Observation of the Week 2016-06-29

This Sea Urchin Crab, seen in Hawaii by davidr, is our Observation of the Week.

“Truth be told,” says David Rolla, “I was uncertain that anyone else would appreciate [this crab] -  after all, in the words of my dive buddy, ‘it’s a butt crab!’”

Yes, the tiny crab you see above, whose scientific name is Echinoecus pentagonus, is ensconced in the anal pore of a sea urchin, and its carapace measures only 1.3 cm (0.5 in) across at most. Ranging from the Red Sea into Polynesia, this crab species is a sea urchin parasite and in Hawaii is found in the rectums of Banded Sea Urchins (Echinothrix calamaris). David has attempted to photograph these tiny crabs before, but “for obvious reasons, capturing a well-lit and properly focused image of this particular crab is rather challenging.” However, on a recent dive off of Pupukea, Oahu, he came across this urchin. “Normally, I would pass by without so much as a glance, but something caught my eye. Upon closer inspection, I could see the crab in its usual location — the anal pore of the urchin.  And on this occasion, the pore appeared to be fully dilated, providing a better view of the crab.” David took a dozen shots of it, and “later that day, when I first saw the image on my computer screen, there was a little rush of excitement — success!!  It is a unique portrait of a rather unusual animal.”

The ocean off of Hawaii is a far cry from David’s childhood in a rural area of the Appalachian Mountains of eastern North America, but his second grade teacher Mrs. Keith maintained a small saltwater aquarium in her classroom that lit a fire in him. “With great interest and enthusiasm, I learned all about the animals and the delicate environment required to support life - the water temperature, salt content, and pH levels,” says David. “In between grammar and arithmetic lessons, we were observing sea stars and breeding seahorses...how cool is that?” Mrs. Keith’s aquarium and his childhood memories of watching The Undersea World of Jacques Cousteau still in his mind, David finally got his SCUBA certification two decades later and has been hooked ever since.

In 2011, NOAA scientist Kyle Van Houtan saw David’s photo of a Hawksbill Sea Turtle (above) and invited him to add it to the Hawaii Sea Turtle Monitoring project on iNaturalist. “To say that [iNaturalist] has changed the way I relate to nature and the natural world would be an understatement,” says David. “It has rekindled my childhood curiosity and passion for learning about all living things. It inspires me to explore, to discover, and to appreciate the mystery and beauty of nature — every day.” He continues to be amazed by the growth of iNaturalist’s community and has enjoyed meeting fellow naturalists both virtually and in person. “Mahalo and aloha to the entire iNaturalist community — especially to those working so tirelessly behind the scenes to make it happen!!”

- by Tony Iwane


- Check out David’s photography on Flickr!

- The bizarre world of parasitic crustaceans - yikes!

- Here’s a video of a slightly different crab-urchin relationship.

- If you want to kick it old school, looks like there are still some episodes of The Undersea World of Jacques Cousteau on YouTube.

Posted by hannahsun99 hannahsun99, August 01, 2020 02:13

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