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Featured Shellfish - Floatsam Crab

 Featured Shellfish April 2010

Flotsam crab - Planes spp.

The rare pelagic crab

In Oregon, there are not many crabs living anywhere but the bottom of the sea or estuary. Flotsam crabs are the exception.

Two species are found in Oregon: Planes major (formerly P. cyaneus) and Planes marinus. Both species is known for living on floating debris (flotsam), derelict fishing gear, and even upon live animals (e.g. sea turtles).

When found it is often by those looking for glass floats, which these crab often live on, needless to say, Planes crab are a rare find.

Planes major
Planes major

ID Photo

aka. Columbus crab - Planes spp.

The species Planes marinus is by far rarer of the two species found in the Pacific Northwest (G. Jensen, pers comm.) This genus of crab is also referred to as "Columbus crabs"

Columbus and his crew, during their journey to the new world “saw much more weed appearing, like herbs from rivers, in which they found a live crab, which the Admiral kept. He says these crabs are certain signs of land…” (Markham, 1893)

The weeds were most likely Sargassum, a pelagic (often offshore) seaweed.

The crabs described are likely the Planes species crab, thus thereafter this genus is often referred to as “Columbus crabs” (Chance, 1951)

Planes marinus
Planes marinus
Planes marinus

ID Photo

We all have less sea-fairing relatives:

Ironically, other grapsid crabs found in Oregon are our most land oriented. Almost exclusively found above the low tide line and often above the high tide line. Planes species are grapsid crabs, as such, very closely related to Lined shore crab, Pachygrapsus crassipes, (right).

Also closely related, are two other shore crabs, Yellow shore crab, Hemigrapsus oregonensis, and Purple shore crabs, Hemigrapsus nudus, and the feared Chinese mitten crab, Eriocheir sinensis (To date not found in Oregon).

pachygrapsus
Lined shore crab, Pachygrapsus crassipes
pachygrapsus

 

References:

Chace, F.A. 1951. The oceanic crabs of the genera Planes and Pachygrapsus. Proceedings of the United States National Museum 101: 65–103.

Jensen, Greg. University of Washington

Markham, C. R. 1893. The journal of Christopher Columbus (during his first voyage, 1492-93), and documents relating to the voyages of John Cabot and Gaspar Corte Real, liv-f 240 pp. Hakluyt Society, London

Acknowledgements:

Many thanks to Harry Allen, F/V Shenanagen for bringing fun stuff into the office and Dr. Greg Jensen for his vast knowledge of marine fauna and willingness the share it.



 

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