The African red-knobbed sea star is a large, robust sea star that can reach about 12 inches in diameter. Its thick body has five relatively short, broad arms separated by well-defined grooves.

Its most spectacular characteristic is the numerous red conical tubercles that rise from the upper surface of the central disc and arms. These knobs are connected by a network of red lines that contrasts with the cream to light gray coloration of the body, giving it a particularly striking appearance. The tubercles are absent from the lateral margin of the disc but may occur around the tips of the arms. The underside is generally red, with lighter ambulacral grooves.

The African red-knobbed sea star is found mainly in the tropical waters of the western Indian Ocean, along the tropical coasts of East Africa, particularly Kenya, Tanzania and Mozambique, as well as around Madagascar, the Seychelles and the Comoros. Its range extends northward to India and the Andaman Sea. An isolated population is also known from northwestern Australia.

In the tropical Pacific, it is replaced by closely related species of the same genus, including the horned sea star.

The African red-knobbed sea star mainly inhabits sandy bottoms in lagoons and shallow coastal areas. It also occurs in seagrass beds, where it moves across the surface of the sediment in search of food.

The African red-knobbed sea star generally lives in calm waters rich in organic matter and can be observed from very shallow water to depths of several dozen meters.

The African red-knobbed sea star feeds mainly on material covering the soft bottoms where it lives. It consumes the thin layer of algae and microorganisms covering the sand, as well as small particles and organic debris that accumulate there.

Like other sea stars, it can evert its stomach to digest larger food items directly on the substrate.

The African red-knobbed sea star reproduces sexually, and individuals are generally either male or female. During reproduction, adults release their gametes into the seawater, where fertilization takes place in the open water. The sea star then adopts a characteristic position, raising its body above the seafloor while keeping its five arms partly in contact with the substrate.

The fertilized eggs develop into planktonic larvae that remain in the water column for several days before settling on the seafloor and beginning their metamorphosis into young sea stars. Reproduction takes place particularly during spring, and spawning appears to occur more frequently around the full moon.