PLANKTON OF THE GULF OF MAINE 107 



Equally voracious, and far more destructive to smaller animals in the Gulf of 

 Maine because of its greater abundance there, is the pelagic amphipod Euthemisto. 

 The few Euthemisto stomachs which I have examined all contained copepods, often 

 so nearly intact as to show that they had been swallowed whole and were not torn to 

 pieces by their captor's mandibles. In seven Euthemisto upwards of 20 millimeters 

 long, from several localities (stations 10294, 10296, and 10307), the stomachs were 

 packed with copepods (mostly Calanus, but occasionally Temora) , with more or less 

 other crustacean debris, parts of legs, antennae, etc., and in one instance a fish egg. 

 The presence of an entire young Euthemisto in the stomach of one adult shows that 

 this amphipod, like so many other marine animals, is cannibalistic when opportunity 

 offers. Euthemisto is so large and so active that wherever it is abundant it must 

 wreak havoc among the Calanus hordes among which it swims. Probably it 

 materially decimates the stock of copepods existing all along the outer edge of the 

 continental shelf (p. 165), and it may also be a serious enemy to them locally and 

 temporarily within the gulf. Small individuals of Euthemisto feed on unicellular 

 organisms as well as on Crustacea, specimens about 10 millimeters long 51 from the 

 western basin, August 31, 1915 (station 10307), containing more radiolarians (Acan- 

 thometron) than copepods. 



Decapod larvae, so abundant at times in shallows and in coastwise waters, are also, 

 as a rule, carnivorous in their later stages (vide Steuer's (1910, p. 631) account of 

 zoeas devouring young fish, smaller Crustacea, etc.). Lobster larvae also feed 

 greedily on other young decapods of smaller size (Weldon and Fowler 1890), their 

 cannibalistic habit being the bane of the fish-culturist. Lebour (1922), however, 

 describes crab zoeas as also eating green plant cells, Phaeocystis, and diatoms, most 

 often Coscinodiscus among the latter. The young lobster also consumes diatoms 

 in large amount, likewise fragments of algae during its pelagic life (Herrick, 1S96), 

 and this is probably true of most other decapods, if not of all Crustacean larvae 

 at least when they are newly hatched and until they are large enough to capture and 

 subdue more active organisms. 



Sagittae are strictly carnivorous and so active, fierce, and well-armed that it is no 

 wonder they are recorded as feeding on things as far apart as tintinnids, crustaceans, 

 other Sagittae, and young fish. Among the Gulf of Maine species, 5. maxima is 

 notable in this respect, for while the commoner S. elegans and EulcroTinia hamata are 

 usually empty or contain, at most, oil globules or unrecognizable debris, I have on 

 several occasions found S. maxima that had perished in the preservative while in the 

 act of devouring animals as large as Euchaeta and Tomopteris, as well as their own 

 kind, or containing in their guts newly-swallowed copepods or smaller Sagittae of other 

 species. Lebour (1922 and 1923) speaks of the larval herring as frequently falling 

 victim to Sagittae, which may be serious enemies when as plentiful as they often are 

 in the Gulf of Maine. 



It is probable that the comparative scarcity of copepods, often remarked 

 at the precise levels, localities, or times when Sagittae abound, is direct evidence 

 of the extent to which the latter may reduce the stock of their prey. But of all the 

 members of the plankton, the most destructive to smaller or weaker animals are the 



" Euthemisto as small as this can contain but one or two large copepods at the most. 



