Cow Shark

Image: Peter Southwood

Cow Shark. Cow. Shark.

This is a most unlikely alliance.

Image: Derek Keats

Cow Sharks are 4 species of large, meat-eating fish with sharp teeth. They have no udders, legs or even horns. The whole Cow thing doesn't go at all far.

They belong to a family called Hexanchidae, which comes from the Greek for "six arches", referring to the fact that some Cow Sharks have six gill slits. This is unique since just about every other shark in the world has only five gill slits. However, two of the Cow Sharks don't have six gill slits. They have seven. This is called "showing off."

Video: Rooftop Pictures

The biggest Cow Shark is the Bluntnose Sixgill Shark (Hexanchus griseus). It has six gills! And a blunt nose. Finally - accuracy.

They can reach a length of 4.8 metres (15.5 feet), though most individuals are somewhat smaller. They've been found in deep, offshore waters all over the world, where they spend the day near the ocean floor at depths of around 2,000 metres (6,500 ft) and swim up toward the surface at night to hunt.

Image: Dan Hershman
Cow Sharks have fluorescent eyes!

The Bluntnose is usually quite slow and sluggish but they can turn on the speed when they need to chase down prey. They'll eat pretty well anything available in the area, including large fish, squid, other sharks or crustaceans. They'll also scavenge carrion if they can find it. It's a good deal because they can be slow, sluggish AND well-fed. They have carrion, we have the butcher's shop (where you'll find bits of cows, ironically enough).

The Bluntnose, in common with other Cow Sharks, is civilised enough to use a knife and fork. Sort of...

Image: Ross Robertson

Cow Sharks have really cool teeth (cool for them, not so much for the thing they're biting). The upper teeth are long and slim, like the prongs of a fork, while the lower teeth are like saws for cutting through flesh. Those lower teeth are sometimes called "comb-shaped", but it would be one of those metal combs that hurt. And it would be a James Bond comb which is actually a deadly weapon in disguise.

Image: Robertson, D Ross

Cow Sharks don't have a large number of teeth, but the Bluntnose gets by very well with a dozen serrated razor blades in its lower jaw.

Image: Jean-Lou Justine

Belonging to the same genus as the Bluntnose, the Bigeye Sixgill Shark (H. nakamurai) also has six gills plus enormous eyes. They reach 1.8 metres (6 ft) long at most and spend much of their time at depths of about 600 m (2,000 ft).

That does it for the Sixgills. Now for the Sevens!

Image: NOAA/NMFS/SEFSC

The Sharpnose Sevengill Shark (Heptranchias perlo) is the only species in the genus Heptranchias, a name which refers to their seven gill slits. It only reaches a maximum length of 1.4 m (4.6 ft), making it the smallest of the Cow Sharks. It compensates for this deficit by being a particularly aggressive and voracious predator. Just like Napoleon or a 2-year-old.

Video: piscesdivers

And after the Sharpnose what else could possibly follow but the Broadnose Sevengill Shark (Notorynchus cepedianus). You shall know them by their noses. This species may reach up to 3 metres (10 ft) long and tends to live in shallower waters than the others.

Image: Robertson, D Ross

They have a particularly inelegant face. It reminds me of a sausage for some reason. It's a sausage-faced shark. The genus name, Notorynchus, means "back snout". I have no idea what this means. What's sausage-face in Greek?

As is the norm among sharks, Cow Sharks are slow to reproduce. Female Bluntnose Sixgills can take 20 or 30 years before they're old enough to reproduce and it's thought their total lifespan may be some 80 years. Something more unusual about that particular species is a single litter can number over 100 pups! That's a LOT! By contrast, the Sharpnose Sevengill will have more like 10 or 20.

Also the Broadnose will have about 80 pups and the Bigeye little more than 10. I'm telling you, there's something about those noses. If you have a face like a sausage, you'll have a lot of pups.

Video: Earth Touch

Whatever kind of face they have, these Cow Sharks are all doing something right. The Hexanchidae family dates back 200 million years to the Triassic period and there are dozens of species that have died out. The few that survive to this day have come a long way.

Just keep them away from actual cows.

Those guys are vicious.