The gastropores and dactylopores are arranged in various ways at the surface, a common pattern being the formation of a cyclosystem (fig. 60), in which a central gastrozoid is surrounded by a ring of dactylozoids (fig. 61). In such a system the dactylopores may be confluent with the gastropore, so that the entire cyclosystem presents itself as a single aperture subdivided by radiating partitions, thus having a superficial resemblance to a madreporarian coral with its radiating septa (figs. 62 and 63). [Illustration: FIG. 62.--Diagrams illustrating the successive stages in the development of the cyclosystems of the _Stylasteridae_. (After Moseley.) 1, _Sporadopora dichotoma_. 2, 3, _Allopora nobilis_. 4, _Allopora profunda_. 5, _Allopora miniacea_. 6, _Astylus subviridis_. 7, _Distichopora coccinea_. s, Style. dp, Dactylopore. gp, Gastropore. b, In fig. 6, inner horseshoe-shaped mouth of gastropore.] The gastrozoids usually bear short capitate tentacles, four, six or twelve in number; but in _Astylus_ (fig. 63) they have no tentacles. The dactylozoids have no mouth; in _Milleporidae_ they have short capitate tentacles, but lack tentacles in _Stylasteridae_. The gonosome consists of free medusae in _Milleporidae_, which are budded from the apex of a dactylozoid in _Millepora murrayi_, but in other species from the coenosarcal canals. The medusae are produced by direct budding, without an entocodon in the bud. They are liberated in a mature condition, and probably live but a short time, merely sufficient to spread the species. The manubrium bearing the gonads is mouthless, and the umbrella is without tentacles, sense-organs, velum or radial canals. In the _Stylasteridae_ sessile gonophores are formed, always by budding from the coenosarc. In _Distichopora_ the gonophores have radial canals, but in other genera they are sporosacs with no trace of medusoid structure. [Illustration: FIG. 63.--Portion of the corallum of _Astylus subviridis_ (one of the Stylasteridae), showing cyclosystems placed at intervals on the branches, each with a central gastropore and zone of slit-like dactylopores. (After Moseley.)] _Classification._---Two families are known:-- 1. _Milleporidae._--Coenosteum massive, irregular in form; pores scattered irregularly or in cyclosystems, without styles, with transverse tabulae; free medusae. A single genus, _Millepora_ (figs. 60, 61).