''Hydractinia altispina'', or high-spined commensal hydroid, is a small colonial hydroid in the

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

Hydractiniidae Hydractiniidae is a cnidarian family of athecate hydroids Anthoathecata, or the athecate hydroids, are an order of hydrozoans belonging to the phylum Cnidaria. A profusion of alternate scientific names exists for this long-known, heavily di ...

Description

High-spined commensal hydroids grow as a fuzzy-looking orange coat usually on the shell of a

marine snail A snail is, in loose terms, a shelled gastropod. The name is most often applied to land snails, terrestrial pulmonate gastropod molluscs. However, the common name ''snail'' is also used for most of the members of the molluscan class G ...

, the scaly dogwhelk ''

Nucella squamosa ''Nucella squamosa'', common name the scaly dogwhelk, is a species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the larg ...

''. Individual polyps grow to 0.4 cm in total height. The polyps are naked and cluster on the shell surface, interspersed with defensive spines and tiny ball-like reproductive structures.Millard, N.A.H. 1975. Monograph on the Hydroida of Southern Africa. ''Ann. S. Afr. Mus.'' 68:1-513

Distribution

This colonial animal is found only off the southern African coast from Luderitz to False Bay, Cape Town subtidally and to at least 30m under water.

References

Hydractiniidae Animals described in 1955 {{anthoathecata-stub