This set of photomicrographs by Dr. Anita Brinckmann Voss shows a colony growing on a frond of Aglaophenia sp.

Nudibranch grazing on polyps

A densly -packed colony

see this link for other hydroids:  https://www.racerocks.ca/tag/hydroid/

Species recognized by World Register of Marine Species (WoRMS):
Biota
Animalia
Cnidaria
Hydrozoa
Hydroidolina
Anthoathecata
Filifera
Hydractiniidae L. Aggasiz, 1862
Hydractinia Van Beneden, 1841
Hydractinia laevispina Fraser, 1922

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