1) scolex type described by Yamaguti (1959) was 

 retained. 



Fistulicola plicatus specimens recovered from the 

 lumen of the intestines were morphologically dif- 

 ferent from those collected from the rectum. They 

 were long, up to 1 m in length, and exhibited longer, 

 less-broad strobila than those characteristic of the 

 rectal forms. All specimens of F. plicatus recovered 

 from the anterior portion of the intestine exhibited 

 the previously described first type of scolex attach- 

 ment to the organ wall, i.e., the scolex perforated 

 the organ wall and was encapsulated in a rounded, 

 host-produced cyst attached to the intestinal serosa. 

 The scolex penetrated the anterior portion of the 

 intestine, with the strobila projecting posterior 

 through the length of the organ. Very small F. 

 plicatus were found in the posterior portion of the 

 intestine. These exhibited shallow penetration by an 

 unmodified scolex. 



Fistulicola plicatus specimens found in the rec- 

 tum of swordfish were usually <20 cm in length and 

 possessed very broad strobila. These rectal forms 

 exhibited all of the previously described types of 

 scolex attachment and structure, penetrating the 

 organ wall near the rectal sphincter (Fig. 5). Occa- 



sionally, several tapeworms were found with their 

 necks passing through a single perforation of the 

 rectal wall, their scolices jointly encapsulated in a 

 rounded serosal cyst. 



Discussion 



Apex type predators such as the swordfish eat and 

 digest large amounts of prey species and, conse- 

 quently, the intestines and rectums of these fish 

 exhibit high levels of muscular activity. Without per- 

 foration of the organ wall (by the scolex and neck), 

 many tapeworms would probably be voided with the 

 faeces. The development of the pseudoscolex is an 

 adaptation for anchoring the simple, unarmed scolex 

 to the organ wall. It is clear that F. plicatus secretes 

 a powerful digestive enzyme which enables the 

 scolex to penetrate the very muscular walls of the 

 intestine and rectum of swordfish. lies (1970) found 

 many examples of pseudoscolex variation in 24 

 specimens from swordfish in the Northwest Atlan- 

 tic Ocean. Several of these variations are similar to 

 those found in this study. It is obvious from this 

 study, and studies such as lies (1970), that F. 

 plicatus is a very adaptable tapeworm and will 

 develop any pseudoscolex structure which is neces- 



Figure 5. —Fistulicola plicatus (in situ) from rectum of Xiphias gladius. 



756 



