The position of the phyla Chaetognatha and Euconodontophylea in the classification of Metazoa

A.P. Kasatkina & G.I. Buryi

Abstract. The types of the fossil Chaetognatha Paucijaculum samamithion (Schram, 1973) found by F.R. Schram from Illinois Pennsylvanian in 1973 and euconodont imprints found by D.E.G. Briggs and others from Carboniferous Granton shrimp bed of Edinburgh are redescribed and reconstructed. Transverse muscular system and apatite composition is observed in different groups of vertebrates and cannot be a ground for undoubted insertion of euconodonts into Chordata. Many similar morphological features (head structure; presence of an intestine and gut diverticle; ventral ganglion; lateral fins flattened in dorso-ventral direction; grasping spines, and spermatophores) allow consideration of euconodonts as animals similar to Chaetognatha. However, such features as terminal position of mouth and anus, and the differences of the tooth apparatus structure give every reason to distinguish euconodonts as an independent phylum, Euconodontophylea. Unique fine structure of the muscular tissue and the structure of the intercellular contacts may indicate early separation of Chaetognatha from the common stem of Metazoa and commencement of original pathway of tissue perfection with preservation of the minimum organ amount. Apparently in Pre-Cambrian, before the skeletization, Chaetognatha and Euconodontophylea had a common ancestor. Both similar phyla belong to a single ancient independent branch, the superphylum Chaetodonta.

Zoosystematica Rossica, 1999, 8(1): 21–26  ▪  Published in print 22 July 1999


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