FRESH-WATER EPIPHYTIC CYANOPROKARYOTES FROM CENTRAL MEXICO .2. HETEROGENEITY OF THE GENUS XENOCOCCUS

Second article of the series of studies about the cyanoprokaryotic (cy anophycean, cyanobacterial) species, growing epiphytically on submerse d filamentous algae in central Mexico. The traditional genus Xenococcu s was found to be heterogeneous and the stability and frequency of int er- and intrageneric characters was studied in natural populations fro m central Mexican streaming waters, sampled in the period from 1983 to 1993. The types of cellular binary fission and nanocytic cell divisio n were particularly studied, and from them were derived different life -cycle strategies. The genus Xenotholos gen.n. was separated from the genus Xenococcus on the basis of these results, and seven species were studied from both genera (one new species of Xenococcus and three new species of Xenotholos were described). Characteristics of all species studied are included. Another group of traditional Xenococcus-species , which does not correspond morphologically either to Xenococcus or to Xenotholos, and cells of which never divide by multiple fission, must be also separated from the genus Xenococcus (X. minimus type).