GULF OF MEXICO 



343 



any of five other species of fishes belonging in 

 five otiier families. 



If a trematodo species occurs in 2 or several 

 hosts, the hosts are usually related. For example, 

 138 trematodo species (73 percent of those col- 

 lected) were limited to a single host genus. Only 

 rarely is a trematode species found in fishes be- 

 longing in different families. Little is known 

 regarding the host specificity of larval stages for 

 their intermediate hosts. It is sometimes greater, 

 particularly for the molluscan host, than that of 

 the adult parasite. 



This tendency of trematodes to occur in a 

 limited number of hosts which are usually related 

 gives added interest to the geographical dis- 

 tribution of these parasites. During my study of 

 Tortugas trematodes, I was frequently impressed 

 to discover that the hosts of the same or a related 

 trematode in distant oceans proved to be a fish 

 related to the host at Tortugas. 



GEOGRAPHICAL DISTRIBUTION OF 

 TREMATODES OF FISHES AT TORTU- 

 GAS, FLORIDA 



TREMATODES FROM 50 FATHOMS OR BELOW 



Systematic dredgings south of Loggerhead Key 

 under the direction of Dr. W. H. Longley in the 

 summers of 1930-32 presented an unusual op- 

 portunity for collection of trematode parasites 

 down to depths of some .500 fathoms (Manter, 

 1934). It was found that fishes down to that 

 depth were as commonly infected as fishes of 

 shallow (surface) waters, 49 species being col- 

 lected from about 90 species of fishes. These 

 trematodes are almost entirely different species 

 from those occurring in the nearby surface water; 

 only 3 species from below 100 fathoms occurred in 

 lesser depths and 2 of these are atypical {Dis- 

 tomum fenestratum is an immature, very non- 

 specific species, while Sterrhurus floridensis has so 

 little host specificity that precocious maturity in a 

 crustacean host is suggested). Even at 50 fathoms 

 only 3 additional species {Deretrema fusillus, 

 Myzoxenus vit-ellosus, and Helicometrina nimia) 

 occur in surface waters at Tortugas. This marked 

 difference in the deeper water fauna might be 

 expected since the fishes and invertebrates are 

 also different species. 



A more interesting aspect of the deeper water 

 trematode fauna is the affinity it shows for distant, 

 cool or cold water faunas. Manter (1934) noted 



a number of species found only at 50 fathoms or 

 below at Tortugas but known from surface waters 

 of the North Atlantic. Studies since 1934 add 2 

 species which do extend into surface waters at 

 Tortugas and some 6 species found in distant 

 oceans. The following table shows the distribu- 

 tion of these species. Numbers in parentheses 

 indicate the number of host species involved. 

 The table is based on a total of 41 adult species 

 definitely identified. 



The above data suggest that a bathymetric 

 barrier between the trematode faunas of surface 

 waters and of depths 100 fathoms or more at 

 Tortugas is more effective than any existing be- 

 tween the deeper fauna and distant cool oceans. 

 The deep-sea fauna itself is evidently very wide- 

 spread, but a number of its trematode species 

 occur in more shallow depths near or in the Arctic 

 and Antarctic Seas. 



The above comparisons have been on the spe- 

 cies level. It is of some further interest to note 

 that of 13 new genera named in 1934 from deep 

 water at Tortugas, 7 involving 15 species have 

 since been reported elsewhere as follows: One (1 

 species) from Woods Hole; four (11 species) from 

 Japan; two (3 species) from Tasmania. The 

 species from Tasmania were in shallow-water 

 fishes. 



