TREMATODES FROM FISHES — ^LINTON 25 



Order DIGENEA van Beneden. 1858 

 Suborder Gasterostomata Odhner, 1905 



Family GASTEROSTOMIDAE Braun, 1883 



Subfamily Gasterostominae Monticelli, 1892 



Genus GASTEROSTOMUM Siebold, 1848 



GASTEROSTOMUM ARCUATUM Linton 



Plate IS, Figures 234. 235 



Oasterostomtim arcuatum IjINTon, Bull. U. S. Fish Comm. for 1899, pp. 277, 278, 

 297, 298, figs. 85-90, 1900 ; ibid., p. 446, 1901 ; Bull. U. S. Bur. Fish., vol. 24, 

 pp. 363, 365, fig. 235, 1905. 



As in other species of the Gasterostomidae, -when any considerable 

 number of individuals are examined, much variation in the relative 

 positions of the genitalia is seen. This is due, in large part, to the 

 ova, which often accumulate in enormous numbers. Thus, in the 

 specimen figured it will be noted that the cirrus pouch extends only 

 about halfway from the posterior end to the second testis, whereas 

 it was represented in the original description of the species as ex- 

 tending to the second testis. Also, instead of only about three vitel- 

 line follicles on each side behind the level of the ventral sucker, there 

 are in this specimen about twice that number. The number of 

 follicles is, as a rule, 16 on each side. In the specimen figured the 

 number appeared to be 16 on the left side and 15 on the right. The 

 saccular intestine, in uncompressed specimens, seems to extend back 

 to the ventral sucker, but in flattened specimens it may extend both 

 anteriorly and posteriorly, as shown in the figure. 



Measurements in balsam: Length, 2.38 mm., breadth, 0.28 mm.; 

 anterior sucker, length, 0.075 mm., breadth, 0.081 mm. ; ventral sucker, 

 length, 0.06 mm., breadth, 0.066 mm.; ova, rather thick-shelled, about 

 0.018 by 0.01 mm. 



Hosts. — This species appears to be of frequent occurrence in the 

 bonito {Sarda sarda), where it has been found free in the stomach 

 and intestine, also encysted in the pyloric caeca and liver. Other hosts : 

 Common mackerel {Sco7nher scotnhrus) ^ cutlassfish {Trichiurus leptu- 

 ncs), common codfish {Gadus morrhua). 



Record of collections. — Recorded from the bonito on 19 dates in 

 July and August, in 9 different years, from 1903 to 1928; approxi- 

 mately 1,100 from 15 fishes in July and 500 from 15 fishes in August 

 (U.S.N.M. No. 8170). 



