Jawless mouth, single nasal aperture, only a single pair of external gill openings, no operculum or covering fold of skin. Grayish or reddish brown above, either plain. Variations in color correspond to the color of the sea bottom.
- Bigelow, H.B. and W.C. Schroeder 1948 Cyclostomes. p. 29-58. In J. Tee-Van, C.M. Breder, S.F. Hildebrand, A.E. Parr and W.C. Schroeder (eds.) Fishes of the Western North Atlantic. Part one. Lancelets, cyclostomes, sharks. Sears Foundation for Marine Research, Yale University, New Haven. 576 p. (Ref. 34302) http://www.fishbase.org/references/FBRefSummary.php?id=34302&speccode=2513