The Yellowline Arrow Crab (Stenorhynchus seticornis)

by B. N. Sullivan

One of my favorite macro photography subjects on Caribbean reefs is the Yellowline Arrow Crab (Stenorhynchus seticornis). At first glance, these creatures resemble pointy-headed, long-legged spiders. The way they skitter around on those long legs also lends to that first impression.

Once you see a good macro photo of the Arrow Crab, however, you will notice some features that you would never see on a spider. First there is that elongated pointy head, with the goofy eyes protruding on either side. Next you will notice that their legs are jointed, and their 'knees' are a bright yellow color. At the end of each of their forelegs is a little claw. The claws are violet, making them look as if they've just come from the nail salon.

Yellowline Arrow Crabs are abundant throughout the Caribbean, but they are very small, and they are sometimes hard to spot during the day. They tend to find resting spots in nooks and crannies where they stay put during daylight hours. They actively forage at night, so they are quite easy to find on night dives when they are roaming around the reef looking for a meal. By the way, they are carnivores, but you don't have to worry about getting chomped by an Arrow Crab. They eat tiny worms and other itty-bitty animals that populate coral reefs.

They don't seem to be afraid of divers -- even divers with bright lights and cameras -- so once you locate an Arrow Crab, it is fairly easy to photograph it. They don't spook when the camera strobes flash, so the photographer usually will have plenty of time to take a number of shots of a given individual.

I photographed the Yellowline Arrow Crab on this page during a night dive at Little Cayman. This is a 1:2 macro shot. The creature is only about two inches (5 cm) long.