This red, sausage-sized structure is the external portion of an unusual, parasitic barnacle, Briarosaccus callosus, found on many species of king crabs. Here the barnacle is parasitizing a scarlet king crab, Lithodes couesi, collected on Pratt Seamount. The parasite sterilizes its hosts and uses their energy to produce hundreds of thousands of barnacle larvae, which closely resemble the larvae of the more typical acorn barnacles. One of the many unusual features of the barnacle is its bright red color, caused by hemoglobin. The barnacle also induces its crab host to protect it and also assist with larval release. Image courtesy of Tom Shirley
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