Unlike all other starfishes in Icelandic waters, the sunstars have more than five arms (see also the purple sunstar). In fact, the number of arms differ by individuals, in the common sunstar they are usually 10 to 12.
The common sunstar can be up to 35 mm in diameter. It is red, reddish-yellow or purple in colour with a regular pattern from the central disc. The arms are relatively short compared to other starfishes.
The common sunstar is found in cold seas in the northern hemisphere, both in the North Atlantic and in the eastern North Pacific. It is found on the continental shelf north and east of Iceland and mainly on a hard or rough bottom. The sunstar is a predator and scavenger like most starfishes. It eats various sessile or slow moving benthic invertebrates and even other starfishes.