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, antennte, 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 larvse, 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, Phseocystis, 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, 1896), 
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. 
Sagittse 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 Sagittse, and young fish. Among the Gulf of Maine species, S. maxima is 
notable in this respect, for while the commoner S. elegans and Eukrohnia 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 Sagittse of other 
species. Lebour (1922 and 1923) speaks of the larval herring as frequently falling 
victim to Sagittse, 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 Sagittse 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 
51 Euthemisto as small as this can contain but one or two large copepods at the most. 
