species in a sample, the probability is high that there 

 will be P'2 Ri or even P3 Ri. Usually the rami are 

 detached between Rel-2 and Ril-2. 



The setae of the swimming legs are also fragile, and 

 usually broken at their own joints which occur at 

 about two-fifths the length of the seta. 



Spinncalanus and Monacilla species have strongly 

 developed rows of spines and spinules on the surface 

 (especially the posterior surface) of certain segments 

 in the swimming legs. These spines are also rather 

 fragile and are sometimes detached, usually leaving 

 small scars. Sometimes a spine becomes detached 

 while the appendage is being mounted on a slide, and 

 the spine may lie in an unnatural position. The posi- 

 tion, size, and shape of these spines and spine rows are 

 rather constant within species, but there is some 

 variability, especially in groups of smaller spines, 

 spinules, or denticles. Sometimes there are slight 

 differences between right and left legs in the same 

 specimen, generally involving only a numerical 

 difference in one or a few spines. 



About lO'^f of the specimens examined had actual 

 abnormalities of the swimming legs: a typical seta in- 

 stead of the modified sawlike terminal seta; a short 

 Re3 with a terminal arc of typical setae; loss of one or 

 more outer spines (Fig. 207); or an extra seta. The 

 other leg of the pair is usually typical, and both 

 should be examined. Certain of these abnormalities 

 could arise, if the fragile appendage is broken in a late 

 juvenile stage and does not develop normally in time 

 for the adult stage. 



Male P5 are usually not detached, although some 

 species have relatively long and fragile rami. In this 

 study, males with left Bl longer than right Bl are 

 termed "left-handed"; conversely, "right-handed" 

 males have right Bl longer than left Bl. Handedness 

 appears to be species-specific, and is also correlated 

 with the merging of segment 20 to 21 in the opposite 

 Al. 



The most important diagnostic characteristics of 

 the family and genera are in italics in the descrip- 

 tions. The species within each genus are numbered 

 and discussed in chronological order, including junior 

 synonyms which are placed in parentheses. 



surface layer is most responsive to local conditions; it 

 is cold (varying seasonally from —1.85° to 0°C) and 

 dilute (varies around 30°/oo), and usually well mixed. 

 The subsurface layer shows increasing salinity (to 

 about 33°/oo). The lower Arctic Water is transitional 

 to Atlantic Water. 



Freshwater, mainly from Eurasia, and low salinity 

 water entering the Arctic from Bering Strait (sill 

 depth about 100 m) form the Arctic Water. This layer, 

 nearly 200 m thick, flows under the influence of the 

 wind toward the basin exit between Spitsbergen and 

 Greenland. Some Arctic Water also leaves through 

 the channels between the Canadian Arctic Islands 

 and Greenland, flowing into Baffin Bay and Davis 

 Strait. There is a more or less closed clockwise move- 

 ment of this layer in the Canadian Basin (Beaufort 

 Sea), probably also a consequence of the wind 

 pattern. The sampling platform, T-3, has been caught 

 in this gyre. 



Under the general surface outflow is a subsurface 

 inflow of rather uniform Atlantic Water. This layer 

 has been defined as the warmer water (up to 2°C) ly- 

 ing between the upper and lower 0°C isotherms, 

 which occur at about 200 and 900 m. Most Atlantic 

 Water enters the Arctic between Spitsbergen and 

 Greenland (maximum sill depth 600-700 m, average 

 450-500 m) and flows eastward along the continental 

 slope of the Eurasian Basin. There is little seasonal 

 change in the temperature or salinity (about 35% o ). 



More than half of the volume of the Arctic Ocean is 

 Arctic Bottom Water, characterized by low 

 temperature (less than 0°C) and rather high salinity 

 (nearly 35% o ). Most of this water is probably formed 

 during the winter in the Norwegian Sea. The Bottom 

 Water in the Canadian Basin is slightly warmer than 

 that in the Eurasian Basin, since the source of the 

 former is at or above the level of the dividing ridge 

 (about 1,300 m). The pattern of movement of the bot- 

 tom water is unknown. 



There are no really sharp boundaries between these 

 simplified layers, especially at the far side of the Arc- 

 tic Ocean, in the Beaufort Sea, where the Atlantic 

 Water has had the maximum loss of its character and 

 where water intrudes from the Pacific. 



THE ARCTIC SPINOCALANIDAE 



Arctic Hydrography 



Coachman (1963) has reviewed the hydrography of 

 the Arctic Ocean. In general, there are three layers 

 (Fig. 3), based primarily on temperature and second- 

 arily on salinity: (1) Arctic Water, from the surface 

 to about 200 m, (2) Atlantic Water, from 200 to 900 m, 

 and (3) Arctic Bottom Water, from 900 m to the bot- 

 tom (maximum depth, over 5,000 m). 



The uppermost layer, the Arctic Water, is itself 

 composed of three layers: (1) surface, 0-25 or 50 m; (2) 

 subsurface, to 100 m; and (3) lower Arctic Water. The 



Vertical Distribution of 

 Arctic Spinocalanidae 



The low standing crop of phytoplankton in the 

 Arctic Ocean is attributed to the low submarine light 

 intensities; the photosynthetic production is probably 

 the lowest of anv comparable ocean area (English, 

 1963). 



Most early work on Arctic plankton, with the excep- 

 tion of Nansen's Norwegian North Polar Expedition 

 (1893-1896), was confined to sporadic, seasonal in- 

 vestigations of shallow waters of peripheral seas, es- 

 pecially in the Atlantic Sector, the Barents Sea, and 



