Also known as Feather Hydroid, Fire Hydroid, Fireweed, Philippine Hydroid, Sea Fern, Stinging Bush Hydroid, Stinging Hydroid, White Stinger.
Found in colonies over shallow water coral and rocky reefs.
They feed on plankton.
Length - 3cm
Depth - 1-25m
Widespread Indo Pacific
Hydroids look like tiny ferns or feathers, many are smaller than 5cm although some can grow to 50cm.
They are found competing for space with sponges on bare patches of dead coral and rocks.
Stinging hydroid polyps are very small and are carried on the stem and side branches of feather/fern like colonies. The specific layout of the polyps on the branches, as well as the arrangement of the branches are used to classify different species.
The class Hydrozoa encompasses the most diverse group of venomous species and includes the stinging hydroids, hydrocorals (firecorals) and the portugese man of war (siphonophore)
Some species can inflict painful stings. Ref: http://www.marinelifephotography.com/marine/cnidaria/halopteris-diaphana.htm