Phronima, a creepy amphipod

Description: Phronima spp. is a hyperiid amphipod that normally lives in deep water. It also normally lives inside a "barrel" formed from the body of a salp or related creature. That's right--all the tissue from the salp's inside is carved out, and the remaining husk is used as a floating home and a place to lay eggs.

I found this specimen when I was jellyfishing at the docks of the Friday Harbor Labs (San Juan Is., Washington state) in June 2014. It was swimming at the water surface. The reason I noticed it (it's transparent, after all) was because of its unusual swimming movements. It had no barrel when I found it, and I'm not sure if it was a male or female.

I have so many questions about these guys I hardly know where to start, so I'll just list a few. (Note: I've read a few papers that describe aspects of Phronima natural history, but I haven't really delved into it. Some of this info may already exist for certain species.)

1. How does a Phronima pick out an animal to use as a barrel?

2. Does the size of the amphipod relative to the barrel matter? Do they need to change barrels as they grow larger?

3. How does mating occur? I think the amphipods live one-to-a-barrel (except when the females have babies), so do both the male and the female both have to leave their barrels? Or does one invite the other over to its barrel?

4. If a Phronima leaves its barrel, can it find the same one to go back to later?

5. Could a Phronima be persuaded to live in an artificial barrel? Does it just need something that shape, or is there something special about the tissue itself?

Page creator's name: Yasmin von Dassow; pics/video by Mickey von Dassow; movie by both
Page creator's contact info: Page creator does not wish to be contacted.

biology eyes invertebrates marine vision

Created: 08 Dec 2014 22:39
Updated: 06 Jan 2015 21:37


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