A Mussel living in the Branchiæ of a Crab

Abstract

LATE this autumn, while searching for Crustacea at Amroth, in South Wales, I found rather an exceptionally good specimen of the common shore crab (Carcinus manas), which I took back to the hotel to clean and preserve. On removing the carapace, I found a mussel living among the branchiæ, and fastened to them by means of its byssus. It was in good condition, and measured 3/8 of an inch in length. The carapace of the crab measured 21/2 inches wide by 17/8 inches long. I could find no signs on the exterior of the crab of anything remarkable within, nor was there any damage to the shell, or hole through which the mussel could have passed. It seems that the mussel, while yet minute, or in a larval condition, must have been carried into the branchiæ, along the ordinary passages, by the flow of water the crab urges through them; it must there have become entangled in the feathery branches, and lived in this unwonted habitat long enough to have grown to its present size, having its food carried to it by the same water that served to oxygenate the lungs of its host.