Manta Rays

Once again I've had the good fortune to visit the Manta Rays of San Benedicto Island, in the Pacific off the coast of Mexico. Thanks again to Gregory Colbert, his film crew and friends, and the crew of the Nautilus Explorer for another wonderful trip.
I haven't been able to find a reference to the tubes just above the corners of the manta's mouth pictured below. Thanks to Sten Johansson of the Nautilus Explorer for the photos and for pointing out this interesting feature. Please comment if you can identify these structures, a reference or link to the literature would be especially welcome!