Arrow Crab

Image: NOAA Photo Library via Flickr

These fellows just make me smile, I love 'em! Although I must admit that I was quite surprised at the intimidating guy on the left there! They usually remind me of Bert from Sesame Street. Then again...

Arrow Crabs are coral reef inhabitants with 8, extremely long legs and tiny pincers at the end of 2 extremely long arms. Then there's the utterly adorable pointy head with eyes popping out partway up.

To me, they look extremely intelligent and intellectual. I bet they were one of those kids at school who had a massive pencil case full of everything they could ever need, including 6 different kinds of ruler and a dozen pens in case someone like me asked if I could borrow one.

Image: baltus15 via Flickr

Their size varies, but it seems the total legspan can reach about 20 cm (8 inches) or thereabouts. They are also territorial and may be aggressive to intruders. I myself remember getting thwacked by one of those rulers if my hand ventured too close to that exalted pencil case...

Arrow Crabs are mostly nocturnal scavengers, eating pretty much anything they come across. They might also hunt worms and some of them will even fastidiously groom their limbs for algae and such. Others, like the Decorator Arrow Crab, go the other way and pick up bits of debris to stick to themselves and serve as camouflage.

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Image: Chika via Flickr

To mate, the male simply hands over a little packet of sperm to the female. I can't help but think that this activity can only occur after the male has impressed her with his knowledge of geometry and calculus. They just look like they really value the rigour of mathematics and other high-minded pursuits.

The female carries the eggs under her abdomen until they hatch and the larvae swim off to join the plankton at the water's surface. They metamorphose later to rejoin the seabed and become the local pointy-head boffin.