Fish o' the Day - bowmouth guitarfish

Gradually catching up on processing my students work in their fish class.  Bear with me, guys.

Visitors to the Georgia Aquarium are usually queued up to see the whale sharks.  Personally, I thought the most fascinating fish in the building was this guy.  Contribution from Jason...
 
Located mostly in the shallow waters near coral reefs and mangroves is an odd-looking fish called the bowmouth guitarfish, Rhina ancylostoma. Looking closely at them, they have the appearance of half shark and half ray. The bowmouth guitarfish‘s flat, broad, arc-shaped head spreads into two distinct triangular pectoral fins. The nostrils, mouth, and gill slits are located on the ventral surface of the head and the eyes and large spiracles on the dorsal side. The jaws are heavily ridged with crushing teeth arranged in wave-like rows. Behind the head, the body tapers into a more streamlined shape, much like that of sharks. There are sturdy ridges of heavy, sharp thorns next to the eyes, in the middle of the back, and above the pectoral fins. It has two large, triangular dorsal fins, the second smaller than the first. The body terminates in a small but powerful caudal fin with an upper lobe that is larger than the lower. Dermal denticles cover the body giving the rough skin a velvety appearance.

The color of bowmouth guitarfish changes with age. Young fish have brown bodies, pale ring-shaped spots covering their pectoral fins, and black bars between the eyes. .The body of the adult is charcoal or pale gray body with small white spots. The face bars fade to dark gray with age, becoming faint and indistinct. Some adults have a bluish coloration. The white ventral side in both adult and juvenile phases provides these rays with protective counter-shading.  Bowmouth are viviparous and are aplacental, generally bearing around 4 pups. While they have been known to grow to lengths of 8 feet, most are closer 6.5 or 7 feet. Bowmouths prefer a relatively shallow habitat with a muddy or sandy substrate, and their primary food sources are crustaceans and mollusks. A quick look at their dentition might allow you to deduce that without ever seeing them in action.  Unlike many oceanic species, bowmouths are not cosmopolitan.  Found mostly in waters of Southeast Asia, they do range into the oceans off East African and are also found along the Indian coastline. 
They’re not currently on the IUCN red list, but there’s a push beginning to see that happen. They’re not fished for their meat, but rather for their dorsal fin. – often the living fish is thrown back into the water to die. In addition, bowmouths sometimes become entangled in gill nets due to their odd shape. 

One interesting idea is being kicked around in taxonomic circles. Bowmouths are often described as prehistoric in appearance, and are considered by some to be a ‘missing link’ between sharks and rays. This belief is based on the ray-like placement of the mouth and gill openings and disc shape of the front part of the body and the shark-like streamlined appearance of the rest of the body and the powerful tail. Is this true? Maybe.