The alcyonaria may be characterized as anthozoa in which each polyp is furnished with eight tentacles, not simple, as in actinia, but furnished with pinnate margins, wills eight somatic chambers, and eight mesenteries. With the exception of one genus they are all composite in structure; their polyps being connected with one another by a ccenosarc, which is traversed by prolongations of the somatic cavity of each polyp, a system of canals being thus formed whose parts freely communicate and are readily dis tensible. Carus, in the lIandbuch der Zooloyie, 1863, vol. 2 (of which he is joint author with Peters and Gerstaecker), mainly adopting Milne-Edwards's arrangement, divides the alcyonaria into the three following families: 1, aleyonida; 2, gorgomdce; 3, pennatu ln the alcyonida he includes the beautiful organ-pipe corals, of which Green and others make a separate family. The polypidom constructed by tuldpara maim consists of successive stages of cylindrical tubes of a- rich. crimson color, mailed at various heights by means of horizontal connecting plates. The tribes placed upon the upper stage are alone inhabited by living polyps, of a violet or green color, the occupants of those below having successively perished as fresh generations appeared above them. As an example of the goryonida we may take iris hippuris, in which the skeleton is made up of alternate joints of calcareous and horny matter, with the view of giving the necessary flexibility. In the pennatulidce, the polypidom is free, and no polyps are attached to its basal portion. The sea-pens (pensatula) of our own coast afford a good example of this family. See PENNATULA for description and figure.
The zoantharia may be characterized as ant.hozoa in which the tentacles are either simple or branched, in general numerous, and together with the mesenteries, disposed in multiples of live or six. They may be arranged in the three following suborders: 1. Z. malacodermata; 2. Z. sclerobasica or ant-ipatharia (Milne-Edwards); and 3. Z. scleroder
viola or madrepores. The first sub-order has been variously subdivided into families and subfamilies, which it is unnecessary to notice. It contains all the sea-anemones and animals allied to them, including the genera -actinia, corynactis, capnea, adamsia, ilyanthus, sagartia, bunodes, eduardsia, pcachia, etc., and the zoanthidce, which are aggregated 'polyps arising from a common creeping root-like fleshy band, and of which at least one species, zoanthus couchii, is an inhabitant of the British seas. All the mem bers of the second sub-order are composite structures. Antipathe•, the type of the group, presents a stem-like, simple, or branching ceenosarc, which in one species tapers to a length of more than 9 ft., with a diameter at the base not exceeding three-tenths of an inch. '1 he third sub-order (the madrepores) is a very extensive one. it is divided into the madrepe-ra aporosa and 2/". pcsforata. according as the coral exhibits a solid or a porous structure. if. apo-rosa may be arranged in the following families: 1. turbinoticke ( neludi»g the sub-families cat yophyllivce and turbinolina); 2. °Mirada; 3. astraida; 4. echinoporince; 5. merulinacea; 6. fbngida, while the N. perforata are divided into (1)2nadre porida and (2) poritida. A few of the commoner forms of madrepora are described in the articles CORAL and MAratEronE. Among the most important works on this department of zoology may be mentioned Dana's Structure and Classification of Zoophytes (Philadelphia, 1846); and his Report on Zoophytes, and Atlas of Zoophytes (U. S. exploring expedition), 1849; Johnston's British Zoophytes, in 2 vols., to which we are indebted for many of our illustrations; Milne-Edwards and Hahne, Ilistoire Katurelle des Coralliaires ou Polypes p•oprement dits (3 vols., 1857-60): and Lacaze-Duthiers, Itistoire Naturelle du Corail, Organisation, Reproduction, etc. (1864).