“Without a doubt what moves my soul is nature.” - Observation of the Week, 9/4/18

Our Observation of the Week is this Allopetrolisthes spinifrons porcelain crab, seen in Chile by @marceloandrsrojasgonzlez!

“One day in a biology book I saw a picture of the Porcelain Crab (Allopetrolisthes spinifrons) and it was like love at first sight, so I started looking for it,” explains Marcelo Andrés Rojas González. “Reading a bit, I knew that it only lived on some types of anemones, and it searched for over one year until I found it; it was a day of maximum happiness.” He has since returned to the area and has watched the crab and its anemone grow over time.

True to their common name, Porcelain crabs (Family Porcellanidae) “break” easily when agitated or threatened, shedding their limbs to escape capture. However, they are not “true” crabs (Infraorder Brachyura) but related to squat lobsters and represent the phenomenon of “carcinisation”, in which non-crab organisms evolve to have crab-like body shapes. Look carefully and you’ll notice that Porcelain crabs only have three pairs of legs for walking (rather than the four pairs of true crabs), and their long abdomens usually tucked under their bodies. Allopetrolisthes spinifrons, however, exhibits “hypercarcinisation,” as their abdomens are analogous to the sexually dimorphic pleons of true crabs.

Most Porcelain crabs reside under rocks and other cover, but as Marcelo noted this species of Porcelain crab lives on anemones. They use the anemones not only for protection - stinging tentacles and all that - but staying on the anemone allows these filter feeding crustaceans access to higher quality food matter  than that found under rocks. They also nosh on anemone feces and mucus. The crabs’ large pincers, like those of other Porcelain crabs, are used for territorial disputes and protection, not for feeding.

Becoming an underwater photographer “has not been easy,” says Marcelo (above), “the equipment is expensive and to be able to do underwater photography you have to have highly developed diver skills; do not forget that breathing underwater is not natural for us.” For the the past two years, he has used his photographs in desktop calendars has a new one planned for 2019. He says iNaturalist not only provides another avenue for him to share his photos with others, it also helps him learn taxonomy and identify his findings.

“In all this time I have had to learn from a new world,” he muses. “I have no formal studies of biology, so everything was new for me...I am a civil engineer, but without a doubt what moves my soul is nature.”

- by Tony Iwane. Some quotes have been edited for clarity.


- Watch a Porcelain crab use its maxillipeds to feed, and... 

- ...read a paper detailing the feeding techniques and behavior of Allopetrolisthes spinifrons.

- Check out our blog post about iNaturalist in Chile from last year.

Posted by tiwane tiwane, September 05, 2018 05:59

Comments

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Impressive, such crab exist. Does it mean their life is vulnerable.

Posted by astlab over 2 years ago (Flag)
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Just a gorgeous photo of a crab that very few of us will ever see. Thank you for being part of the iNaturalist community. Live long and dive often!
Pam (moabgardener)

Posted by pam-piombino over 2 years ago (Flag)
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Absolutely gorgeous! Thanks for all your efforts -- they are much appreciated.

Posted by susanhewitt over 2 years ago (Flag)
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I agree -- this is a great observation and an equally great naturalist! Great job! :)

Posted by sambiology over 2 years ago (Flag)
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Beyond words, really; one can truly sense the depth of your love of nature, mary137

Posted by mary137 over 2 years ago (Flag)

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