A fisherman collected this crayfish in Schoharie Creek, near Delanson, New York and took this quick picture before using this as bait. Here’s his reaction, recorded with his phone:
Being a neuro guy, I wondered if the extra segments have muscle and neurons, or whether they were just “blank” exoskeleton. The word I received was that the extra claw was not moving.
The picture and video made its way to a colleague, Frank Dirrigl, and eventually to me. I have never seen a deformity like on this crayfish before. Anyone ever seen anything like this before? Leave word in the comments!
Additional, 18 July 2013: This deformity is unusual, but not rare. You can get these sorts of outgrowths fairly easily following injury. In particular, Nakatani and colleagues (1998) show pictures that are very reminiscent of the one above. Thanks to Joe Staton, Marina Araújo, and Gerhard Scholtz for these references:
References
Araújo M, dos Santos TC. 2012. New record of malformation in the true crab Ucides cordatus (Linnaeus, 1763) (Crustacea, Decapoda, Ucididae), at Brazilian coast. Revista Nordestina de Zoologia, Recife 6(1): 15-19.
Mantellatto FLM, O'Brien JJ, Alvare F. 2000. The first record of external abnormalities on abdomens of Callinectes ornatus (Portunidae) from Ubatuba Bay, Brazil. Nauplius 8(1): 9-97.
Nakatani, I., Oshida, Y., Kitahara, T. 1998. Induction of extra claws on the chelipeds of a crayfish, Procambarus clarkii. The Biological Bulletin 195: 52-59.
Przibram, H. 1921. Die Bruchdreifachbildung im Tierreich. Wilhelm Roux Archiv für Entwicklungsmechanik der Organismen 48: 205-444.
Shelton, P.M.J., Truby, P.R., Shelton, R.G.J. 1981. Naturally occurring abnormalities (Bruchdreifachbildungen) in the chelae of three species of Crustacea (Decapoda) and a possible explanation. Journal of Embryology and Experimental Morphology 63: 285-304.
Pinheiro MAA , de Toledo TR. 2010. Malformation in the crab Ucides cordatus (Linnaeus, 1763)(Crustacea, Brachyura, Ocypodidae), in São Vicente (SP), Brazil. Revista CEPSUL - Biodiversidade e Conservação Marinha 1(1): 61-65.
Crossposted at NeuroDojo.
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