What are the Ecdysozoa?
Ecdysozoa is a proposed super-grouping of eight animal phyla (out of approximately 37) — Arthropoda, Onychophora, Tardigrada, Kinorhyncha, Priapulida, Loricifera, Nematoda and Nematomorpha. It is a controversial grouping, but a large genetic study in Nature in 2008, “Broad phylogenomic sampling improves resolution of the animal tree of life,” strongly supported the Ecdysozoa as a natural category. The group was originally proposed as the result of genetic studies using 18S ribosomal RNA genes in 1997. The primary characteristic the Ecdysozoa share is the molting of a three-layered cuticle in a process called ecdysis (from whence the group gets its name). Another shared feature is the absence of locomotory cilia in reproductive cells — the sperm are amoeboid. Ecdysozoa embryos do not undergo spiral cleavage, while other protostome embryos do. The Ecdysozoa are all protostomes, one of the two major groups of animals, the other being deuterostomes. Ecdysozoa is a proposed superphylum wi
