Asterina phylactica is a pentagonal starfish with short blunt arms and a flattened shape.

It grows to a diameter of about 15 mm (0.6 in) and is olive-green with a central brown star-shaped marking, a pale underside, and a clear cut edge between the upper and lower surfaces.

It can be distinguished from the closely related Asterina gibbosa by the fact that it has fewer plates surrounding its mouth, its smaller size and its characteristic colouring.

[3] In Wales, the typical habitat for this species is rock pools on exposed coasts with much encrusting coralline algae.

The eggs have direct development and metamorphose into juvenile starfish which crawl out from under their mother and disperse.