Metazoa Overview


Abbreviated Dendrogram
Bilateria ├─Deuterostomia └─Protostomia ├─Spiralia │ └─Ecdysozoa = paraphyletic Scalidophora? ╞═Palaeoscolecida ╞═Priapozoa │ ├─Kinorhyncha │ └─┬─Priapulida │ └─ Loricifera └─┬─Nematoida │ ├─Nematoda │ └─Nematomorpha └─Panarthropoda ├─Tardigrada └─┬─Onychophora └─┬─Dinocaridida └─Arthropoda


Ecdysozoan phylaExamples of the phyla of molting animals grouped with arthropods in Ecdysozoa. a Nematoda (Draconema sp.); b Nematomorpha (Spinochordodes tellinii); c Loricifera (Nanaloricus mysticus); d Onychophora (Peripatoides aurorbis); e Tardigrada (Tanarctus bubulubus); f Priapulida (Priapulus caudatus); g Kinorhyncha (Campyloderes macquariae).
Collage and caption from Edgecombe 2009; images courtesy of Martin Sørensen (a, g), Andreas Schmidt-Rhaesa (b, f), Reinhardt Kristensen (c, e) and Gonzalo Giribet (d)

The Ecdysozoa, for our purposes, are treated as bugs > slugs -- a stem group leading to the Arthropoda. However, they are better known as the "molting clade" -- the animal phyla with a cuticle which is molted. Although there is still some suspicion that they might not be a clade, the validity of the Ecdysozoa is coming increasingly to be accepted among workers in this field. Phyla included are the Arthropoda, Tardigrada, Onychophora (which together make up the "Panarthropoda"), as well as the more primitive worm-like and "pseudocoelomate" groups like the Nematoda,  Nematomorpha, Priapula, Kinorhyncha and Loricifera. However, the variability of definitions and uncertainty of the data in this region of phylospace make almost any assignment possible. ATW, revised MAK120415

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