Siebert, Arthur E Jr.2008-03-142008-03-141973-10Siebert AE Jr. 1973. A description of the sea anemone Stomphia didemon sp. nov. and its development. Pac Sci 27(4): 363-376.0030-8870http://hdl.handle.net/10125/815Stomphia didemon is described as a new species of sea anemone from the San Juan Archipelago, Washington. It possesses about 192 tentacles and 96 pairs of mesenteries. The cnidom is spirocysts, basitrichs, microbasic b-mastigophores, and microbasic p-mastigophores. S. didemon spawned in April and May. The eggs are 750 to 800 /lm in diameter, orange, and centrolecithal; cleavage is superficial, equal, and incomplete. Endoderm formation is by unipolar ingression from a fold in the surface of the blastula. Settlement of the planulae is favored by the presence of sand or gravel. Attempts were made to fertilize eggs of S. coccinea with sperm from S. didemon, but the cross-fertilized eggs failed to develop.en-USArticle