The karyotypes of two sharks and cellular DNA contents of four sharks in the order Carcharhiniformes were studied and determined to be as follows: Prionace glauca: 2n = 86, M-SM = 30, ST-A = 56, FN = 116, DNA = 8.6 pg/cell; Sphyrna lewini: 2n = 86, M-SM = 20, ST-A = 66, FN = 106; Carcharhinus obscurus: 2n = ca. 78, M-SM = ca. 20, ST-A = ca. 58, FN = ca. 98, DNA = 6.0 pg/cell; C. plumbeus: 2n = ca. 74, M-SM=ca. 18, ST-A = ca. 56, FN = ca. 92, DNA = 6.0 pg/cell; C. galapagensis: DNA = 8.5 pg/cell.
These carcharhinid sharks showed a smaller size and range of chromosomes compared with those of triakidid and scyliorhinid sharks. Smaller sized meta-, submeta- and subtelocentric chromosomes in the carcharhinid sharks may have resulted from pericentric inversions. From karyological features, Sphyrna lewini shows close affinities to sharks in the family Carcharhinidae, supporting a recent cladistic analysis of the order Carcharhiniformes in which the Carcharhinidae included the genus Sphyrna.