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Pea crabs symbiotic with polychaetes

Jack Pearce buzbay at cape.com
Fri Nov 30 16:32:41 EST 2001


I have worked with the "pea crabs" since 1957 when I begain my grad 
career at the Friday Harbor Labs, U. of Wash. I worked most with the 
bivalve parasite spp but collected numerous forms that are symbiotic with 
polychaetes, and some other vermiform taxa. I had postdocs in Denmark 
and Scotland and was able to collect in most European waters. Several 
things are  important: the likes of Fabia (really should be Pinnotheres) 
and Pinnotheres should be in a separate family relative to the pinnixids, 
which have completely different life histories. I spoke several times with 
Waldo Schmidtt about this issue before he died.  

The several species of Pinnotheres (and Fabia and others) have two 
distinct crab instars which are free-living, usually in the water column 
(this is described in my paper in Pacific Science). The pinnixids don't 
carry-on this way and the males and females live together in bivalve (and 
I suspect polychaete) hosts. In Pinnotheres, the males and females 
copulate in the open water, with the female (fully inseminated) returning 
to the host spp to complete the series of instars leading to the so-called 
Stage V ovigerous form. All this in spite of whart Christensen and 
McDermott said earlier about the males seeking out females in the host 
bivalves of the latter!   

Pinnixa faba and littoralis always interested me in as much as that they 
seemed to violate Gause's hypothesis about two spp NOT occupying the 
same niche'. I suspect that P. eburna, schmitti, and others are equally 
interesting in how they share their several vermiform hosts.  

I would be glad to correspond with you in these regards; Mary Petersen, 
the Copenhagen Museum might also be a font of knowledge as she 
worked widely with worms in the U.S. southeast and is a great observer!  

Best of luck and keep in touch. I have worked with several species with 
re: to DNA (with colleagues at MBL) to see if any cryptic spp are involved 
where one sp, P. maculatus, occupies two or more host spp.  

Cheers, Jack Pearce, North American Editor, Marine Pollution Bulletin
             Buzzards Bay Lab., 54 Upland Av., Falmouth MA 02540   USA
             buzbay at cape.com,   508-540-4572,   fax 508-457-0105

Greg Farley wrote:

> [apologies for crossposts!]
> Dear colleagues:
> Hello!  By way of introduction, I am a graduate student at Florida State
> University in Tallahassee.  My research revolves around the evolution and
> ecology of commensalism, and I'm using pea crabs (Brachyura:
> Pinnotheridae) as a model system. 

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