PLANKTON OF THE GULF OF MAINE 333 



Thanks to the confinement of Eukrohnia to considerable depths, where seasonal 

 variations in the physical state of the water are slight, it is easy to establish the 

 temperatures and salinities in which it most often occurs in the gulf, the former 

 ranging from 1.3° to upward of 9°, the latter upward of 32.16 per mille, with most 

 of the Eukrohnia living in water more saline than 32.5 per mille. Assuming 

 Eukrohnia to occur close to the bottom, the maximum salinity in the gulf would be 

 about 34.8 per mille. 



Our largest summer catches of this worm have been made in water of about 

 6 to 8° temperature and of 33 to 34 per mille salinity, with an extreme range from 

 about 5.9° to about 9.3° temperature and from about 32.6 per mille to about 35 

 per mille salinity. In spring we have taken it in 1.3 to 6.7°. The seasonal data 

 thus show that Eukrohnia can survive in the gulf through a considerable range 

 of temperature, from the coldest up to 9° or so, or even slightly warmer, and in 

 water varying in salinity from slightly more than 32 to 35 per mille; that is, in all 

 but the warmest and least saline locations. This is interesting,, for with both the 

 salinity and the temperature of the surface waters within these limits over most of 

 the gulf in winter and spring, and with the water as cool and as saline as this only 

 a few meters down even in midsummer, neither temperature nor salinit}" but probably 

 light is the factor that bars Eukrohnia from the upper layers of water at all seasons. 



With Eukrohnia occurring in the gulf only as an immigrant and not as a per- 

 manent and endemic inhabitant, a few words as to its distribution in the waters to 

 which the gulf is tributary will be germane. Originally supposed to be an Arctic 

 animal, this glass worm is now known to be cosmopolitan in the high seas from Arctic 

 to Antarctic; but except in high latitudes it is confined to waters so deep that it prob- 

 ably never reaches the Gulf of Maine from the oceanic basin abreast of it. Hence, 

 as Huntsman (1919, p. 476) points out. the Eukrohnia living in the upper 500 meters 

 or so (and this includes practically all the representatives of the species collected 

 either by the Gulf of Maine or by the Canadian fisheries expeditions) may be con- 

 sidered as distinctly northern. It is known to be common in the cool, heavy, mixed 

 water all along the continental slope from the Grand Banks of Newfoundland on 

 the north to the latitude of Chesapeake Bay to the south (fig. 93) in depths of 300 

 to 500 meters. For records of it east of Cape Sable see Huntsman (1919). How 

 universal it is along this zone abreast the mouth of the Gulf of Maine and thence 

 westward and southward in considerable depths will appear from the fact that it 

 has been detected in the towings from 250 to 1,000 meters at 9 out of 12 Grampus 

 and Albatross stations from 1913 to 1920, irrespective of the time of year (stations 

 10076, 10220, 10233, 10352, 10368, 10384, 10393, 20044, and 20077). 



Outside the Gulf of Maine it is probably more numerous below 400 meters than 

 above, for on February 22, 1920 (station 20044), none were found at 250-0 meters 

 when a number were taken in a haul from 750-0 meters. Again, on the slope abreast 

 of Cape Sable more Eukrohnia were taken in the haul from 800-0 meters on March 

 19, 1920 (station 20077), than from 500-0; and on July 21, 1914, none were taken 

 in a horizontal haul at 300 meters off the slope of Georges Bank at station 10218, 

 but several were had at 400-0 meters at a neighboring station (10220) at about 



