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ALLAN HANCOCK PACIFIC EXPEDITIONS 



VOL. 2 



23. Tergestia laticollis 



Caranx caballus 



Auxis t hazard 

 Gymnosarda alletterata 

 G. pelamis 



Mediterranean 



These 23 species constitute approximately 28% of the total number 

 collected. However, 9 of them have a wide distribution, and their occur- 

 rence in both the Atlantic and Pacific may have no particular significance. 

 Such species are: Bucephalus various, Derogenes various, Dinurus bar- 

 batus, D. longisinus, Helicometra fasciata, Hirudinella clavata, Para- 

 hemiurus merus, Sterrhurus fusiformis, Tergestia laticollis. In most of 

 these cases either the fish host is widely distributed or the trematode is 

 highly cosmopolitan in its variety of hosts. Parahemiurus merus is known 

 (to date) only from both coasts of America and from Japan. 



The remaining 14 species (about 17% of the total), marked with an 

 asterisk (*) in the table, are endemic amphi-American species known (to 

 date) only from the tropical regions of the two oceans. A comparison of 

 the Pacific and Atlantic hosts of these species is of some interest. In no 

 case are the hosts the same in the two oceans. In practically every case 

 (two exceptions) the hosts of any particular trematode species in the two 

 oceans are closely related (either closely related genera or species in the 

 same genus). In other words, the parasite is apparently identical in the 

 two oceans, but the hosts are not identical, although almost always closely 

 related. Or, one can say the parasites are even more similar than are the 

 hosts. The two exceptions are Helicometrina nimia, which shows little 

 specificity at Tortugas, and Lecithochirimn microstomum, which shows 

 little specificity in the Pacific. The report of Stephanostomum casum from 

 Japan is probably erroneous, although this species might extend into the 

 North Pacific where it has been reported. The presence of Haplosplanch- 

 nus acutus in Kyphosus elegans might be a third exception, but, if the 

 record is correct, the host is probably an accidental one. 



A point of some interest is the fact that none of the trematode genera 

 involved is endemic amphi-American. On the contrary, all these genera 



