Filamentous cyanophytes containing phycourobilin and in symbiosis with sponges and an ascidian of coral reefs

A study was made of the ultrastructure and pigment composition of filamentous cyanophytes living in symbiosis with several sponges and a colonial didemnid ascidian collected from the southern end of the Great Barrier Reef, Australia, between 1983 and 1986. The sponges were Dysidea herbacea and several other encrusting identified sponges; the ascidian was Trididemnum miniatum . The cyanophyte Oscillatoria spongeliae was identified as the symbiont of several sponges, including D. herbacea . 2 other unidentified Oscillatoria species were found in a bristly papillate sponge and in T. miniatum . Chlorophyll a, alone, was present in all the symbionts except T. miniatum , which contained the cosymbiont Prochloron and where chlorophyll b was also present. 2 phycoerythrins, one carrying the chromophore phycourobilin, as well as phycoerythrobilin, were isolated. Ultrastructurally, the three Oscillatoria species were distinguished by an unusual type of parallel, longitudinal, thylakoid organisation; the arrangement was different in detail in each species.