Foreign Substances Attached to Crabs

Abstract

IN your issue of December 26, 1889 (p. 176), Mr. Pascoe drew attention to the cases of certain crabs which are frequently found covered with sponges, algæ, shells, &c., and brought forward also the well-known case of the Gastropod Phorus. He at the same time confessed that he could not see “where protection came in” in any of the cases which he cited. Mr. A. O. Walker, on the other hand (NATURE, January 30, p. 296), regards it as obvious that the attachment of these foreign substances is a useful adaptation for purposes of concealment. Prof. Herdman also (NATURE, February 13, p. 344) bears witness to the “scarcely recognizable” appearance of the crab Hyas when covered with algæ, &c. Indeed, no one who has seen one of these crabs brought up with the dredge, or has found a well-covered Stenorhynchus on our own shores, can seriously doubt the usefulness of the habit in rendering the animal inconspicuous. In Stenorhynchus and Inachus the process of “dressing” with weeds and zoophytes has been described by Bateson (Journ. Mar. Biol. Association, vol. i. 1889, p. 213), and it is seen from his description that, as also in the cases of Dorippe, Pagurus, Dromia vulgaris, &c., the foreign substances or animals become attached to the body not by accident but by the act of the crabs themselves.