The biscuit sea star is easily recognizable by its thick body and almost pentagonal shape. Its five arms are very short and barely defined, giving the animal a compact silhouette reminiscent of a biscuit.

Its upper surface is made up of large, clearly visible calcareous plates, much more prominent than those of many other sea stars. These plates also form a broad rim around the entire body. Its coloration is generally orange-red, but it can also be brown or yellowish, while its underside is lighter.

The biscuit sea star averages about 4 inches in diameter, but the largest specimens can reach up to 8 inches in diameter.

The biscuit sea star is found mainly in the temperate to subtropical waters of the eastern Atlantic Ocean and the Mediterranean Sea. It occurs notably in the Bay of Biscay, along the western coast of Africa as far south as Senegal, as well as in various parts of the Mediterranean, particularly the Adriatic and Tyrrhenian seas.

It has also been reported in the Red Sea, where it reached the region through the Suez Canal.

The biscuit sea star primarily inhabits soft seafloors made up of sand, mud, or gravel, generally at depths where seagrass beds no longer grow. It can also live on rocky bottoms and steep reef slopes.

The biscuit sea star is generally found from a few dozen to about 330 feet deep, but it can also occur at greater depths, reaching several hundred feet and even as deep as about 3,280 feet.

The biscuit sea star is a predator that can feed on black corals. It has notably been observed consuming the living tissues of the black coral (Parantipathes larix) in the Mediterranean.

The reproduction of the biscuit sea star is still poorly understood. Like other sea stars, it presumably reproduces sexually, with males and females releasing their gametes into the water, where fertilization takes place. The eggs then develop into planktonic larvae that undergo metamorphosis before becoming young sea stars.