There are papillae on the roof of the mouth and the edges of the gill arches.
They attach themselves to the bases of the gill arches of their hosts.
Originally it was the lower of two cartilages which supported the first gill arch (nearest the front) in early fish.
They are grouped together because of common features in the structure of their gill arches.
They have narrow heads, and 16-24 tooth-rakers on their third gill arches.
In fish, the first gill arch forms the support for the jaws including the spiracle.
The heart of a fish is a simple muscular structure that is located between the posterior gill arches.
They also have a large, accessory breathing organ composed of modified gill arches.
These two blood streams remain mostly separate as they flow through the ventricle leading to the gill arches.
Scattered, sparse papillae are inside the mouth and on the edges of the gill arches.