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Proposing a solution to the Articulata–Ecdysozoa controversy
Author(s) -
Nielsen Claus
Publication year - 2003
Publication title -
zoologica scripta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.204
H-Index - 64
eISSN - 1463-6409
pISSN - 0300-3256
DOI - 10.1046/j.1463-6409.2003.00122.x
Subject(s) - biology , bilateria , phylum , monophyly , sister group , evolutionary biology , zoology , ecology , phylogenetics , paleontology , gene , genetics , clade , bacteria
Recent studies of animal radiation agree on monophyly of the Bilateria, but there is no consensus about the early radiation of the group. Protostomia and Deuterostomia are usually recognized, with two competing theories regarding the division of the Protostomia: one divides them into Spiralia and Cycloneuralia, the other into Lophotrochozoa and Ecdysozoa. The main discrepancy concerns the Arthropoda, which are placed with the Articulata within the Spiralia by the first group, and with the Cycloneuralia within the Ecdysozoa by the second. Here I propose that this discrepancy can be resolved by regarding the Ecdysozoa as the sister group of the Annelida within the Articulata. This implies that segmentation has been lost in phyla such as Nematoda and Priapula, but the Kinorhyncha may show a ‘reduced segmentation’ with serially arranged muscles associated with a ringed cuticle. Morphological, palaeontological and molecular implications of this theory are discussed. While many morphological and palaeontological data can be interpreted in accordance with the theory, the molecular data remain inconclusive.