CERATIUM SPECIES OF CARNEGIE COLLECTION 



17 



numbers. In the Carnegie collection there were twenty- 

 six records of its occurrence--all rare. Eighteen of 

 these records were from net samples, eight from pump 

 samples. 



This species is undoubtedly a shade species, al- 

 though previously insufficient data have been at hand to 

 demonstrate this. JSrgensen (1920) foimd it in the Med- 

 iterranean at the deeper levels in the summer but attri- 

 buted this occurrence to another cause (see p. 12). 

 Nielsen (1934) considered it a shade species, although 

 'lis few data were from above the 50-meter level. Since 

 two of his three records for this species were from sta- 

 tions rich in plankton, however, the occurrence above 

 this level does not necessarily indicate that it is not a 

 shade species. The Carnegie records substantiate Niel- 

 sen's classification of this species as a shade species. 

 It was found more frequently with increase in depth 

 (table 5). 



Table 5. 



Records of occurrence of C. digitatum 

 at three levels 



A=Number of records. B=Per cent of total number of 

 samples collected at that depth. 



It is doubtful if C. digitatum prefers oligotrophic 

 water. Ten of the twenty-six Carnegie records were 

 from water containing less than 10 mg P04/m^. This 

 is not owing to the fact that most of the records are 

 subsurface records. The phosphate content of the sur- 

 face water at the stations where the species was foimd 

 shows the same distribution. Ten of these are below 

 10 mg and the rest above, with some as high as 42. The 

 surface temperatures at the stations where C . digitatum 

 occurred, varied from 22.°4 to 29.°4 C. The ranges of 

 environmental conditions in situ were as follows: tem- 

 perature, 12.°5 to 28.°5 C; salinity, 34.3 to 36.5 per 

 mille; pH, 8.16 to 3.39; phosphate, 3 to 46 mg P04/m3. 



Variation. --Very few variations have been reported 

 for this species, probably owing to scanty material. 

 Jorgensen (1920), however, described a variant, var. 

 rotundatum . found in the Mediterranean and also in the 

 Guinea Current. It is characterized by more rounded 

 apex, less bent apical horn, and somewhat larger size. 

 Peters (1934) stated that in the South Atlantic he found 

 specimens with more rounded epitheca than Jorgensen's 

 variety, fo the Carnegie collection two specimens were 

 found which answer well to Jorgensen's var. rotxmdatum . 

 They occurred in the surface samples frbm stations 52 

 and 54, both south of Easter Island in temperatures of 

 22.°5 and 23.°4C (figs. 5A and B). a is probable that this 

 form represents a species distinct from C. digitatum as 

 no intergrades were found between it and the typical 

 form. The typical C. digitatum does not vary greatly, 

 although the length of the left antapical horn varies 

 somewhat in different specimens (figs. 4C and E). 



5. Ceratium candelabrum (Ehrenberg) Stein 

 Figure 6, chart 5, appendix table 5 



This is a common, slightly tolerant tropical spec:es. 

 It is not confined to warm water. At Carnegie stations 

 the limits of distribution paralleled rather closely the 

 surface isotherm of 15° C in all three regions where the 

 lines of stations extended into colder regions, namely, 

 in the southeastern Pacific, off Japan, and off the west 

 coast of the Americas. These limits of distribution are 

 very significant, inasmuch as within these limits there 

 are extremely few stations without records of occur- 

 rence. At six stations off Peru it was not found, although 

 the surface temperatures there were above 19° C. Ap- 

 parently the peculiar environmental conditions in this 

 region have an inhibitory effect on C. candelabrum . In 

 the Atlantic the species occurred almost continuously in 

 the warmer water, but its northern limit there coincided 

 with the surface isotherm of 20° C rather than of 15° as 

 in the Pacific. In respect to latitude, C. candelabrum 

 was found approximately to 40° south and 40° north in 

 the Pacific, and to 42° north in the Atlantic. Its south- 

 ern limit in the South Atlantic is also at about 40° south 

 (Peters, 1934). Some of the stations of the Dana expedi- 

 tion extend, in the southwestern Pacific, beyond 40° south. 

 The southern records of C. candelabrum , however, end 

 at the fortieth parallel. This roimds out a remarkable 

 correlation between latitude and the distribution of a 

 Ceratium. It must be mentioned, however, that in the 

 southwestern Pacific, as well as in other parts of the 

 Pacific, the latitudes of 40° are closely paralleled bythe 

 surface isotherms of 15° C. 



This species is one of the most common of the genus. 

 In the Carnegie collection it was found at 136 stations -- 

 26 in the Atlantic and 110 in the Pacific. There were 353 

 records of occurrence--206 rare, 128 occasional, and 19 

 common. Of these, 243 were from net samples and 110 

 from pimap samples. 



In regard to vertical distribution, Neilsen (1934) 

 classified this species as a surface form. This classifi- 

 cation is substantiated by the Carnegie observations. As 

 can be seen in table 6, C. candelabrum was found most 

 frequently at 50 meters (44.2 per cent of the 50-meter 

 samples). It was found almost as often (36.0 per cent of 

 the surface samples) at the surface, but only half as fre- 

 quently at 100 meters (21.0 per cent). It is more signifi- 

 cant that the records of occasional and common occurred 

 much more frequently at the surface and 50 meters than 

 at 100 meters. 



Table 6. 



Records of occurrence of C. candelabrum 

 at three levels 



=Number of records. B=Per cent of total number of 

 samples collected at that depth. 



