Fig. 136.—A portion of a branch of Cryptohelia ramosa, showing the lids l 1 and l 2 covering the cyclosystems, the swellings produced by the ampullae in the lids amp1, amp2, and the dactylozooids, dac. × 22. (After Hickson and England.)
A few specimens of a species of Stylaster have been found in Tertiary deposits and in some raised beaches of more recent origin, but the order is not represented in the older strata.
Fam. Stylasteridae.—All the genera at present known are included in this family.
Sporadopora is the only genus that presents a superficial general resemblance to Millepora. It forms massive, branching white coralla, with the pores scattered irregularly on the surface, and, like many varieties of Millepora, not arranged in cyclosystems. It may, however, be distinguished at once by the presence of a long, brush-like style in each of the gastropores. The ampullae are large, but are usually so deep-seated in the coenenchym that their presence cannot be detected from the surface. It was found off the Rio de la Plata in 600 fathoms of water by the "Challenger."
In Errina the pores are sometimes irregularly scattered, but in E. glabra they are arranged in rows on the sides of the branches, while in E. ramosa the gastropores occur at the angles of the branches only. The dactylopores are situated on nariform projections of the corallum. The ampullae are prominent. There are several gonophores in each ampulla of the male, but only one in each ampulla of the female. This genus is very widely distributed in water from 100 to 500 fathoms in depth.
Phalangopora differs from Errina in the absence of a style in the gastropore; Mauritius.—Pliobothrus has also no style in the gastropore, and is found in 100-600 fathoms of water off the American Atlantic shores.
Distichopora is an important genus, which is found in nearly all the shallow seas of the tropical and semi-tropical parts of the world, and may even flourish in rock pools between tide marks. It is nearly always brightly coloured—purple, violet, pale brown, or rose red. The colony usually forms a small flabellum, with anastomosing branches, and the pores are arranged in three rows, a middle row of gastropores and two lateral rows of dactylopores on the sides of the branches. There is a long style in each gastropore. The ampullae are numerous and prominent, situated on the anterior and posterior faces of the branches. Each ampulla contains a single gonophore in the female colony and two or three gonophores in the male colony.
Spinipora is a rare genus from off the Rio de la Plata in 600 fathoms. The branches are covered with blunt spines. These spines have a short gutter-like groove at the apex, which leads into a dactylopore. The gastropores are provided with a style and are situated between the spines.
Steganopora[[321]] from the Djilolo Passage, in about 600 fathoms, is very similar to Spinipora as regards external features, but differs from it in the absence of styles in the gastropores, and in the wide communications between the gastropores and dactylopores.