The shape and the idea: 84 — Comb star, Astropecten polyacanthus

Tuesday 15 November 2016

84 — Comb star, Astropecten polyacanthus

The comb star, (Astropecten polycanthus, Müller & Troschel, 1842) is found in northern areas of New Zealand's North Island. They are also found all over the Pacific in warm seas and can grow to about 15cm across. Comb stars live in sandy sediments, from low tide down to a few metres depth, and can often be seen emerging from the sand on the turn of the tide.

The surface of the comb star (and other starfishes and seastars) are covered with small upward-facing wrench-like appendages called pedicellariae (one of my favourite scientific words btw). Pedicellariae make the upper (aboral) surface of the comb star an unpleasant place to land and settle. They do this by intercepting anything trying to settle and then encrust the surface of the comb star. This is why you don't see starfishes covered in any encrusting organism.

Comb stars have been known to contain poisonous levels of tetrodotoxin, so it's probably not a good idea to try and eat one. This also probably goes some way to explaining why you often see them upside down (in a seemingly vulnerable position), after emerging from the sand at low tide. However, despite this, it has been reported that the trumpet shell Charonia lampas (Linnaeus, 1758) predates them and can in fact sequester the toxins from the comb star.

Comb stars are thought to be predators on sand-living invertebrates (e.g., polychaete worms and molluscs), and a recent study suggests that they are important in the regulation of some gastropods and bivalves.