Liriantha appendiculata sometimes occurs on the south coast of England during September, October, or at other times.
Order VIII. Narcomedusae.
The Narcomedusae differ from the Trachomedusae in having the margin of the umbrella divided into a number of lobes, and in bearing the gonads on the sub-umbrellar wall of the gastral cavity instead of upon the radial canals. The tentacles are situated at some little distance from the margin of the umbrella at points on the aboral surface corresponding with the angles between the umbrella lobes. Between the base of the tentacle and the marginal angle there is a tract of modified epithelium called the "peronium." The manubrium is usually short, and the mouth leads into an expanded gastral chamber which is provided with lobular diverticula reaching as far as the bases of the tentacles. The marginal sense-organs are in the form of unprotected statorhabs. Very little is known concerning the life-history of any of the Narcomedusae. In Cunoctantha octonaria the peculiar ciliated larva with two tentacles and a very long proboscis soon develops two more tentacles and creeps into the bell of the Anthomedusan Turritopsis, where, attached by its tentacles, it lives a parasitic life. Before being converted into a Medusa it gives rise by gemmation to a number of similar individuals, all of which become, in time, Medusae. The parasitic stage is often regarded as the representative of the hydrosome stage reduced and adapted to the oceanic habit of the adult.
In Cunina proboscidea, and in some other species, a very remarkable method of reproduction has been described by Metschnikoff, called by him "sporogony." In these cases young sexual cells (male or female) wander from the gonad of the parent into the mesogloea of the umbrella, where they develop parthenogenetically into ciliated morulae. These escape by the radial canals into the gastric cavity, and there form a stolon from which young Medusae are formed by gemmation. In C. proboscidea these young Medusae are like the genus Solmaris, but in C. rhododactyla they have the form of the parent. In some cases the ciliated larvae leave the parent altogether and become attached to a Geryonia or some other Medusa, where they form the stolon.
This very interesting method of reproduction cannot be regarded as a primitive one, and throws no light on the origin of the order. It might be regarded as a further stage in the degeneration of the hydrosome stage in its adaptation to a parasitic existence.
The Narcomedusae have a wide geographical distribution. Species of Aeginopsis occur in the White Sea and Bering Strait, but the genera are more characteristic of warmer waters. Some species occur in moderately deep water, and Cunarcha was found in 1675 fathoms off the Canaries, but they are more usually found at or near the surface of the sea.
Fam. Cunanthidae.—Narcomedusae with large gastral diverticula corresponding in position with the bases of the tentacles. Cunina and Cunoctantha, occurring in the Mediterranean and in the Atlantic and Pacific Oceans, belong to this family. In Cunina the tentacles may be eight in number, or some multiple of four between eight and twenty-four. In Cunoctantha the number of tentacles appears to be constantly eight.
Fam. Peganthidae.—There appear to be no gastral pouches in this family. The species of Pegantha are found at depths of about 80 fathoms in the Indian and Pacific Oceans.
Fam. Aeginidae.—The large gastral pouches of this family alternate with the bases of the tentacles. Aegina occurs in the Atlantic and Pacific Oceans. Aeginopsis.
Fam. Solmaridae.—In this family the gastral pouches are variable, sometimes corresponding with, sometimes alternating with, the bases of the tentacles. The circular canal is represented in some genera by solid cords of endoderm. Solmaris sometimes appears in the English Channel, but it is probably a wanderer from the warmer regions of the Atlantic Ocean. It is found in abundance during November on the west coast of Ireland.