hydroid

The image caption has also been updated to clarify that not all hydroid animals are coastal.

The illustration shows a plant on which the hydroid Sertularia pumila is growing.

A hydroid about one inch high, growing in patches and appearing like tufts of moss on rocks between tide-marks.

There are some species which, having no hydroid or strobila state, mature without alternation of generation (metagenesis).

This hydroid is found creeping over seaweeds in tide-pools from Long Island Sound northward.

The hydroid Hydractinia polyclina often covers the exterior of such shells with a brown, velvety growth.