as to crabs, I'll refer to my own paper (And references therein):
Plotnick, R. 1985, Lift-based mechanisms for swimming in eurypterids and
portunid crabs.
Trans. Royal Society Edinburgh,
76:325-337.
(copies available on request off-list)
Some portunids use a sculling motion on one appendage see: Kuhl, H. 1933.
cited in my paper.
-Roy
Roy E. Plotnick
Professor
Department of Earth and Environmental Sciences
University of Illinois at Chicago
845 W. Taylor St.
Chicago, IL 60607
plotnick@uic.edu
office phone: 312-996-2111 fax:
312-413-2279
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web page:
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"The scientific celebrities, forgetting their molluscs and
glacial periods, gossiped about art, while devoting themselves to
oysters and ices with characteristic energy.." -Little Women,
Louisa May Alcott