Observation of the Week, 5/20/16

This Phronima sedentaria seen by @nikbaines in New Zealand’s Otago Peninsula is our Observation of the Week.

iNaturalist user Nicola Baines found many little jelly-like organisms washed up on the beach, and several had what she said looked like “mini transparent lobsters” in them. She posted photos of them in iNaturalist “keen to know” what they were, and also uploaded a video to YouTube.

Lisa Bennett (@lisa_bennett), who had studied Antarctic pelagic amphipods, recognized the tiny crustaceans as members of the Phronima genus of amphipods. Most of us are familiar with amphipods as sandhoppers and lawn shrimp, living under rocks and eating detritus, but the amphipod suborder Hyperiidea are planktonic in habit. Many have “relationships with gelatinous zooplankton, such as salps and cnidarians,” says Lisa, which “can vary from obligate parasites to ectocommensals.”

Using its formidable front claws, members of the Phronima genus carve out the insides of salps (free-floating tunicates), jellyfish and siphonophores and use them as buoyancy devices. The salp walls still contain living cells, which may help it maintain its form. Female Phronima will lay their eggs in it “then propel it around like a pram or buggy until the young are ready to be released,” says Lisa.

Nicola’s observation was the first Phronima of any kind posted on iNaturalist - a curious citizen scientist and a knowledgeable community working hand in hand!

- by Tony Iwane

- Phronima are often cited as the inspiration for the creature in Alien, or for the Alien Queen in Aliens, but I couldn’t find any evidence to support this claim. What do you think?

- Really great footage of Phronima in action.

- iNat user @steve_kerr scouted out the beach where Nicola came across her Phronima and he took some fantastic photos of the ones he found!

Posted by tiwane tiwane, May 20, 2016 06:30


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