Claim: Pelvic fin structures can be extremely specialized in actinopterygians, with Gobiids and lumpsuckers modifying their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls.
Evidence: Gobiids and lumpsuckers modify their pelvic fins into a sucker disk that allow them to adhere to the substrate or climb structures, such as waterfalls. Pelvic fin structures can be extremely specialized in actinopterygians.