. A manual of zoology. Zoology. III. ANTHOZOA: HEXACORALLA 231 more tentacles and only eight septa (fig. 202), but which exhibits a condition through which the young actinians pas,s; on the other hand, in the Zoantharia, Ceriantliia;, and Antipatharia the rule of six has undergone extensive modifi- cation. Sub Order I. ACTINARIA (Malacoderma). The sea-anemones are mostly solitary, witliout sl^elelon; with numerous septa and tentacles. 1 hey occur in. Fig. 203.—Astrangia dance*; five polyps in various stages of expansion. Fig. 204.—Cainria arabica (after Klunzinger). all seas from tide marks to
. A manual of zoology. Zoology. III. ANTHOZOA: HEXACORALLA 231 more tentacles and only eight septa (fig. 202), but which exhibits a condition through which the young actinians pas,s; on the other hand, in the Zoantharia, Ceriantliia;, and Antipatharia the rule of six has undergone extensive modifi- cation. Sub Order I. ACTINARIA (Malacoderma). The sea-anemones are mostly solitary, witliout sl^elelon; with numerous septa and tentacles. 1 hey occur in. Fig. 203.—Astrangia dance*; five polyps in various stages of expansion. Fig. 204.—Cainria arabica (after Klunzinger). all seas from tide marks to the greatest depth. A few are free, but most are sessile. Metridium* Bunodes* Sagartia* Bicidium* (parasitic on Cyoiiea), Halcampa*. Zoanthe^e have two kinds of alternating mesenteries, individuals of the colonies usually incrusted with foreign matter. EpiztaHthus''' lives symbi- otically with hermit crabs (fig. 114). Sub Order II. ANTIPATHARIA. Six pairs of septa and six (Antipathcs) or twenty- four (Gerardia) simple tentacles; colony with a black horny axis and no calcareous skele- ton. Simulate the Gorgonids. Sub Order III. MADREPORARIA (Scleroderma). This group, the richest in species of any, is characterized by the great development of the skeleton. Theca, septa, and usually columella are present, and fre- quently costae as well. Solitary forms are few. Usually they form colonies, frer^uently of thousands of individuals, bound together by a ccenosarc extending over the surface of the coral. A colony arises from a single animal by continued fission or budding. When the division is not complete the ani- mals may form long series with numerous mouths but with the other parts united, the result being that the surface of the coral is marked by long mnding grooves—incompletely separated theca—with sclero- septa, as in the brain corals (fig. 204). The fossil Tetracoralla (p. 230) are now regarded as modified Hexacorallans. (i) The Aporosa, a compact skel- eton, the gastr
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