Mediaster aequalis has five stumpy arms, occasionally four or six. This species grows to a diameter of up to 20 cm. The upper surface is bright red while the under surface is an orangey-red coloured. The tube feet are red.
Mediaster aequalis is omnivore,a predator and will scavenge for dead animals and detritus. As well as feeding on algae, it preys on tunicates, sea pens, sponges, bryozoans, brachiopods and polychaete worms. In its turn it is hunted by the larger morning sun star.
Similiar to Pteraster tesselatus, Dermasterias imbricata, and Patiria miniata.They have similar shapes but do not have the large marginal plates.