89 — Eleven-armed starfish, Coscinasterias muricata

Coscinasterias muricata, Piha, 9/2/15.

Coscinasterias muricata, Piha, 9/2/15.

Coscinasterias muricata, Piha, 9/2/15,
macro shot showing the pedicellariae.

Coscinasterias muricata Verrill, 1870, is a large sea star (~20cm across). They are found throughout New Zealand and southern Australia where they are inter-tidal to sub-tidal. Although they are known as eleven-armed sea stars, this number can vary. For example, the one pictured her only has ten arms.

They are especially common under mussel farms, where they prey on fallen mussels. Elsewhere, they are reported to feed on gastropods and bivalves, particularly (again mussels and) oysters.

In the third picture below you can see the small upward-facing wrench-like appendages called pedicellariae, in a ring around white-coloured spines. These guard against ant attempts by encrusting organisms to settle. Encrusting organisms could reduce the flexibility and mobility of the starfish and therefore reduce its chances of survival.















More info:

Morton, J. E., Miller, M. C. 1968. The New Zealand Sea Shore. Collins.

NIWA sea star identification guide:
https://www.niwa.co.nz/static/extraordinary_echinoderms.pdf