- Norwegian: Thecate hydroider
Characteristics:
The polyps always live in colonies. Each polyp live in a protective holster, unlike the polyps of the Athecate hydroids. The holster is usually long enough to enable the polyp to fully contract into it.
Taxonomy:
Thecate hydroids are one of two orders of hydroids. There are approximately 1900, all marine, species in the world today. Another, frequently used name for this order, is Leptomedusae.