How does the incomplete series of bones beneath the eye distinguish atheriniform fishes?

Atheriniform fishes are distinguished by an incomplete series of infraorbital bones beneath the eye, as they possess only the first (lachrymal) and last (dermosphenotic) bones of this series. This structural characteristic is one of several features that differentiate them from typical acanthopterygians, which generally exhibit more complex systems of bones and ligaments in the head and jaw.1