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.

Stenorhynchus seticornisOnce 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.

14 comments:

  1. What an experience. What beautiful things tou can see under water! Thank you. I didn't know that species.

    ReplyDelete
  2. Beautiful image and subject, very nicely done !!

    ReplyDelete
  3. @ Antigoni - Thank you! I'm glad you were able to see something completely new to you here on The Right Blue.

    @ Bernie - Thank you very much.

    Bobbie

    ReplyDelete
  4. What an interesting little creature. Love the shot of it and I'm so glad you included those purple claws. Thanks for the info on them too. :-)

    ReplyDelete
  5. Very cool. I can say I learned something today. Thanks
    Cheers

    ReplyDelete
  6. @ Ankush - Thank you so much.

    @ 2Sweet - I just love those little purple claws. Glad you liked them, too.

    @ Fish Whisperer - Thank you. I'm always pleased to know that a reader learned something new from The Right Blue.

    Bobbie

    ReplyDelete
  7. What a strange creature. His shape and movement is so alien.

    ReplyDelete
  8. Hi ScienceGuy - Most of the crabs in this family (Majidae) are a little odd looking, morphologically. Quite a few in the family look "spidery" and have pointy heads to one extent or another.

    Bobbie

    ReplyDelete
  9. He does have an odd-shaped head. Seems there are many underwater creatures that only come out at night - I never knew that until I visited your blog!

    ReplyDelete
  10. Thanks for pointing out the colourful bits. They show up fine when I click on the picture. It's true, with the flashes of gold and perfect nails, he does bear a striking resemblance to my Aunt Daisy.

    ReplyDelete
  11. @ Kathy - That is true. There are many, many creatures -- especially invertebrates -- that come out onto the reef mainly at night. Conversely, many fish "sleep" at night.

    @ Lavender -- are you implying that your Aunt Daisy is a little crabby?? :-D

    Bobbie

    ReplyDelete
  12. Arrow crabs are one of my favorites. They remind me more of characters found in Science Fiction movies and books (which is probablywhy I like them)

    ReplyDelete
  13. Hi Roy - That's a good description of Arrow Crabs. They are kind of science-fiction-y.

    Bobbie

    ReplyDelete

We welcome your comments and invite your questions. Dialogue is a good thing!

Bobbie & Jerry