This extremely diverse group of fishes is at the "top" of the tree, saving "the best for last." They include the group Smegmamorpha, which is a great name (DO NOT look up smegma). This group includes a ton of families.
This order of deep sea fishes is known to have relatively thin skull bones. That's no good for a concussion! They also tend to have roundish bodies.
All species in this order share an osteological feature called Jakubowski's organ. It is a modification of the supraorbital and infraorbital sensory canals (what they're sensing, I do not know).
No, this isn't the character from Finding Nemo. These fishes have a compressed, deep body plan and have highly distensible jaws. There are a few other distinguishing features but most are osteological so we won't mention them here.
This order is made up of two suborders: Gasterosteoidei and Syngnathoidei. There are a few skeletal characteristics, and many species have dermal plates. Let's take a look!
There is one family, Synbranchidae. They not only lack pelvic fins but pectoral fins as well, the dorsal and anal fins are vestigial, and the caudal fin is small to absent. The eyes are small, with some species having them below the skin. Most species can breathe air via suprabranchial pouches. They also lack gasbladders.
No, you won't find any of these fishes driving a postal truck! "Mail" refers to armor, and these fishes have a spinous process extending from one of the infraorbital bones. Almost all of these fishes have spines or bony plates.
There's not really many descriptive characters, so I guess you'll just have to go take a look at the page yourself.
Who wouldn't recognize a flounder, trying to remain camouflaged on the seafloor, with both of its eyes strangely located on only one side of its body? This weird order of fishes has discovered a unique benthic lifestyle. Instead of being dorsoventrally flattened like many other groups, the flatfishes are laterally flattend and lay on their side in the sand. They have adapted to this lifestyle by moving the sand-side eye over to the upper side, a transition that is observable from larva to adult. Interestingly, most families lay on either their left or right sides, but usually not a mixture (there are some exceptions).
This is one crazy group of fishes! You've got round fishes, flattened fishes, even box-shaped fishes! There's even fishes that don't know how a fish is supposed to look! Many species have modified scales, which are spines or spikes. The teeth are also usually modified for crushing their food. They are also unable to protrude their jaw, as the premaxilla is fused to the maxilla.