Coscinasterias calamaria, or the eleven-armed sea star, is a starfish in the family Asteriidae. It was thought to be endemic to southern Australia and New Zealand but has since been documented as occurring in the Cape Peninsula as well. It is found around low tide levels and deeper, under rocks and wandering over seaweed in pools.

Description Coscinasterias calamaria is the largest starfish in southern Australia and New Zealand. Although called the eleven-armed sea star there can be any number of arms between seven and fourteen, but eleven is the most common number. These starfish are often found with arms of varying lengths. This is because arms sometimes become detached and new arms grow in their place. This starfish has rows of pincer-like pedicellariae on both its upper and lower surface which gives it a prickly appearance. Its total diameter is up to 30 centimetres (12 in).

Distribution Coscinasterias calamaria is native to the coasts of Australia and New Zealand.