The growth is pinnate, with alternate secondary branches which are parallel to one another and join the main stem at an angle of about 50°, giving a herring-bone appearance.

These in turn have stubby tertiary branches which bear the hydrothecae (feeding polyps); these grow on alternate sides of the stem, forming short, equal-length segments, separated by transverse nodes.

In the eastern Pacific Ocean its range extends from Alaska to California and it is also present in the Mollucas, Japan and the Sea of Okhotsk.

[5] It grows on hard surfaces such as shells and stones in the shallow sub-littoral zone and in deeper water.

[7] The second type has a longer, extensible column and fewer, shorter, thicker tentacles armed with larger stinging cells.