Prickly Dogfish

Image: New Zealand-American Submarine Ring of Fire 2005 Exploration, NOAA Vents Program
Oxynotus bruniensis

We usually think of sharks as streamlined killers, stalking the ocean in search of their next victim before racing toward them with immense speed and big, toothy jaws.

We don't normally think of them as triangles.

The Prickly Dogfish is a shark found off New Zealand and south-east Australia. They seem to be quite rare, little studied and seldom seen. When spotted, it's usually at depths of 350 to 650 m (1,150 and 2,130 ft) although they have also been reported quite close to the surface and over 1,000 m (3,280 ft) down.

They're only about 75 cm (30 in) long, but they look really odd. With their small head, hunched back and two large dorsal fins, each one mounted on an extra chunk of flesh and armed with a defensive spike. Not to mention all that rough, prickly skin that's so incredibly rough and prickly it sometimes looks quite soft and woolly. But try looking at it head on...

Image: Lia Barrett / Stanley Submarines
Closely related Caribbean Roughshark (Oxynotus caribbaeus)

It's a triangle! The Prickly Dogfish is just one in a genus of five species known as Rough Sharks. All of them have this flat belly and weird, angular sides. It's like they're really good at holding their stomach in, but then it kinda pops out at the sides.

The Prickly Dogfish looks extremely lazy and they probably are. With their huge liver it's likely they can just float effortlessly above the seabed before descending on bottom-dwelling prey. At that point their thick lips, spear shaped upper teeth and blade shaped lower teeth would come into play.

It sounds to me like childbirth is the most strenuous thing these sharks do. They're ovoviviparous, meaning females produce eggs which develop inside her body so that she gives birth to live young. When she's about 65 cm (25 in) long she can give birth to 7 or 8 pups, each one around 24 cm (9.4 in) long! And triangular... It can't be easy.

I wonder if they all fit in a kind of octagon shape?