The Mysterious Megamouth

The mysterious megamouth makes an appearance – one of only 17. (all images courtesy of Beefy Mance, Nature’s Valley – South Africa)

Meet the megamouth – a shark so unique that when it was first discovered in 1976, a new shark family, genus, and species had to be created. New fish families are uncommon, so the megamouth is in a league of its own. It’s humble about its special status, though, and a little shy. There have only been 17 confirmed reports of this fish that inhabits the Indian, Pacific, and Atlantic Oceans.

While not the most common fish in the sea, the mysterious megamouth is hard to miss. It can reach a length up to at least five metres (17 ft), and true to its name, huge, rubbery lips form a massive mouth that extends beyond its eyes. The outermost surface of the megamouth’s body is blackish brown, while its belly is noticeably white. A white band on the front of its broadly rounded snout is another distinguishing feature.

View of Tsitsikamma National park where the 17th megamouth washed ashore.

So what makes this shark so unique it needed its own family for classification? The megamouth is very primitive. This has confused scientists, because one would think a shark that’s only been known for 26 years would be “advanced.” However, there is nothing advanced about the megamouth. It doesn’t have the tight, streamlined shark body shape that we’re familiar with. Unlike many other deep-water sharks, its skeleton is poorly calcified. This means the megamouth’s body is flabby with soft, loose skin and loosely connected tissues and muscles. Its backbone is also soft and flexible. Because the megamouth spends most of its time in deep water, it doesn’t need a hard backbone: the water pressure holds the shark together.

The megamouth’s less than lithe physique means it is far from an Olympic swimmer. It has poor mobility, which is also due to its asymmetrical tail and lack of keels. Keels provide stability and support to the shark’s body just as they do for ships or aircraft, thereby making sharks better swimmers. The salmon shark and the porbeagle shark, two of the fastest and strongest swimmers, have double-keeled tails, which is unusual among sharks. The megamouth has none.

No fancy food

View of the megamouth’s stark, white belly.

The feeding habits of the megamouth are also simple. It slowly swims around with its mouth gaping, gulping in mouthfuls of water, and then it closes its mouth and squirts the water out its gills. While squirting out the water, the fish swallows trapped plankton – the megamouth’s primary source of food. Plankton are nocturnal feeders – they live in deep ocean waters during the day, and at night they swim to the surface to feed. The megamouth follows this pattern, swimming in deep water by day, shallow by night. They live on a diel cycle, similar to a human’s 24-hour cycle.

Filter feeding – the process of separating out small organisms through mouthfuls of water – is not unknown in the shark world but there are only two other giant filter-feeding sharks in the sea: basking and whale sharks. The basking shark shares the same order as the megamouth, while the whale shark is from the Orectolobiformes, a different order altogether.

The megamouth can reach a length of at least five metres.

The origins of the mysterious megamouth are still debated. One hypothesis claims the megamouth broke away from a single ancestor, the basking shark, many years ago. The second theory is the megamouth branched out much more recently, making it a sister to the mako, white, and porbeagle sharks. According to George Burgess, Director of the Florida Program for Shark Research, the megamouth’s primitive nature suggests the first theory is true. In fact, the megamouth may be the most primitive shark in the order of Lamniformes.

Secret lives

Researchers still have a lot to learn about the megamouth. Because only 17 have been documented, there isn’t much information. For one thing, researchers know nothing about how megamouths reproduce because there haven’t been enough observations on living specimens. Past records of the shark are also hard to come by. The fish have no bone, only cartilage, so there are not many fossils to study. As a result, researchers are still trying to decipher when exactly the megamouth evolved and how many are out there.

View of the megamouth’s namesake: its huge mouth!

The most recent megamouth specimen washed ashore in South Africa in April 2002. Researchers had hoped the encounter would offer clues to the shark’s reproductive system, but the female was an adolescent, and therefore had not conceived any young. Scientists can only hope that when the next megamouth is found, a few more of the missing clues will fall into place.

What you have in your mind?