56 M. R. CARRIKER, D. B. SCOTT, AND G. N. MARTIN, JR. 



biates mechanical devices such as valve edges in pelecypods, 

 radulae in gastropods, and bristles in polychaete and sipunculid 

 worms and in barnacles mav be emploved alone in penetration of 

 relatively soft materials; but perforation of hard exoskeletons prob- 

 ably requires chemomechanical means (Carriker, 1961). 



Since 1941 the senior author has been studying the biology of the 

 demineralization-boring mechanism of drilling gastropods in an at- 

 tempt to gain a better understanding of the mechanism in these 

 snails, and to provide a basis for a wider comparative studv of simi- 

 lar mechanisms in other mollusks and in other in\ ertebrates (Car- 

 riker, 1943). Recent species of gastropods which bore are all 

 predatory, feeding on the bodies of animals enclosed within shells, 

 and are known to exist mainlv in the Families Muricidae ( including 

 Thaididae) and Naticidae, Subclass Prosobranchia; continued ex- 

 ploration may well disclose them in other gastropod families. 



As currently understood, drilling in muricid and naticid snails con- 

 sists of a chemical phase in which an accessory boring organ, ABO 

 ( demineralization gland), secretes a neutral substance which acts 

 on the shell at the site of penetration, and a mechanical phase in 

 which the radula rasps off the weakened shell as minute flakes which 

 are swallowed (Carriker, 1961). Descriptions of various aspects of 

 the anatomy, histology, and function of the organs involved in bor- 

 ing in muricids are given by Carriker ( 1943, 1955, 1957, 1959, 1961), 

 Fretter (1941, 1946), and Graham (1941); in naticids by Ankel 

 (1937, 1938), Boettger (1930), Fischer (1922), Giglioh ^( 1952), 

 Gunter (1936), Hirsch (1915), Schiemenz (1891), Turner (1953), 

 and Ziegelmeier ( 1954 ) ; and in both families in a review in an im- 

 pressive new volume by Fretter and Graham (1962). Many aspects 

 of this biology are still grossly incomplete. 



In muricids the ABO, withdrawn within a sac in the mid-anterior 

 part of the sole of the foot, is everted only in operation; in naticids 

 it lies under the distal tip of the proboscis. The ABO takes the form 

 of a papilla, mushroom-shaped in muricids and pad-shaped in nati- 

 cids, and has a distal cap of a very tall distinctive secretory epithe- 

 lium, strikingly different from other epithelia in the snail body. The 

 diameter of the ABO slightly exceeds that of the tip of the proboscis, 

 and approximates the diameter of the bore hole made by it. 



