Fishes of the World
Chapter One
Phylum Chordata
Chordates are placed in the superphylum Deuterostomia. The possible relationships
of the chordates and deuterostomes to other metazoans are discussed
in Halanych (2004). He restricts the taxon of deuterostomes to the
chordates and their proposed immediate sister group, a taxon comprising
the hemichordates, echinoderms, and the wormlike Xenoturbella.
The phylum Chordata has been used by most recent workers to encompass
members of the subphyla Urochordata (tunicates or sea-squirts),
Cephalochordata (lancelets), and Craniata (fishes, amphibians, reptiles,
birds, and mammals). The Cephalochordata and Craniata form a monophyletic
group (e.g., Cameron et al., 2000; Halanych, 2004). Much disagreement
exists concerning the interrelationships and classification of the
Chordata, and the inclusion of the urochordates as sister to the cephalochordate ... read full excerpt from Fishes of the World ebook