7 Jun 2013

Who am I??? I am a...

It's finally here! The day you've all been waiting for! The answer to my World Oceans Day riddle!!! ;o)

First of all I just wanted to give a big thank you to Kim from Snug Harbour Bay whose holiday photos from Sanibel Island gave me the idea to choose this critter, and her daughter Chablis who kindly sent me a series of photos she took so I could use them in this post! :o)

Let's start by reviewing the clues, which I've enhanced with a few links to useful information. Try and figure it out as we go along, no cheating by jumping to the end! :p

1. I am a LIVING FOSSIL! I am very old. I pre-date flying insects, dinosaurs and man.
2. I am a marine animal, with only four species alive today.

4. I can walk using my five pairs of walking legs. I have an extra pair of cephalothorax appendages which I use to get food to my mouth. These have a special name which I won't share just yet 'cause they might give the whole game away! ;o)
5. I can swim ("upside down"!) using my abdominal plates (fused abdominal appendages)
6. I have a hard dorsal shell called a carapace and a long needle-shaped tailpiece called a telson. In order to grow in size I will have to molt, shed my shell (I come out 25% bigger than before!), several times during my life. After 16 molts (~9-12 years) I will have reached my full adult size.

7. I have two compound lateral eyes and five simple eyes on my carapace.
8. I "breathe" (capture oxygen from the water) using book gills (flat, leaflike gills), present on some of my abdominal appendages.
9. I am a true blue-blood! (You can call me "your highness"!) This is because my blood uses hemocyanin instead of hemoglobin to carry oxygen. The copper present in the hemocyanin makes it blue!

10. I come out at night to eat worms and small molluscs, but hide (usually in the sand) during the day.
11. If I'm a male I'm smaller than the females and my first pair of "legs", the pedipalps, are modified as a grasping appendage so I can hold on to the female during spawning.
12. We (males and females) meet up on the beach during spawning season (May-June). I detect her through the pheromones she releases, and "hold on" to her as she lays the clutches of eggs while I fertilize them.

13. My first pair of appendages, which I use to place food in my mouth, are called chelicerae. They're present in all my relatives, which is why our subphylum is called the Chelicerata.
14. Some people find my shape reminds them of a horseshoe...
15. My name is a misnomer! I am not a crab!!! (but we are distantly related)
Who am I???

Limulus polyphemus. Photo by Chablis Scornavocco, taken at Sanibel Island, Florida, USA.
Source: Wikipedia

Like I said, I am NOT a crab! Although like them I belong to the phylum Arthropoda (same group as crustaceans, insects, centipedes, spiders etc.), I'm a chelicerate, which means I'm closely related to spiders and scorpions!
And guess what? I HAVE MY OWN WEBSITE!!! ;o)

How about we take a look at those different body parts I mentioned in the clues?

Here, check out this angle, it will give you a really good look at those eyes!

Photo by Chablis Scornavocco

Horseshoe crabs have been around for over 400 million years, and were probably one of the first species who ventured out of the oceans to lay their eggs on land in order to protect them from predation by other marine species. So their eggs are safe from marine species... but they're now an important food source for migratory birds! Horseshoe crabs can survive for many hours on land, but if they get stranded and flipped on to their backside then they're vulnerable to predation by seagulls and other birds. So if you're lucky enough to see one on the beach - and it's on its back - just flip it over and let it find its way back into the water! No risk of danger to you, despite its name it's not a crab and doesn't have pincers. Sure, you might get pinched if you stick your finger in its mouth, but then if you do that I'd say you deserve it! And while horseshoe crabs are related to spiders and scorpions, the only way that pointy tail will hurt you is if you manage to stab yourself with it somehow! They use the tail as a rudder to plow through sand and muck, and to help flip themselves over if they get "stuck" on their backside.

There are only four species alive today (from Wikipedia):

What's left behind... L.polyphemus molt. Photo by Chablis Scornavocco, taken at Sanibel Island, Florida, USA

I've never been lucky enough to see one alive (only dead and preserved in my Zoology labs at university), but I'm guessing it's quite a sight because the people who solved the mystery early on were all people who have seen them... I was particularly surprised that my Aunt figured it out (on Facebook) on day 2!!! When I asked her about it she said:
"I'm amazed too because I don't know the names of many ocean dwellers. The descriptive clues matched my childhood memories of these ancient critters on the beach."
I asked my dad if he shared these childhood memories, here's what he said:
"When I was a young lad of pre-teen age, growing up in the Northern Virginia suburbs of Washington, DC, my family used to take two week summer vacations to the beaches of Bethany and Fenwick Island, Delware, just a short drive from the famous boardwalk honkytonks of Ocean City, Maryland.  This part of Delaware was a narrow spit of land separating the Atlantic Ocean to the East from the Chesapeake Bay to the West. In the mornings we would play in the sand dunes and frolic in the frothy ocean waves, body surfing or using stiff, inflatable surf rafts to ride the waves to shore. Later in the afternoons and early evenings, we would explore the bay side of the peninsula, where we would go crabbing and catch bluefin crabs for our dinner, using salt pork to bait them and long handled nets to catch them.
On more than one such occasion, we came across what we imagined to be invaders from another planet, coming ashore from the Chesapeake Bay like dozens of miniature military landing craft, row upon row of them, dome-shaped with a hard shell protecting them and a spiked tail sticking out from under the shell.  These were horseshoe crabs and we kids found them repulsive, our wild imaginations running rampant with all sorts of nightmarish scenarios.  We didn't know the biological significance of these creatures at the time and, in our ignorance, felt threatened by them. Sometimes we would find a stick and turn them over, rendering them immobile and harmless (not that they could have caused any harm in any case, but what did we know). "

Invaders from another planet... they do seem pretty alien, don't they? 

Image from www.ecodelaware.com
Here's a brilliant (and short) video I found on YouTube that lets you get a good look at them as they hit the beach during spawning season. Take a look at all the birds hanging around that same beach waiting to feast on the eggs!!!

You remember I said they have blue blood? Well it turns out that stuff is very valuable for the biomedical/pharmaceutical industry! Why?  Because of the amoebocytes in their blood, which function like our white blood cells by fighting off infection. These amoebocytes can be extracted from their blood and used to make Limulus amebocyte lysate, which is used to test the presence of bacteria in pharmaceutical products. Apparently it's very useful, so it's good thing for these critters that there's a relatively harmless way of collecting the blood! Check out this video below (part of a PBS documentary) which illustrates the process and explains why their blood is so valuable. If you're in the US you can probably watch the whole documentary - Crash: A Tale of Two Species - at the PBS website here (I can't, "not available in my region").

Finally, a video of a horseshoe crab swimming. It's pretty cool to see them moving around upside down like that!

Horseshoe crabs aren't just these cool, alien-looking living fossils. They play a key ecological role in their food web! If their numbers were to decrease significantly, it would have a serious impact on many bird species (some of which are already classified as "threatened") who depend upon their eggs for food. Then there are some species of sea turtles which also feed on adult horseshoe crabs. Like all species whose lives are spent in that delicate space where the ocean meets the shore, their survival is threatened by shoreline development and habitat loss. They've also got to deal with the pressures of harvesting to provide bait for conch and eel fisheries (in the U.S.). And of course there are multiple natural causes of death like beach strandings (just flip'em over!), predation and disease.

Interested in getting involved in horseshoe crab conservation? Plenty of ideas here:

Want more horseshoe crab material? Here are a few things I found online which seem interesting!

This post was put together to celebrate World Oceans Day and to participate in the Oceanic Blog-A-Thon! Go check it out and see what other participants have written. It will be up and running Friday afternoon. (my time, I'm finishing this post up at midnight and I'm sick so I'm going to bed!) And better yet, write something fishy and join in yourself! ;o)

Information sources:
Integrated Principles of Zoology - Hickman, Roberts and Larson.


  1. I SO enjoyed this whole post- Super interesting and informative. I could kick myself for not guessing sooner what the answer was. :-) This would make a great monthly series. Thanks Cris.

    1. lol! I thought you might be kicking yourself when you saw the answer Kim! Glad you enjoyed it!

      A monthly series? *sigh* I'd love to! But time is really tight this year... the Blogs are a bit on the backburner because of all the "real world" stuff! :o(

  2. This was certainly fun, and informative to boot. I'm loving your enthusiasm for World Oceans Day. Also sending you big hugs! :-)

    1. So happy you liked it DJan! You know me, how could I be any less enthusiastic about the Oceans?! ;o)


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