The spiny sand seastar (Luidia quinaria) is a species of starfish in the family Luidiidae.

There are three subspecies:[1] Luidia quinaria has a small central disc and five long slender arms fringed with short spines.

The general colour of the aboral surface is grey with contrasting pink or orange margins to the arms.

Examination of the stomach contents of both starfish showed that Luidia quinaria largely fed on other echinoderms, in particular the brittle star Ophiura kinbergi, which formed more than half of the diet.

The other starfish largely consumed molluscs, including the snail Voorwindia paludinoides and the clam Alvenius ojianus.