between 60 fxm and 90 yun, a single nucleus of 6-9 fxm 

 diameter, 200-300 chloroplasts and no amyloplasts. The protosphere 

 subsequently produced two filamentous outgrowths from which a mass 

 of filaments developed, which were heteroplastic and coenocytic, and 

 were of the same general form as the filaments produced by the Hali- 

 meda zygote. Meinesz considered the filamentous stage he obtained 



