- Colony of Hydractinia echinata, growthemselves; or, ing on the Shell of a Whelk.
- Polyps from a Colony indicated in the case of the polyps of Hydractinia, magnified.
5, A) and Hydractinia (figs.
The evidence against this view may be classed under two heads: first, comparative evidence; hydroids very different in their structural characters and widely separate in the systematic classification of these organisms may produce medusae very similar, at least so far as the essential features of medusan organization are concerned; on the other hydroids closely allied, perhaps almost indistinguishable, may produce gonophores in the one case, medusae in the other; for example, Hydractinia (gonophores) and Podocoryne (medusae), Tubularia (gonophores) and Ectopleura (medusae), Coryne (gonophores) and Syncoryne (medusae),-and so on.
(From Moseley.) hydroid such as Hydractinia to the hydrocoralline Millepora is not great.
Ceratella stands in much the same relation to the Stylasteridae that Hydractinia does to the Milleporidae, in both cases the chitinous perisarc being replaced by the solid coenosteum to which the hydrocorallines owe the second half of their name.