CERATIUM SPECIES OF CARNEGIE COLLECTION 



15 



Table 2. Records of occurrence of C. praelongum 

 at three levels 



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

 samples collected at that depth. 



Although C. praelongum was limited to warm water 

 it did not show any preference for oligotrophic water. 

 Only sixteen of the sixty -seven records were in water 

 containing less than 10 mg P04/m3. The surface tem- 

 peratures at the stations where it occurred, varied from 

 20.°4 to 29.°4 C. The ranges of environmental conditions 

 in situ were: temperature, 14.°2 to 29.°4 C; salinity, 33.4 

 to 37.1 per mille; pH, 7.87 to 8.47; phosphate, 2 to 63 

 mg P04/m3. 



Remarks . - -Dissections were made of the plates of 

 C. praelongum . The pattern Is shown in ventral and left 

 lateral views in figures 1 A and B. It will be noted that 

 in this species two apical plates touch the ventral area, 

 whereas Jorgensen (1911) stated that in the subgenus 

 Poroceratium only the large flat ventral apical touches 

 the ventral area. Kofoid (1907b) devised anomenclature 

 for the plates of Ceratium. For Poroceratium he start- 

 ed nimibering the apical plates with the wide ventral 

 one, basing his system on the pattern of C. gravidum in 

 which this plate is the only one to touch the ventral area. 

 Thus he called this one the apical plate. Jorgensen (1911), 

 on the other hand, called it apical four. A knowledge of 

 the pattern of C. praelongum . a member of Porocera- 

 tium . shows that Jorgensen's system is preferable In 

 that it indicates homologies. The Suture in C. praelon- 

 gum . which separates the ventral and left apical plates, 

 is homologous with the ventral suture of C. tripos , 

 which separates the first and fourth apicals, so that the 

 ventral plate of Poroceratium is homologous with the 

 fourth of C. tripos and should be designated apical 4 

 as in Jorgensen's system. Ceratium praelongum . in its 

 epithecal plate pattern, is thus transitional between 

 other members of Poroceratium and Euceratium. 



Variation. - -There is considerable variation in the 

 shape of the body of C. praelongum but the variants 

 seemed to bear no relation to geographic location or en- 

 vironmental conditions. The forebody may be constrict- 

 ed just anterior to the girdle as in figure lA, or in the 

 middle region (fig. IC), or may be quite regular as in 

 figure ID. The last figure shows an individual with very 

 heavy hypothecal walls and thick antapical horns. None 

 of the variations found could be satisfactorily grouped 

 into varieties. 



2. Ceratium cephalotum (Lemmermaxm) Jorgensen 

 Fig^ure 2, chart 2, appendix table 2 



This is a rare, intolerant tropical species. Jorgen- 

 sen (1911) stated that it has been reported from the 

 North Atlantic only north of the West Indies; Peters 

 (1934) found it only at one station in the South Atlantic. 

 In the Carnegie collection it was found in the Atlantic at 



two stations between the North Atlantic Drift and the 

 Sargasso Sea at 100 meters in both cases. 



The species is never found in great numbers, fii 

 the Carnegie collection it was found at a total of thirty- 

 two stations; two in the Atlantic, thirty in the Pacific. 

 There were thirty-nine records of occurrence- -thirty- 

 six rare and three occasional. Thirty-six of the records 

 were from the net samples; three from the pump sam- 

 ples. 



Ceratium rephalntiim is a shade species according 

 to Nielsen (1934), and this classification is substantiated 

 by the Carnegie data as shown in table 3. It was found 

 in an increasing percentage of the samples with increase 

 in depth. Although Nielsen found it only in the samples 

 taken between 100 to 50 meters, in the Carnegie collec- 

 tion it was found almost as frequently at the surface as 

 at 50 meters. 



Table 3. 



Records of occurrence of C. cephalotum 

 at three levels 



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

 samples collected at that depth. 



The Carnegie data suggest that this species prefers 

 oligotrophic water. It is always found in warm water. 

 The surface temperatures of the water at the stations 

 where it was found varied from 23.°6 to 29.°4C. Twenty- 

 four of the thirty-nine records were in water containing 

 less than 10 mg P04/m3. It is particularly noteworthy 

 -in this connection that the species was found m a contin- 

 uous series of stations north and east of Hawaii and all 

 are included in the great "desert" of the North Pacific. 

 Peters' (1934) record for the South Atlantic was also in 

 oligotrophic water. The ranges of environmental condi- 

 tions m_situ were: temperature, 13.°8 to 28.°7C; salinity, 

 34.1 to 36.5 per mllle; pH, 8.17 to 8.47; phosphate, 4 to 

 36 mg P04/m3. 



Ceratium rep halntinn is not very variable. Some- 

 times the overgrowth of the right side is less pronounced 

 (fig. 2B). 



3. Ceratium gravidimi Gourret 

 Figures 3 and 4, chart 3, appendix table 3 



This is a relatively rare, but widespread, slightly 

 tolerant tropical species found at most of the Carnegie 

 tropical stations. Peters (1934) found It only in warm 

 oligotrophic water in the South Atlantic. In the Carnegie 

 collection it was found at most (seventeen) of the twenty- 

 three stations in the warm Atlantic region. It was not 

 found at any Atlantic station where the surface tempera- 

 ture was less than 20° C. All the Atlantic stations were 

 in oligotrophic water with phosphate content less than 10 

 mg at the surface, except at station 1 where it was thirty- 

 two. The temperature there, however, was 24°. 



In the Pacific Nielsen (1934) found C. gravidum in 

 both eutrophic and oligotrophic water at scattered stations 



