CERATIUM SPECIES OF CARNEGIE COLLECTION 



21 



in the eastern part of the South Equatorial Current and 

 at Australia, but not at the colder stations. He raised it 

 to the rank of an independent species, and separated it 

 from C. pentagonum on the basis of size of body and 

 thickness of walls. He gave the transdiameter of C. 

 subrobustum as 77 to 89 microns, and that of C. penta - 

 g onum up to 72 microns. In the Carnegie material the 

 transdiameter of C. robustum varied from 72 to 90 mi- 

 crons; those of C . pentagonum (excluding subsp. pacificum 

 n. subsp.) were from 38 to 66 microns. The transdiam- 

 eter of subsp. pacificum was 55 to 78 microns. 



Ceratium subrobustimi is probably rarer than C. 

 pentagonum but, nevertheless, it is much more wide- 

 spread than previously was supposed. In the Carnegie 

 collection it occurred at forty-five stations--two in the 

 North Atlantic, where it had not been found before, and 

 forty-three in the Pacific. There were eighty-one rec- 

 ords of occurrence: sixty-three rare, fifteen occasion- 

 al, and three common. Of these records, fifty were from 

 net samples, and thirty-one were from pump samples. 

 Unfortunately, when the routine examination of this spe- 

 cies was conducted, the independence of this species was 

 not realized, so the records of its occurrence are not 

 complete. For this reason, the peculiar clumping of the 

 stations in the Pacific must be considered artificial and 

 not representing exactly the actual distribution. 



It may be noted that the species is a warm -water 

 form, however, not extending into water of low tempera- 

 ture. The surface temperatures at the stations where it 

 occurred, were all above 20° C except in the southeastern 

 Pacific, where it was found at stations with surf ace tem- 

 peratures as low as 17° C. The ranges of environmen- 

 tal conditions in situ were: temperature, 14. °3 to 28.° 5 

 C; salinity, 34.0 to 39.8 per mille; pH, 7.17 to 8.39; 

 phosphate, 3 to 64 mg P04/m3. 



Nielsen (1934) stated that in the Dana collections C. 

 subrobustum was found only in the upper 50 meters. 

 The Carnegie data are at variance with this and strongly 

 suggest that the species is a shade species. As can be 

 seen from table 11, the species was foundmore frequent- 

 ly with increase in depth to 100 meters. Particularly 

 significant are the records of "occasional," which were 

 found in 0.3 per cent of the surface samples, 2.1 per 

 cent of the 50-meter samples, and 3.2 per cent of the 

 100-meter samples. In this respect C. subrobustum dif- 

 fers from C. pentagonum . which was found more fre- 

 quently at 50 meters. 



Table 11. 



Records of occurrence of C. subrobustimi 

 at three levels 



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

 samples collected at that depth. 



11. Ceratium teres Kofoid 

 Figures IIB-D, chart 11, appendix table 11 



This is a rare, slightly tolerant tropical species, 

 although widespread. to the Carnegie collection it 



occurred at sixty-two stations — twelve in the Atlantic, 

 and fifty in the Pacific. There were 106 records of oc- 

 currence, with 85 rare and 21 occasional. The species 

 is so small that it was collected more fre4uently in the 

 pump samples. There were 30 net records and 76 pump 

 records. Expressed in percentages these are 5.6 per 

 cent of the net samples, 20.8 per cent of the pump sam- 

 ples. 



In regard to geographic distribution, the species is 

 rather too irregular to draw any conclusions. Its ab- 

 sence is particularly noticeable, however, in the region 

 of Panama, Galapagos, and southward. It occurs, on the 

 other hand, at Easter Island and south to 40° south. 



Ceratium teres was mostly confined to warm water. 

 In the Atlantic the surface temperatures at its record 

 stations were all above 24.°8 C; in the Pacific, above 

 20.°6 C, except in the southeastern region where it was 

 as low as 15.°0 C (station 60). The ranges of environ- 

 mental conditions in situ were: temperature, ll.°4 to 

 29.°4 C; salinity, 33.9 to 37.1 per mille; pH, 7.99 to 8.39; 

 phosphate, 3 to 123 mg P04/m3. 



Ceratium teres does not avoid oligotrophlc water. 

 Forty-seven of the 106 records of occurrence were in 

 water containing less than 10 mg P04/m3. 



Nielsen (1934) found this species only in the sam- 

 ples taken from 50 to meters. In the Carnegie collec- 

 tion it was found about as frequently in the 100-meter 

 samples as in the samples from higher levels (table 12). 

 The surface contamination of the deeper nets, however, 

 must be taken into consideration here. 



Table 12. 



Records of occurrence of C. teres 

 at three levels 



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

 samples collected at that depth. 



12. Ceratium kofoidll Jorgensen 

 Figure IIH, chart 12, appendix table 12 



This is a very rare, slightly tolerant tropical spe- 

 cies, seldom collected because of its extremely small 

 size. In the Carnegie collection it was found at eight 

 stations in the Pacific. There were twelve records of 

 occurrence, ten of which were rare and two occasional. 

 It was found predominantly in the pump samples because 

 of the smaller mesh of the pump fUter net. Two of the 

 records were from net samples and ten were from pump 

 samples. 



The record stations for C. kofoidii were widely 

 scattered (chart 12). The surface temperatures at the 

 stations where It occurred, varied from 16.°2 to 27f 7 C. 

 The environmental conditions in situ were: temperature, 

 ll.°7 to 27.°6 C; salinity, 34.4 to 35.3 per mille; pH, 8.03 

 to 8.34; phosphate, 5 to 58 mg P04/m3. 



Six of the records were from surface samples, three 

 from 50-meter samples, and three from the lOO-meter 

 samples. Thus, it is probably a surface species. Four 

 of the twelve records were from water containing less 

 than 10 mg P04/m3. 



