Invertebrate atlas

Geographical Origin and Habitat: Archaster typicus is widely distributed throughout the tropical Indo-Pacific region. It is commonly found from the East African coast and Madagascar, across the Indian Ocean to the Philippines, Indonesia, southern Japan, northern Australia, and Fiji. It inhabits shallow sandy tidal flats, seagrass meadows, and protected coral lagoons, typically occurring from the intertidal zone down to depths of about 15-20 meters.

Taxonomy: This starfish belongs to the class Asteroidea, order Valvatida, and family Archasteridae. It is distinguished from other sea stars by its highly specialized ability to burrow quickly into sand. It features a flattened body with five tapered arms lined with robust tube feet. Adults reach a total diameter of approximately 10 to 15 centimeters.

Social Behavior: A peaceful, solitary invertebrate that is strictly detritivorous. It spends most of its time buried beneath the surface of the sand. Through its constant movement, it stirs, aerates, and cleans the substrate, which prevents the formation of toxic anaerobic pockets. It poses no threat to any other tank inhabitants.

Coloration and Sexual Dimorphism: The coloration is cryptic, ranging from light grey to sandy brown with darker mottled patterns that provide camouflage against the seabed. The dorsal surface is covered in small, blunt spines. There is no external sexual dimorphism; males and females are identical and can only be differentiated during spawning.

Tank Setup: Requires a well-established marine aquarium of at least 150 liters (approx. 40 gallons). The presence of a fine, soft sand bed (at least 5 to 8 centimeters deep) is absolutely mandatory. Bare-bottom tanks or setups with coarse crushed coral are completely unsuitable and will lead to the animal's death. Secure rockwork directly to the bottom glass pane.

Diet and Feeding: A detritivore that feeds on detritus, uneaten fish food, microalgae, bacteria, and small organisms living in the sand. In very clean or newly set-up tanks, they can easily starve. Supplement their diet by placing small pieces of frozen shrimp or sinking algae wafers near them in the sand bed.

Water Quality: Demands stable marine parameters: water temperature between 22°C and 26°C, pH between 8.1 and 8.4, specific gravity between 1.023 and 1.025, and KH between 8 and 12 dKH. They are extremely sensitive to copper treatments (which are lethal) and rapid changes in salinity. Perform a slow drip acclimation of at least 1-2 hours.

Compatibility and Tankmates: Completely reef-safe. It does not bother corals, clams, or other peaceful invertebrates. Avoid keeping it with starfish predators such as pufferfish, triggerfish, boxfish, and Harlequin Shrimps (Hymenocera picta), which will actively feed on it.

Aquarium Breeding: Breeding in home aquariums is rare but has been documented. They exhibit a unique pseudocopulation behavior where the male climbs onto the female, aligning their arms, followed by the simultaneous release of eggs and sperm into the water column. The larvae go through a complex planktonic stage.

Risks and Diseases: The primary risk is starvation due to lack of organic matter in the substrate. They are highly susceptible to osmotic shock during introduction or from rapid salinity drops, which can cause tissue necrosis (loss of limbs). Any sign of disintegrating arms suggests poor water quality or severe malnutrition.