FIG. 4 in False teeth: conodont-vertebrate phylogenetic relationships revisited

FIG. 4. — Schematic frontal and cross sections of anterior end of a conodont animal compared with a cephalochordate and selected chordates. The left side of the animals shows dorsal surface features and muscle segmentation and the right side is cut away to show internal features at the level of the branchial region (if present): A, generalized conodont showing the position of conodont elements (association of structures based on Briggs et al. 1983, which is still highly imaginative with little reality beyond the general shape: note the diametrically opposed symmetry of apparatus to any vertebrate); B, amphioxus Branchiostoma lanceolata (Pallas, 1774); note that the notochord reaches into an anterior extension, but not the neural cord and not the dorsal "fin" (see 9) (after Bracegirdle & Miles 1978 and Parker & Haswell 1921); C, hagfish Myxine glutinosa Linnaeus, 1758 (after Dean 1899 and Marinelli & Strenger 1954); D, lamprey Lampetra fluviatilis (Linnaeus, 1758) (after Marinelli & Strenger 1956: figs 6, 10, 17, 36, 42); E, shark Squalus sp. (frontal section after Liem et al. 2001: fig. 18-2C). 1, muscular "cone"; 2, conodont apparatus (after Aldridge 1987: fig. 1.3 and Norby 1976); 3a, V-shaped myomeres; 3b, W-shaped myomeres; 4, medial tube; 5, notochord; 6, nerve cord; 7, velum (oral hood); 8, gill; 9, fin-ray box; 10, mouth; 11, pharynx; 12, branchial duct; 13a, nasal sacs; 13b, nasohypophysial opening (NB: not 13 for both as in Donoghue et al. 2000); 13c, nares; 14, hypophysial duct; 15, hypophysial sac; 16, gill arch; 17, eye; 18, mandibular arch with odontodes (teeth); 19, gill chamber; 20, external gill slit; 21, oesophagus; 22, spiracle; 23, brain; 24, anterior margin of pharynx; 25, hyoid arch.