Guest Post: In search of a sand crab

Today's post is by the fantastic and phenomenal Zen Faulkes. Be sure to check out his blog after you read it!

Note; I'm writing this guest post because this week, I'll be a visitor in Christie's current stomping grounds, Hawaii, attending the summer meeting of The Crustacean Society. Christie, meanwhile, is on the mainland. Since we are sort of switching places, we thought it might be fun to switch blogs. So here I am at Observations, and she's promised me a guest post for my blog, NeuroDojo.

Hawaii is famous for its beaches. When most people see a beach, they think of relaxation. Tanning, swimming, bikinis, maybe a little Frisbee or beach volleyball.

When I see a beach, I think of shovelling and sweating.

Doing a doctorate changes you, man.

I developed my somewhat warped relationship with beaches during my graduate work. I worked on the locomotion of beach dwelling sand crabs. People who live by beaches might know some of the species as "water fleas" or "mole crabs," which are usually sand crabs in the genus Emerita.

Most of my work was in the lab, as the animals were pretty hardy and survived well in sea tables, but this did mean we had to occasionally go from Vancouver Island down to California to collect animals.

The good news was that the two main species of sand crabs I worked with were very abundant. But the most opportune time to collect them was at low tide, which somehow always seemed to fall just before daybreak on our collecting trips. My relationship with beaches changed after a couple of those 5:00 am wake-up calls, and not for the better.

During a Ph.D., you make it your goal to become knowledgeable on your subject, so I tried to read up on every paper on the sand crab superfamily I could find. There weren't many, and those that did exist were often taxonomic descriptions in nineteenth century journals and specialty journals. And I discovered some odd species that way. Zygopa, a sand crab with only one eye. Stemonopa, a sand crab with eyestalks longer than its carapace. And Mastigochirus.

I would love to see live Mastigochirus.

These genus is pretty obscure, even for sand crabs, which are a fairly obscure group to begin with, truth be told. There are only two species in the genus. But you won't even find the genus name Mastigochirus listed in a massive taxonomic database. You'll find some places that both Mastigochirus and Mastigopus, but the second name is an out-of-date name for the genus (Boyko & McLaughlin 2010), and isn't valid.

Before this post, you would only find a single drawing of the genus on Google Images, which I think is M. gracilas. Today, I'm proud to double that number by including a scan of an Australian species, M. quadrilobatus (from Haig 1974). But there are no photographs, and none of a live one. And the last couple of days, I thought, "Hey, that could be my lame claim to fame: to be the first person to photograph Mastigochirus and put it on the web!" (Go on, say it: "Nerd.")

It's a reminder, though, that not everything is on the web.

Why am I eager to see this genus and not the other extraordinary ones I mentioned?

It's those long legs. Yes, thanks to my doctoral work, I'm a leg man. (As I said: grad school changes you, man). Sand crabs use their legs for digging and swimming in very complicated ways, particularly in this family. In Emerita, the first pair of legs are flattened and paddle shaped, and they use them like rudders to steer when they swim. I look at those long legs in Mastigochirus, and am intensely curious to see how they are used. They don't seem to be great for swimming. They seem almost comical to think of them providing much help in digging. What are they used for?

Simple-minded questions abound when you study sand crabs. For most species (except Emerita), we have essentially no idea of the basic biology of the species beyond the descriptions of their bodies needed for a species description. What does Mastigochirus eat? The other two sand crabs in its family have very different feeding habits: Emerita is a mild-mannered filter feeder. Hippa will come come out of the sand and swim to bait.

I got thinking about all of this because I thought Mastigochirus might live in Hawaii. But re-reading Haig (1974), she described both species living in the Indo-West Pacific. I think I was confusing its distribution with another sand crab genus, Hippa, which definitely does live in Hawaii.

I don't know if I'll get a chance to see any sand crabs while I'm in Hawaii. A scientific conference is work, even when in a lovely place like Hawaii. But if you see guy on Waikiki beach with a shovel and no interest in working on a tan, kicking over and staring intently at the sand, come by and say hi.

References

Boyko CB, McLaughlin PA. 2010. Annotated checklist of anomuran decapod crustaceans of the world (exclusive of the Kiwaoidea and families Chirostylidae and Galatheidae of the Galatheoidea) Part IV-Hippoidea. The Raffles Bulletin Of Zoology Supplement No. 23: 139-151. http://arthroinfo.org/pdfs/31608/31608.pdf

Haig J. 1974. A review of the Australian crabs of the family Hippidae (Crustacea, Decapoda, Anomura). Memoirs of the Queensland Museum 71: 175-189.