Nodular Sea Star

Overview

The Nodular Sea Star (Echinaster callosus) is a distinctive, relatively uncommon starfish characterized by its warty appearance and five slender, semi-cylindrical arms. It is primarily a nocturnal species that is generally solitary and often goes unnoticed by divers due to its elusive nature.

Distribution & habitat

This species is found throughout the tropical and subtropical western Indo-Pacific, ranging from East Africa and the Red Sea across the Indian Ocean to the western Pacific, including Japan, Australia, and New Caledonia. It inhabits a variety of environments, including coral reefs, rocky areas, and sandy or silty substrates.

Appearance

Reaching a diameter of up to 26 cm, this sea star has a small central disc and five long, cylindrical arms. Its upper surface is densely covered with large, globular, and irregularly arranged warts that vary in color—typically white, pink, red, or violet—often contrasting with the base color of the body. These white warts sometimes form distinct transverse bands, particularly toward the arm tips. The underside is white, featuring ambulacral grooves with tube feet used for movement and feeding. Small, yellowish-green retractable pedicellaria are scattered between the warts.

Biology & behavior

As a nocturnal animal, it is most active at night. Like many other sea stars, it possesses significant regenerative abilities; if an arm is lost, it can regrow, and a detached arm with a portion of the central disc may even regenerate into a new individual. Reproduction can occur both sexually, involving planktonic larvae, and asexually through regeneration.

Feeding

This species is an opportunistic feeder that grazes on organic matter found on rocky and sandy surfaces. It also consumes small sessile invertebrates and detritus.