OBO_REL:part_of (UNDECLARED) anatomical cluster caudal principal ray set Anatomical cluster including all segmented-and-branched rays plus one unbranched but segmented ray located at the leading margin in each lobe of the caudal fin (Hubbs and Lagler, 1947) and that associates with endoskeletal elements such as hypurals and hemal spines of preural centra 1 and 2 (Arratia, 2008). Caudal principal rays are counted from the dorsalmost one ventrally. Caudal principal rays are unpaired median bones. In basal teleosts the number of caudal principal rays is about 20. A decreasing of the number of the branched-and segmented rays is observed in more advanced teleosts (see Schultze and Arratia, 1989; Arratia, 1991, 2008). The presence of marginal principal caudal rays as long or longer than the branched-and-segmented principal rays is a synapomorphy of teleosts (Arratia, 2008, 2009). TAO:0002164 branched caudal rays caudal principal lepidotrichia teleost_anatomy caudal fin skeleton