Scalidophora is a group of marine pseudocoelomate invertebrates, consisting of the three phyla Kinorhyncha, Priapulida, and Loricifera. The members of the group share a number of characteristics, including introvert larvae and moulting of the cutitle (ecdysis). Their closest relatives are thought to be the Panarthropoda and Nematoda; they are thus placed in the group Ecdysozoa. A pseudocoelomate is an animal like a roundworm or rotifer. ... Invertebrate is a term coined by Jean-Baptiste Lamarck to describe any animal without a spinal column. ... Jump to: navigation, search Phylum (plural: phyla) is a taxon used in the classification of animals, adopted from the Greek phylai the clan-based voting groups in Greek city-states. ... Orders Cyclorhagida Homalorhagida Kinorhyncha (Gr. ... Priapulida (priapulid worms, or penis worms) are a phylum of marine worms with an extensible spiny proboscis. ... Jump to: navigation, search Loricifera is a small phylum of marine sediment-dwelling animals with about a dozen known species. ... Ecdysis is the molting of the cuticula in arthropods and related groups (Ecdysozoa). ... Panarthropoda is a taxon combining the Phyla Arthropoda, Tardigrada and Onychophora. ... Classes Adenophora    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria The roundworms (Phylum Nematoda) are one of the most common phyla of animals, with over 20,000 different described species. ... The Ecdysozoa are a large group of protostomian animals, erected by Aguinaldo in 1997 primarily based on 18s rRNA data. ...

The two species in the genus Markuelia, known from fossilized embryos from the middle Cambrian, are thought to be stem Scalidophorans. Markuelia denotes a genus of fossil worm from the Middle Cambrian period that encompasses two known species, Markuelia hunanensis and Markuelia secunda, which are presumably the closest known relatives to three modern taxa of bilaterian animals: the Loricifera, Kinorhyncha and Priapulida. ... The Cambrian is a major division of the geologic timescale that begins about 542 million years before the present (BP) at the end of the Proterozoic eon and ended about 490 million years BP with the beginning of the Ordovician period. ...

The group was formerly considered a single phylum, Cephalorhyncha, with three classes.