The megamouth shark
Megachasma (Figs. 1, 2), just entered the large reptile tree (LRT, 1648+ taxa; subset Fig. 3) between the primitive sharks Cladoselache (Late Devonian) + Chalmydoselache (extant) and all higher sharks + rays.
Megachasma pelagios (Taylor, Compagno and Struhsaker 1983; up to 5m) is the extant megamouth shark, a deep water filter feeder. In the LRT Megachasma nests between Cladoselache and higher sharks (Fig. 3). It is the basalmost shark with single cusp teeth. The rostrum extends only slightly over the mouth with anteriorly-oriented nares, as in more primitive taxa.
Taylor LR, Compagno LJV and Struhsake PJ 1983. Megamouth – a new species, genus, and family of lamnoid shark (Megachasma pelagios, family Megachasmidae) from the Hawaiian Islands. Proceedings of the California Academy of Sciences. 43 (8): 87–110.