220 



L. HILLIS-COLINVAUX 



with U . petiolata to be identical with the vegetative thallus of U. minima 

 Ernst. 



The development of the zygote has not been observed for Penicillus 

 but there are two reports of fertile plants with some variation in details. 

 Hillis-Colinvaux (1973) observed the conspicuous white thalli of two 

 individual Caribbean P. capitatus plants after gamete discharge in 

 aquaria. The capituli of both thalli were surrounded by a halo of brown 

 fuzz which microscopically appeared as soft, easily broken, non- 

 calcareous extensions of the capitulum filaments (Fig. 74). They were 



Fig. 74. Sexual reproduction in Penicillus. (Top) Mature Penicillus capitattis with hmsh. 

 (capitulum) covered with brownish, soft, uncalcified fuzz composed of extensions 

 of the filaments of the capitulum. Scale bar is 1 cm. (Bottom) Filaments from the 

 capitulum showing calcified (left) and uncalcified (right) portions. The uncalcified 

 portion is the presumed gametangium, although release of gametes was not observed. 

 Scale bar is 500 [xm. 



about the same diameter as the regular filaments, without obvious 

 cross walls between calcified and uncalcified portions, and were some- 

 times dichotomously branched. The tube extensions and main filaments 

 of the capitulum were essentially empty of contents, indicating dis- 

 charge, and the apical ends of the soft filaments were open (Fig. 74). 

 Meinesz (1975) observed discharge from thalli of P. capitatus f. medi- 

 terranea, and briefly described the gametangia, without figures, as 

 spherical, and up to about 30 [jim in diameter. The gametangia were 

 located among the filaments of the capitulum and discharge was by 

 rupture of their walls. 



