It is difficult to give in a few words the characters of the order, but the Stauromedusae differ from other Scyphozoa in the absence or profound modification in structure and function of the statorhabs. They are absent in Lucernaria and the Depastridae, and very variable in number in Haliclystus.
The statorhab of Haliclystus terminates in a spherical knob, which is succeeded by a large annular pad or collar bearing a number of glandular cells which secrete a sticky fluid. At the base of the organ there is a rudimentary ocellus. The number is very variable, and sometimes they are abnormal in character, being "crowned with tentacles." There can be little doubt that the principal function of these organs is not sensory but adhesive, and hence they have received the names "colletocystophores" and "marginal anchors," but they are undoubtedly homologous with the statorhabs of other Scyphozoa.
The tentacles are short and numerous, and are frequently mounted in groups on the summit of digitate outgrowths from the margin of the umbrella. They are capitate, except in Tessera, the terminal swelling containing a battery of nematocysts.
Very little is known concerning the life-history and development of the Stauromedusae.
Fam. 1. Lucernariidae.—Marginal lobes digitate, bearing the capitate tentacles in groups. Haliclystus auricula is a common form on the shores of the Channel Islands, at Plymouth, and other localities on the British coast. It may be recognised by the prominent statorhabs situated in the bays between the digitate lobes of the margin of the umbrella. Each of the marginal lobes bears from 15 to 20 capitate tentacles. It is from 2 to 3 cm. in length. The genus occurs in shallow water off the coasts of Europe and North America, extending south into the Antarctic region.
Lucernaria differs from Haliclystus in the absence of statorhabs. It has the same habit as Haliclystus, and is often found associated with it. L. campanulata is British.
Halicyathus is similar in external features to Haliclystus, but differs from it in certain important characters of the coelenteric cavities. It is found off the coasts of Norway, Greenland, and the Atlantic side of North America.
In Capria, from the Mediterranean, the tentacles are replaced by a denticulated membrane bearing nematocysts.
The rare genus Tessera, from the Antarctic Ocean, differs from all the other Stauromedusae in having no stalk and in having only a few relatively long non-capitate tentacles. If Tessera is really an adult form it should be placed in a separate family, but, notwithstanding the presence of gonads, it may prove to be but a free-swimming stage in the history of a normally stalked genus.
Fam. 2. Depastridae.—The margin of the umbrella is provided with eight shallow lobes bearing one or more rows of tentacles. Statorhabs absent.