Fam. 1. Briareidae.—The medullary substance consists of closely packed but separate spicules embedded in a soft horny matrix, which is uniform in character throughout its course. Nearly all the genera form dendritic colonies of considerable size.
The principal genera are:—Solenocaulon, Gray; Indian Ocean and North Australia. Many of the specimens of this genus have fistulose stems and branches. The tubular character of the stem and branches is probably caused by the activity of a Crustacean, Alpheus, and may be regarded as of the nature of a gall-formation.[[376]] Paragorgia, M. Edwards; Norwegian fjords, in deep water. This genus forms very large tree-like colonies of a ruby-red or white colour. It is perhaps the largest of the dendritic Alcyonarians. It is dimorphic. Spongioderma, Kölliker; Cape of Good Hope. The surface of this form is always covered by an encrusting sponge. Iciligorgia, Ridley; Torres Straits. The stem and branches are compressed and irregular in section.
Fam. 2. Sclerogorgiidae.—The medullary mass forms a distinct axis consisting of closely packed elongate spicules with dense horny sheaths.
Suberogorgia, Gray, has a wide distribution in the Pacific Ocean, Indian Ocean, and the West Indies. Keroeides, W. and S., comes from Japan.
Fam. 3. Melitodidae.—The axis in this family exhibits a series of nodes and internodes (Fig. 155), the former consisting of pads formed of a horny substance with embedded spicules, the latter of a calcareous substance with only traces of a horny matrix. The internodes are quite rigid, the nodes however give a certain degree of flexibility to the colony as a whole. Neither the nodes nor the internodes are penetrated by nutritive canals, but when dried the nodes are porous.
Fig. 155.—Melitodes dichotoma, showing the swollen nodes and the internodes.
The principal genera are:—Melitodes, Verrill; widely distributed in the Indian and Pacific Oceans, Cape of Good Hope, etc. This genus is in some localities extremely abundant and exhibits great brilliancy and variety of colour. The branching is usually dichotomous at the nodes. Wrightella, Gray. This is a delicate dwarf form from Mauritius and the coast of South Africa. Parisis, Verrill; Pacific Ocean from Formosa to Australia but not very common. One species from Mauritius. The branches arise from the internodes.
Fam. 4. Coralliidae.—The axis is formed by the fusion of spicules into a dense, solid, inflexible, calcareous core.
Corallium, Lamarck. Corallium nobile, Pallas, the "precious coral," occurs in the Mediterranean, chiefly off the coast of North Africa, but also on the coasts of Italy, Corsica, Sardinia, and it extends to the Cape Verde Islands in the Atlantic Ocean. C. japonicum, Kishinouye, called Akasango by the fishermen, occurs off the coast of Japan, and C. reginae, Hickson, has recently been described from deep water off the coast of Timor.[[377]] The genus Pleurocorallium, Gray, is regarded by some authors as distinct, but the characters that are supposed to distinguish it, namely, the presence of peculiar "opera-glass-shaped spicules," and the occurrence of the verrucae on one side of the branches only, are not very satisfactory. The following species are therefore placed by Kishinouye[[378]] in the genus Corallium:—C. elatius, Ridley (Momoirosango); C. konojoi, Kishinouye (Shirosango); C. boshuensis, K.; C. sulcatum, K.; C. inutile, K.; and C. pusillum, K.,—all from the coast of Japan. Of the coral obtained from these species, the best kinds of Momoirosango vary in price from £30 per pound downwards according to the quality. The Shirosango is the least valuable of the kinds that are brought into the market, and is rarely exported.[[379]] Three species of Corallium (Pleurocorallium) have been described from Madeira,[[380]] and one of these, C. johnsoni, has recently been found in 388 fathoms off the coast of Ireland.[[381]] Other species are C. stylasteroides, from Mauritius; C. confusum, Moroff,[[382]] from Sagami Bay in Japan; and an undescribed species obtained by the "Siboga," off Djilolo. These corals range from shallow water to depths of 300-500 fathoms. Pleurocoralloides, Moroff, differs from the others in having very prominent verrucae and in the character of the large spindle-shaped and scale-like spicules. It was found in Sagami Bay, Japan. Specimens attributed to the genus Pleurocorallium have been found fossil in the white chalk of France, but Corallium has been found only in the tertiaries.[[383]]