Remipede

Image: Simon Richards

Oh no! Don't tell me centipedes have made it into the sea as well?

Not exactly. They may look a lot like centipedes, but Remipedes are actually crustaceans. The name means "oar foot", because these little beasts swim around on their back by waving several dozen legs.

The amazing thing is that they also have a venomous bite! Some of their mouthparts have evil claws for injecting venom or digestive enzymes into prey such as shrimps. No other crustacean is known to do this, but it's just like a centipede!

You might now be worried that you have yet another thing to worry about when you travel to your holiday home in the mermaid city of Atlantis, but you needn't. For two reasons:

One, Remipedes are tiny! There's a family of them called Godzilliidae because of a giant species who was... 4 cm (1.6 in) long. Others are just 1 cm (0.4 in).

The other reason is where they live. Remipedes have horrible homes called anchialine caves. These are coastal caves which contain both sea water and spring water.

Salt water is heavier, so the fresh water floats on top and in between is a hypoxic layer which is where oxygen is traded in for bacteria and various toxins poisonous to most life. I prefer oxygen, myself. I'm very conservative like that

Remipedes live in the lower, marine layer, which is less poisonous but still has a dearth of oxygen. Most completely lack eyes, vision being of little use in their dark abodes. More useful are their long antennae and sensory hairs running along their body. All Remipedes thus far studied have been hermaphrodite, presumably an adaptation to small population sizes. Not much else is known about them.

Image: Thomas M. Iliffe

We know a lot more than we used to, though! For many years Remipedes were known only from fossils some 300 million years old. Back then they could get almost 80 cm (2 ft 7 in) long and had large compound eyes!

Since 1979, 24 living species have been discovered in the Caribbean, Australia and the Canary Islands off north-west Africa. It's now thought that insects evolved from crustaceans and that Remipedes are more closely related to insects than any other crustacean.

So the poor old Remipede appears to be a relic from a bygone era. We don't know much about their ancient ancestors, but today they have been banished to the ugly, stinking corners of the world, scurrying beneath a firmament of toxic gases and bacteria. They are the IT department of Crustacea ltd.