Scalidophora is a group of marine pseudocoelomate protostomes, consisting of the three phyla Kinorhyncha, Priapulida, and Loricifera. The three phyla have four characters in common — chitinous cuticle that is moulted, rings of scalids on the introvert, flosculi, and two rings of introvert retracts. Their closest relatives are thought to be the Panarthropoda, Nematoda and Nematomorpha; they are thus placed in the group Ecdysozoa.
The two species in the genus Markuelia, known from fossilized embryos from the middle Cambrian, are thought to be stem Scalidophorans.
The group has also been considered a single group, Cephalorhyncha, with three classes.
The group is named after the spines (scalids) covering the introvert (head that can be retracted into the trunk).