Stauromedusae are little jellyfishes that spend their entire life attached to the substrate (rock or algae, usually), rather than swimming freely up in the water column like most other jellyfish. They have long been considered an an Order (Stauromedusae) in the Class Scyphozoa of the Phylum Cnidaria, but recent morphological and molecular studies (Marques and Collins, 2004; Collins and Daly, 2005) argue convincingly that they should be elevated to a rank equal to both the Scyphozoa and Cubozoa, as the Staurozoa. For those who insist on applying taxonomic ranks, these might now all be considered Classes, but many scientists are pulling away from the concept of tight adherence to the old hierarchies of rank, in which case just "Staurozoa" will do.
I have compiled a list of all valid scientific names for Stauromedusae. There are about 50 known species worldwide and most are less than 5 cm long. They typically live in cold water. Few scientists have studied stauromedusae, so not so much is known about them, although they are not uncommon along many undisturbed rocky shorelines in Europe and northern North America and Asia. Some have also been found in temperate regions in the southern hemisphere. Most stauromedusae are colored to blend in well with their surroundings and are seen only by the most careful observers. Most are found in the low intertidal to shallow subtidal shoreline area.
The photograph on the left is Manania handi, a little-known stauromedusa that lives attached to eelgrass on the shores of some islands in northwestern Washington State and southwestern British Columbia. It is colored very much like the eelgrass from which it is hanging (see adjacent photo for eelgrass color), making it difficult to see in the field.
The photograph on the right is Haliclystus "sanjuanensis", which lives in the same eelgrass bed as Manania handi, above. This is one representative of a species complex whose members are found in both the north Atlantic and Pacific oceans in temporal and boreal waters. I have recently been studying the natural history of both of the above species.
Since stauromedusae do not swim, they have rather limited dispersal potential. They can move around, though, often gradually moving their base along the substrate (like some sea anemones); some species release at the base and use their adhesive tentacles to "somersault" along. Rarely, stauromedusae have even been seen drifting free in the water, after having released at the base. The larvae of stauromedusae are simple elongate planulae that lack the cilia of other cnidarian classes. These tiny larvae move by creeping along, thus having much less dispersive ability than the typical planktonic planulae that swim using their cilia.
There are a few other nice photographs of stauromedusae available on the Web. Click here and here to see two nice photographs of stauromedusae representing quite different morphologies than the two photographs on this page.
One of the most interesting new observations of stauromedusae was made by Richard Lutz and colleagues, who visit deep-sea hydrothermal vents by submersible and have discovered that a new species of stauromedusa is the dominant organism in at least two particular areas (see Deep-Sea Research Part II, volume 45, pages 329-334, 1998). At the first location, a 2605 m deep vent along the East Pacific Rise, many stauromedusae (of a single species) were located within a fissure of an active vent site. The numerous stauromedusae (Lucernaria janetae Collins and Daly, 2005) at the 2750 m "Sarah's Spring" vent site, also on the East Pacific Rise, are pictured here. It is very exciting to find this typically shallow, shoreline kind of organism as a main player in such a different ecosystem.
