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Petromyzontidae:1a	Oral area surrounded on top and sides by an oral hood that lacks a marginal papillary fringe; mouth cavity having numerous fimbriate oral cirri; teeth and tongue absent (Figure 17 A)	Petromyzontidae:2
Petromyzontidae:1b	Oral area lacking a hood, being round or oval, disk-like (disk puckered partly closed in some specimens), the disk having a papillary fringe; oral cirri absent; teeth and tongue present (Figure 17 B-E)	Petromyzontidae:6

Click the image to check for a higher-resolution version. Figure 17 [Copyright: American Fisheries Society]

Figure 17: (A) Ammocoete larva, ventral head. dentition of transformed (metamorphosed) lampreys: (B) Lampetra aepyptera. (C) Lampetra appendix. (D) Petromyzon marinus. (E) Ichthyomyzon bdellium. SO - supraoral; LC - Lateral (bicuspid) circumoral; LL - longitudinal lingual lamina; TL - transverse lingual lamina; IO - infraoral; PC - posterior circumoral; MG - marginal (marginal fimbriae drawn schematically).

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