Changes

*The symbiotic association of the sponge ''Sigmadocia symbiotica'' Bergquist & Tizard and the alga ''C. spongiosum'' forms clumps of 15-30(-70) cm in diameter and 5-15 cm tall. These associations are green-brown to purple, distinctly sponge-like, subcylindrical or compressed, hard and tough. *Branching very irregular and often anastomosing, 5-10(-20)mm in diameter and with many ostioles of the sponge. Intertwining and anastomosing algal axes form a dense reticulum within the sponge cover. Specimens anchored at numerous points to solid substrates by slightly splayed but otherwise unmodified bases or lateral extensions of major axes (no expanded discs or thickened holdfasts). *Algal axes terete, 100-300(-400) μm in diameter, with a single-layered outer cortex, a pseudoparenchymatous inner cortex and a medulla of a compact core of narrow filamentous cells; distinct apical cell absent, growth by small cells in dome-shaped, multiaxial apex. *Life cycle triphasic, diplo-haplontic and isomorphic. *Tetrasporangial sori in apical, aggregated, swollen, cylindrical stichidia, about 1.5 mm long, on modified terminal algal branches projecting into sori from the tips of the branches of the symbiotic association; tetrasporangia irregularly decussate, about 10-15 μm × 20-25 μm, surrounded by tissue of narrow (3 μm) anticlinal rows of cortex cells. *Gametophytes dioecious; male ones forming swollen, exerted axes superficially resembling tetrasporangial stichidia, although more mucilaginous and covered by spermatangial mother cells, each forming 1-2 distal spermatangia; female ones with dense clusters of terete to slightly flattened protruding terminal branches, simple or sparingly branched, covered by aggregates of cystocarps with often partly confluent pericarps. *Mature cystocarps protuberant, about 600 μm in diameter, bluntly conical, with apical ostiole.

The algal ( ''C. spongiosum'' ) and sponge partners reproduce completely independently of one another. It is not known when, or how, the symbiosis is established. Sponge-free algal growth has been established in laboratory culture, but the sponge partner has never been found free-living, and attempts to maintain it separately in laboratory culture have failed.

Other ''Ceratodictyon'' spp. recorded from the area, except C. ''spongiosum'' , are possibly subspecies of ''C. intricatum'' (C. Agardh) R.E. Norris. The placement of ''Ceratodictyon'' Zanardini in the family ''Rhodymeniaceae'' of the order Rhodymeniales replaces earlier inclusion in the family ''Gracilariaceae'' of the order Gigartinales. The relationship between ''Ceratodictyon'' and ''Gelidiopsis'' F. Schmitz and their taxonomic placement is not yet solved.

There is no known phycoculture of ''C. spongiosum'' .

''C. spongiosum'' may become a source of fine chemicals and pharmaceuticals, especially because sponges are known to contain many interesting biopharmaceutical compounds. Most sponges are difficult to find regularly and in suitable quantities, but because of the symbiotic association with ''C. spongiosum'' , ''Sigmadocia symbiotica'' can be easily identified and collected.

*G.C. Trono Jr