Fig. 160.—Renilla reniformis, a small specimen (34 mm.), showing the dorsal side of the expanded rachis. A, autozooid; H, the mouth of the axial zooid; s, siphonozooid; St, the short stalk. (After Kölliker.)
Sect. 3. Renilleae.—This section contains a single family Renillidae and a single genus Renilla (Fig. 160). The rachis is expanded into a flattened cordate form set at an angle to the peduncle, and the zooids are confined to the dorsal surface, which is uppermost in the natural position of the colony. The peduncle is short and does not contain an axial skeleton. The colour of this Sea-pen is usually violet when dried or preserved. Specimens of Renilla are very abundant in shallow water in some localities on the Atlantic and Pacific coasts of N. America, but the genus has also been obtained from the Red Sea and the coast of Australia. A popular name for this genus is "Sea pansy."
Sect. 4. Veretilleae.—This section contains a number of genera in which the bilateral arrangement of the zooids is obscured by their gradual encroachment on the dorsal side of the axial polyp. The rachis and peduncle are thick and fleshy, and the autozooids and siphonozooids are irregularly distributed all round the rachis. The genus Cavernularia is not uncommonly found in moderate depths of water in the Indian and Pacific Ocean, and is distinguished from the other genera by the reduction of the skeletal axis. Other genera are Veretillum, Mediterranean and Atlantic Ocean, and Lituaria, Indian Ocean.
Fig. 161.—Cavernularia obesa. Au, autozooid; Si, siphonozooid; St, stalk. (After Kölliker.)
CHAPTER XIV
ANTHOZOA (CONTINUED): ZOANTHARIA
Sub-Class II. Zoantharia.
The Zoantharia exhibit a great deal more diversity of form and structure than the Alcyonaria. The sub-class is consequently difficult to define in a few words, and it may be taken to include all the Anthozoa which do not possess the typical Alcyonarian characters.