The American comb jelly Mnemiopsis leidyi occurred for the first time at the Swedish West Coast, 2006. Thereafter huge numbers of Mnemiopsis invaded the water around Bohuslän, Sweden. In September 2009 Mnemiopsis appeared in the Gullmar Fjord with up to 500 individuals per liter water, juveniles included. M. leidyi reduced the copepod population in the Gullmar Fjord drastically with more than 90 %. Inside the bells of some M. leidyi a planula was attached nearby the host stomodeum. The planula is a parasite and feed directly from the contents of the stomodeum of M. leidyi. Supposedly the planula belongs to an Edwardsiid anemone from Skagerrak, presumably Edwardsiella carnea (Gosse, 1856.
M. leidyi was not found in the waters around the Swedish West Coast during the years 2011 and 2012. Since the parasitic planula could not be collected these years, its morphology and cnidom is thus not record in this article. When M. leidyi, infected with the parasitic planula, again invades our waters, hopefully, we might be able to correlate the cnidom of the planula with the cnidom of its adult anemone, the presumed Edwardsiella carnea (Gosse, 1856) from Skagerrak.
The aim of this study is to describe the morphology and cnidom of the adult Edwardsiid anemone, the presumed Ella. carnea collected from Skagerrak, and to determine its taxonomy down to species level. Its morphology and cnidom correspond to the descriptions of Milne-Edwardsia carnea (Goose, 1856) Carlgren, 1892 (Carlgren 1921) and of Favesia (Milne-Edwardsia) carnea (Goose, 1856) (Carlgren, 1940). The anemone has eight mesenterial compartments (macrocoels) and belongs the family Edwardsiidae Andres, 1881, and to the genus Edwardsiella Andres, 1883 due to lack nemathybomes (nematocyst-filled pockets along the mesenteries). Ella. carnea appeared in 2 color morphs, one reddish and one lighter colored, partly translucent. Disturbed Ella. carnea will quickly and completely retract into its surrounding tube. The elongate column is differentiated into: oral disc with tentacle crown, mouth and hypostome; capitulum, the introvert, basally with a ring of yellow blotches, one blotch on each mesenterial compartment; scapus, partly hidden in the tube; and physa, the broader rounded aboral region completely inside the tube. The tentacle crown has 17 or 18 delicate, filiform tentacles arranged in 2-3 cycles. Tentacles of the inner cycle are slightly longer than those of the outer cycle. The cnidom includes broad microbasic b-mastigophores; narrow microbasic b-mastigophores; microbasic p-mastigophores; thin, long basitrichs; and spirocysts. Medium b-mastigophores are the dominating nematocysts.
The nematocyst descriptions together with the morphology made by Carlgren (1921, 1940) of Milne-Edwardsia carnea (Gosse) and of Favesia (Milne-Edwardsia) carnea (Gosse 1856) have convinced us that our Edwardsiid from Skagerrak is Edwardsiella carnea (Gosse, 1856). We are now eager to study the cnidom of the parasitic planula in Mnemiopsis leidyi, when it again appears on the Swedish west coast to see if the planula belongs to Ella. carnea.