KEY TO SUPERCLASSES,
CLASSES AND SUBCLASSES
1a Jaws and paired fins absent; front of head with 3 pairs of fleshy barbels
surrounding the mouth; eyes rudimentary; body eel-like .................... .
....................................................... Superclass AGNATHA, p. 32
1b Jaws present; paired fins present (except in some eels); barbels absent in
most families; eyes well developed in most families ........................... .
................ Superclass PISCES (GNATHOSTOMATA) ................. 2
2a Five to seven outer gill openings on each side on head (no gill cover or bony
operculum covering the gills) ....................................................... .
..... Class CHONDRICHTHYES (Subclass ELASMOBRANCHH), p. 41
2b A single gill opening on each side of head, the gills being covered with a
gill cover or bony operculum ..................................................... 3
3a Skeleton of calcified cartilage only (no bone); fertilisation internal, the
male with paired intromittent organs (claspers) on the pelvic fins; upper
jaw fused to skull; teeth fused into 3 pairs of tooth plates ................... .
....... Class CHONDRICHTHYES (Subclass HOLOCEPHALI), p. 144
3b Skeleton (of adults) mostly of bone; fertilisation internal or external, but
no paired intromittent organs on pelvic fins; upper jaw not fused to skull;
teeth separate in most families ........... Class OSTEICHTHYES, p. 149
31