Astropecten platyacanthus is a species of sea star of the family Astropectinidae. It is found only in the Mediterranean Sea living on mobile seabed (sand, mud or gravel) remaining largely buried under the sediment during the daytime. It comes out in late afternoon and is active throughout the night. It can be found at depths between 3 and 200 feet, but is more frequently found in mixed coarse sand and mud at depths of 3 to 12 feet.
This starfish has narrow and high superomarginal plates, laterally covered with scales and small spines on the vertical face. Each plate is equipped with one strong spine, irregularly shaped and very sharp. The spines are usually yellow or orange but rarely white. In some specimens the superomarginal plates are totally devoid of spines; in populations in certain regions of the Mediterranean, this is fairly common. The maximum number of superomarginal plates on each arm is 48; the average is between 29 and 43, depending on the sea star’s size.
The inferomarginal spines are long, flat and pointed. The arms can be wide or narrow and the aboral (back) side can have variable coloration (dark brown, olive green, pink-brown or bluish-gray). The oral side (with the mouth) is usually yellow-brown. The adult size if about 3.5 to 4.7 inches in diameter, but can sometimes measure up to 9.5 inches.
It is a very hard sea star to identify due to several similarities with other Astropecten species found in the Mediterranean. The easiest way to tell it apart from other species are by its superomarginal spines and size. The spines of this species are usually placed farther from the inside edge of the plates than with other species.
Young specimens of A. platyacanthus can often be confused with A. jonstoni for the appearance and the color, but it is always easy to distinguish them by very different superomarginal plates and superomarginal spines.
Image Caption: Astropecten platyacanthus. Credit: Rpillon (CC BY-SA 3.0)