|Chrysaora achlyos: Black sea nettle
Phylum Cnidaria / Class Scyphozoa / Order Semaeostomeae / Family Pelagiidae
You won’t encounter this impressive gelatinous beast very often, but if you do it will surely be a memorable experience. The photos here show the strikingly beautiful purplish oral arms and several of the 24 white to light pink tentacles. The silvery fish are Pacific butterfish (Peprilus simillimus), which frequently associate with large jellies for protection as juveniles. The black sea nettle can be quite massive, with a bell diameter potentially up to 1 meter and oral arms extending to 5 or 6 meters. The bell color is a distinctive opaque dark purple to nearly black, with the margin having a lighter brown reticulated pattern. No other West Coast jelly that visits nearshore waters has this dark pigmentation. Four gonads are attached to finger-like projections that extend through subumbrellar openings (the ostia). Marginal sense organs are spaced around the bell margin after every set of 3 tentacles, for a total of 8.
Black sea nettles are occasionally seen in large numbers in surface waters off the coast of Baja California and southern California, and large swarms have occurred in recent years. During most years their whereabouts are unknown. Despite the distinctive nature of this species and its abundance when present, it was only recently officially described, and is actually the largest invertebrate to have been described in the 20th Century. Published accounts have described the northern range of the black sea nettle extending to southern California, but a large individual was seen in Carmel Bay (near the Monterey Peninsula) in September 2001.