733 THE ANIMAL KINGDOM. 



The classification of the Alcyonaria is by no means settled in details. The 

 following groups however may be distinguished. 



I. Non-colonial forms = Proto-Alcyonaria (Hickson). 



Haimeidae. Three genera only ; Monoxenia, from Arabian coast ; Haimea, 

 from Fiji Islands ; Hartea, from west coast of Ireland. 



II. Colonial forms. 



1. Cornularidae. Zooids originating from a tubular stolon, e.g. Clavularia, a 

 band-like stolon, Sarcodidyon, or a basal expansion, Sympodium. They are usually 

 free ; but Clavularia viridis has connecting tubes between the zooids from which 

 new zooids may spring. 



2. Tubiporidae. Zooids originating from a basal disc and connected by 

 platforms from which new zooids spring spicules uniting to form a continuous 

 system of tubes and platforms ; Tubipora. 



Hickson unites i and 2 into a group, Stolonifera. 



3. Alcyonidae. Zooids forming a more or less massive colony ; rarely dimor- 

 phic as in Sarcophyton and Heteroxenia ; no skeletal structures save scattered 

 calcareous spicules ; gastric cavities of zooids remarkably long ; Alcyonium^ &c. 



Coelogorgia, from Zanzibar, which forms branching colonies with tubular axes, 

 and one or two allied forms perhaps belong here. 



4. Pseudaxonia. An axial branched skeleton present, derived entirely from 

 cells of the mesoglaca. This axis consists of fused calcareous spicules in the 

 Corallinae, e. g. Corallium rubrum ; of calcareous spicules cemented by horny 

 lamellae in the Sclerogorgiacea ; of alternating joints, one set composed of spicules 

 united by horny lamellae, the other of fused spicules, Melitheacea^ i. e. Melithea and 

 Mopsea. 



Siphonogorgia and Paragorgia with a spicular axis form a transition to 3. 

 They have dimorphic zooids ; so too probably Corallium. 



5. Axifera. An axial branched skeleton present, derived from a layer of ecto- 

 derm cells invaginated from the base of the colony ; skeleton lamellate, horny, or 

 horny and calcareous; in Isis composed of alternating horny and calcareous 

 joints ; Primnoa, Gorgonia, &c. 



6. Pennatulidae. Colony free, with a base or peduncle sunk in sand or mud. 

 Zooids dimorphic ; confined to the exposed part of the colony. An axial skeleton 

 generally present, covered by an epithelium, probably of endodermic origin. Some 

 are phosphorescent. Virgularia, Funiculina, Pennatula, Renilla, Umbellula, &c. 



7. Helioporidae. A calcareous skeleton composed of lamellae of calcite, as in 

 the Madreporarian Zoantharia. Zooids dimorphic. Siphonozooids reduced to 

 short closed tubes. The calcareous cups for the zooids are closed below by 

 horizontal tabulae, which are formed successively during the growth of the coral, 

 one at some little distance above another. Heliopora, from the Philippine Islands. 



General literature. Milne Edwards and Haime, Histoire Nat. des Coral- 

 liaires, 3 vols., Paris, 1857-1860. Klunzinger, Korallthiere des Rothen Meeres, 

 (with lit.) 3 pts., Berlin, 1877-1879. On the skeleton^ von Koch, Biol. Centralblatt, 

 ii. 1882-83. 



Monoxenia^ Haeckel, Arabische Korallen, 1876, p. 7; Hartea, P. Wright, 

 Q. J. M. v. 1865 \ Haimea, Milne Edwards, Histoire Nat. des Coralliaires, Paris, i. 

 1857, p. 104. 



