How are the gill openings of tetraodontiform fishes different from those of many other fishes?

Tetraodontiform fishes are distinguished by having small gill openings that are restricted to a relatively short slit on the side of the head. This feature is a result of the evolutionary trend toward reduction in the order, which also affects skeletal elements, fin spines, and mouth size. In contrast, many other fishes—particularly the generalized perciforms from which tetraodontiforms evolved—typically possess larger, more prominent gill openings.123