The horned sea star is a large tropical sea star that can reach about 12 inches in diameter. Its thick body has five short, relatively broad arms extending from a well-developed central disc.

The horned sea star is characterized by numerous large knob- or horn-shaped tubercles on its upper surface. These structures are generally darker than the rest of the body, giving it a distinctive silhouette and providing the inspiration for its common name.

Its body coloration ranges from beige to grayish brown, while the knobs may be darker in color. The underside is lighter and bears the tube feet that allow it to move across the seafloor.

The horned sea star is found in tropical waters throughout the Indo-Pacific, from the Seychelles in the Indian Ocean to Australia and Japan, including Southeast Asia and the islands of the western Pacific.

It is particularly common in tropical regions of the western Pacific, including the Philippines and Palau.

The horned sea star mainly inhabits shallow sandy bottoms and seagrass beds. It is particularly common on sandy expanses where marine seagrasses grow, especially in lagoons and on reef flats.

Juveniles inhabit shallow sandy areas rich in marine vegetation, while adults can be found at greater depths, reaching around 100 feet in some regions.

The horned sea star feeds mainly on the thin layer of algae and microorganisms covering the seafloor, as well as organic matter present on the surface of the sediment. It also consumes living or decomposing parts of seagrasses and filamentous green algae.

To feed, it can evert its stomach, bringing it outside its body to digest food directly on the seafloor.

The horned sea star reproduces sexually. Males and females release their gametes into the seawater, where fertilization takes place. A study in the Philippines showed that the breeding season occurs mainly between March and May, when the gonads become more developed.

After fertilization, the eggs develop into larvae that live in the plankton before gradually transforming into young sea stars living on the seafloor.