Remora, Remora remora (upper image)
The flat ridged disk on the top of the remora's head allows the remora to attach to other animals by suction. The suction pad is not an entirely new development in remoras: it's actually a modified dorsal fin. Photo taken at Jardines, Playa del Carmen, Quintana Roo, Mexico.
Manta ray with remoras (lower image)
By sticking close to larger fishes, sharks and marine mammals, remoras have easier access to scraps of food and protection. Photo taken at Vakarufalhi, Maldives.
Cuvier's Bichir, Senegal Bichir, Dinosaur Eel Polypterus senegalus
Lower image shows shape of the modified swim bladder that serves as unevenly paired lungs.
Also known as Senegal bichir or gray bichir is an example of a modern fish that possesses both derived and primitive features. Derived features include the bichir's multiple dorsal fins.
Primitive features include a swim bladder that has been modified into a lung-like structure and ganoid scales. In nature, they are nocturnal carnivores that live in slow-moving turbid water. [add] They are popular aquarium fish for several reasons - their ability to breathe air makes them forgiving about oxygenation but prone to escape unless the tank is closed - they are known to come out at night - they sometimes eat other aquarium-mates and bite each other although - their scales protect them - they have a keen sense of smell for food when it's added into the tank - and many enjoy the primitive aspect of this animal. Define lung. Check with aquarist.
Upper image courtesy of G. J. Reclos, www.mchportal.com
Lower image courtesy DigiMorph.
Spinner dolphins spinning.
Cuvier's Bichir, Senegal Bichir, Dinosaur Eel