This species is active and easy to find during the night but also during the day, especially in early morning and late afternoon.

It has narrow and high superomarginal plates, laterally covered with scales and small spines (on vertical face).

Every superomarginal plates is equipped with one strong spine, usually sharp but irregularly shaped, slightly flattened laterally, often yellow or orange but rarely off white.

It is distinguished from Astropecten bispinosus mainly for the superomarginal spines far from the inside edge of plates and they leave on top, on the base of them, a small bare area.

Another important feature of Astropecten platyacanthus is that the superomarginal plates are laterally, on vertical face, covered with scales and small spines rather than nude.