61 — Mussel's beard, Amphisbetia bispinosa

Mussel's beard Amphisbetia bispinosa and
gammaridean amphipods, Lion Rock, Piha.

Mussel's beard (Amphisbetia bispinosa (Gray, 1843)) is not a beard, or indeed made by mussels. It is actually a colony of thecate hydroids. Theca means cup, so each individual hydroid lives inside a cup-like structure.

Hydroids are related to jellies and sea anemones. Mussel's beard is (not surprisingly) found mostly on mussels—particularly the green-lipped mussel*. However, colonies are also common on wharf piles. They are found throughout New Zealand and southern Australia.

Mussel's beard Amphisbetia bispinosa and
gammaridean amphipods, Lion Rock, Piha.

The pictures here come from Lion Rock, Piha, 24/10/16. The animals amongst the mussel's beard are gammaridean amphipods, which are abundant in the intertidal rock pools there. The amphipods are about 5–7mm in size.

Mussel's beard Amphisbetia bispinosa and
gammaridean amphipods, Lion Rock, Piha.

*Perna canaliculus (Gmelin, 1791).