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Sharks of this family are easily recognizable by the very firm half-moon-shaped (technically lunate) caudal fin, with lower lobe but little shorter than the upper, in combination with large awl-like or blade-shaped teeth, and with gill openings larger than any other Gulf of Maine shark except the basking shark. Their tail fins, in fact, recall the tails of such bony fishes as the mackerel tribe or the swordfish, in outline, likewise in firm texture, hence their common name. The basking shark also has a caudal fin and peduncle of this same sort, but its teeth are minute and very numerous, and its gill openings are so long that those of the two sides nearly meet on the lower surface of the throat.
Other diagnostic features are that they have an anal fin; that their caudal peduncle is expanded as a prominent longitudinal keel on either side; that their dorsal fins are not preceded by spines; and that the inner margins of their gill arches do not have horny gill rakers.