The Amphiura tenuis species exhibits a distinct concave shape in both the dorsal and ventral sides of its central disc, particularly between the arms. The underside of the disc lacks any covering, and it features a large and circular madreporite. The adoral shields are sizable but do not meet in front of the oral shields. The oral plates are short and slim. At the tip of the jaw, there are two infradental papillae and on each side, there is one lateral papilla, situated distally and separated from the infradental papilla by a noticeable gap. A large scale on the oral tentacle is visible between the infradental and lateral papillae, while there is an absence of a tentacle scale.