I’ve seen a few different videos of sharks with their mouths open wide. The side of the mouth has these vertical white structures running from top to bottom with dark spaces in between. They look kind of like bleached bone, which makes no sense.
What are these things, and what are they for? When I first saw them in a basking shark video, I thought it was light shining through gill slits, but
More specifically, they are the gill (or branchial) arches in all 3 vids, the rakers are only seen in the basking shark ones, tiger sharks don’t have them.
Why don’t these bony* arches get infested with parasites (e.g. barnacles)? It seems like an ideal place for a filter-feeder to attach. There’s a steady flow of water (to feed the gills). You get scraps (and blood) every time the shark has a meal. Or to put it another way, why do fish and sharks have exposed bony* structures in their mouth while in a mammals mouth the only exposed bone-like structures (i.e. teeth) are coated with a hardened material?
*Yes, I know it’s cartilage rather than bone, but I don’t know why cartilage would be more resistant than bone (to be fair, I know very little about biology beyond the basics I learned in grade school).
