Muscle receptor organs in some decapod crustacea

The presence of muscle receptor organs was determined in the abdomen of ten species of decapod Crustacea. These were Pandalus danae, Paracrangon echinata, Crago franciscorum, Eualus sp. (tribe Caridea) belonging to the Natantia, and Munida quadrispina (tribe Galatheidea), Upogebia pugettensis, Callianassa gigas (tribe Thalassinidea), Paragus aleuticus, P. alaskensis, P. kennerlyi (tribe Paguridea) belonging to the Reptantia. Responses of the sensory neurons were obtained by flexion of the joints of isolated abdomens, and in some cases by stretching the organs themselves or by the use of acetylcholine. All species yielded slowly-adapting responses and some gave also fast-adapting responses. Anatomical examination was used to confirm the existence of the organs in a number of species. In one species of true crab, Cancer magister (tribe Brachygnatha), no evidence was obtained, either physiologically or anatomically, for the presence of muscle receptor organs. The known distribution of muscle receptor organs in higher Crustacea is tabulated and the possible widespread occurrence of such organs in the Crustacea as a whole is discussed.