Indo-Pasific Sand Sea Star

Archaster typicus

Taxonomy

Kingdom: Animalia 

Phylum: Echinodermata

Class: Asteroidea

Order: Valvatida

Family: Archasteridae

Genus: Archaster

Habitat & Distribution :  Indo-Pasific Ocean

Diet: Plankton, Algae, and detritus

Size: Up to 12 - 15 cm

Lifespan: 3 - 5 Years

Deskription

Archaster typicus, commonly known as the sand starfish or sand-sifting starfish, typically possesses five long, slightly tapering arms that end in sharp points; however, individuals with three, four, or even six arms are occasionally found. Adapted for life on sandy seabeds, it buries itself in the sediment during high tide and moves across the surface during low tide. Its coloration is generally gray or brownish, featuring a variety of dark and light patches that sometimes form a chevron (inverted V) pattern, while the underside is pale. The body is somewhat inflated, with a whitish madreporite located near the center of the central disc. Small protective plates covering the upper surface of the arms are arranged in neat, parallel rows—a feature that distinguishes it from Astropecten polyacanthus, a species with similar habits and coloration. Its spines, which form a fringe around the body's edge, are short, flattened, and relatively blunt.

Behavior

Archaster typicus using pointed tube feet (lacking the suction cups found on reef starfish) to move sand grains aside. This allows them to sink and disappear into the sand within a few minutes. Depth: They typically bury themselves just beneath the sand's surface (about 1–3 cm deep). This behavior serves as a primary defense against natural predators—such as seabirds, large fish, and crabs—during both high and low tides.

Reproduction

Unlike many other echinoderms which release eggs and sperm randomly into the water, Archaster typicus perform coordinated mating rituals. The male starfish will climb and be on top of the female starfish, aligning their arms (pseudocopulation). This stacked position can last for several days. When the female releases eggs, the male will immediately release sperm at the same time.

Communication & Perception 

The most critical form of communication for *Archaster typicus* occurs during the mating season. Mature female starfish slowly release chemical substances—specifically sex pheromones—into the water column. Using chemical sensors (chemoreceptors) distributed along their tube feet and the tips of their arms, starfish can detect the presence of these pheromones from a distance. This signal triggers the starfish to move more actively in search of the scent source, enabling them to locate the female or other starfish.

Predator

Pufferfish, Harlequin Shrimp, and Triggerfish