Ecdysozoa
- Pronunciation
- /ek-DIS-oh-ZOH-uh/
- Category
- Taxonomy
- Singular
- Ecdysozoa
Definition
A major clade of protostome animals united by the shared trait of —the periodic shedding of a cuticular to permit growth. The clade encompasses Arthropoda (including insects, arachnids, and crustaceans), Nematoda, and several smaller (Onychophora, Tardigrada, Kinorhyncha, Loricifera, , Priapulida). Proposed initially from morphological analyses and subsequently strongly supported by molecular (18S rRNA and later multi-gene datasets). Ecdysozoa represents one of the two primary divisions of Protostomia, the other being Spiralia; together they comprise the bulk of bilaterian animal diversity. The synapomorphic varies in composition—chitinous in , collagen-rich in —but the molting process is regulated by conserved hormonal across the clade.
Etymology
From Greek ékdysis (stripping, shedding) + zoa (animals), referring to the shared molting process.
Example
Insects and arachnids, though divergent in body plan, are both ecdysozoans: a larva and a nymph each must their rigid multiple times to reach adulthood, reflecting the deep evolutionary of that unites these groups within Ecdysozoa rather than with mollusks or annelids in Spiralia.
Related Terms
Usage Notes
The rank of Ecdysozoa has been variously designated as clade, superphylum, or unranked depending on systematic convention; modern practice increasingly treats it as an unranked clade to reflect phylogenetic rather than Linnaean hierarchy. The composition is stable for major , though relationships among , tardigrades, and onychophorans relative to remain actively debated (the 'Panarthropoda' hypothesis groups Onychophora+Tardigrada+Arthropoda). Ecdysozoa is not synonymous with 'arthropods and worms'—the grouping is strictly phylogenetic, not ecological or morphological. Contrast with Spiralia (protostomes lacking , including mollusks, annelids, and platyhelminths). The term is capitalized as a formal taxon name.