An oceanrider is proficient with light and medium armor, and with shields (but not tower shields).
This alters armor proficiency.
A Medium oceanrider can ride either a seahorse or an orca (unlike most orcas, this one starts at size Large with none of the other level 7 abilities until level 7) instead of the normal options, while a Small oceanrider can ride a dolphin.
This alters mount and replaces expert trainer.
Pathfinder Campaign Setting: Aquatic Adventures © 2017, Paizo Inc.; Authors: Amber E. Scott and Mark Seifter.