The structure, bionomics, and systematic position of two new brackish-water actiniaria from Madras

Abstract

1 A detailed study has been made of the morphology and systematic position of two brackish-water Actiniaria from Madras. 2 The anemones are sphincterless Athenaria having acontia, and belong to the family Halcampactiid. 3 In structural features the two anemones differ from other known Halcampactids, and this necessitates the creation of two new genera, for which the names Phytocosteopsis and Stephensonactis are proposed. 4 Complete generic and specific definitions of Phytocosteopsis ramunnii and Stephensonactis ornata are given. 5 The oral disc is very much contracted in both the Actinians, the throat being open and the distal part of the actinopharynx always remaining in an everted condition. 6 There are twelve prominent, lobed, throat ridges in S. ornata, while such separate ridges are absent in P. ramunnii.7 The tentacular arrangement in P. ramunnii exhibits a curious atypical condition, caused by the interchange of the apparent positions of the tentacles of the last two cycles and an undue development of those of the fourth order and their corresponding endoccels. 8 The acontia, which are numerous in P. ramunnii, show interesting features of distribution, correlated with the probable order of succession of the macrocnemes. They also show variations in their positions of origin from the mesentery. 9 The peculiarities of the tentacles and acontia in P. ramunnii are features not previously observed in any Actiniaria. 10 S. ornata has the tentacles and acontia arranged in the normal way, as in the typical Actiniaria. 11 The general features of anatomy and histology of S. ornata and P. ramunnii are similar. 12 An account of the bionomics of the two anemones is given, and an attempt is made to explain some of the morphological and histological peculiarities, in correlation with their habits. 13 The colour-patterns of S. ornata are described. 14 Phytocosteopsis and Stephensonactis bridge the gap between Phytoccetes and Pelocostes. Since these four genera exhibit several common characters different from other Halcampactids, a suggestion is made to group them separately in one family.