42 



CERATIUM IN THE PACIFIC AND NORTH ATLANTIC OCEANS 



53. Ceratium horridum Gran 



Figures 23I-L, 24C-I, 25A-G, 



chart 44, appendix table 49 



This species comprises a variable and uncertain 

 group of the genus. The authors cannot agree with Jor- 

 gensen (1920), however, who combines this group withC^ 

 tenue . Peters (1934) followed Jorgensen's classification 

 but did not name or figure any of the forms of the inclu- 

 sive species. Paulsen (1930) and Nielsen (1934), on the 

 other hand, separated C. horridum from C. tenue . as the 

 authors have done in the present report. The two spe- 

 cies can be separated on the basis of body shape and cur- 

 vature of horns and also, in part, on the basis of size. 

 The different shapes can be seen by reference to figures 

 23 to 26. Ceratium horridum is larger than C. tenue . 

 having an average diameter of 44 microns as compared 

 with 37 microns for C. tenue. The extremes, however, 

 overlap, with a minimum of 30 microns for C. horridum 

 and a maximum of 45 microns for C. tenue. 



Ceratium horridum is made up of a number of vari- 

 able units; formerly separated as C. horridimi (C. inter - 

 medium) . C. moUe . and C. claviger . Nielsen (1934) still 

 considered C. claviger a species distinct from C. molle . 

 but in the Carnegie collection no evidence for this sepa- 

 ration was found. It seems best, therefore, to treat 

 these forms as varieties. 



Variety molle and var. claviger are tropical forms, 

 whereas var. horridum is more or less cosmopolitan. It 

 is probable that there are northern and tropical forms of 

 var. horridum which overlap in such a way that they are 

 not distinguishable. In any event, a certain difference 

 can be discerned between the cold- and warm -water 

 forms. In figures 24D and G are two specimens repre- 

 sentative of the cold-water form of the North Atlantic; 

 figure 24H shows a specimen from the warm Gulf Stream 

 or North Atlantic West Wind Drift. Peters (1934) found 

 the inclusive species widespread over the South Atlantic, 

 as did Nielsen (1934) in the South Pacific. 



The Pacific material is similar to that of the Atlan- 

 tic, at least in part. The variety in the Panama region, 

 for instance, (fig. 24E) is similar to the Gulf Stream 

 form. The Galapagos form (fig. 25B), on the other hand, 

 rather closely resembles the cold-water form of the 

 North Atlantic. In the cool water of the southeast Pacific 

 the variety was more robust and long-horned (fig. 25E). 

 In the Humboldt Current the variety was even more ro- 

 bust and the horns were more extended (fig. 25F). In the 

 warm equatorial waters it was slender and long-horned 

 (fig. 24C). In the cold waters of the cold North Pacific 

 region it was found only at three stations off the west 

 coast of North America, stations 126 to 128, and at one 

 station off Japan, station 114 (figs. 241, 25A). At these 

 stations the variety did not resemble the cold-water form 

 of the North Atlantic. It was slender and long-horned, 

 resembling much more the equatorial form of the Pacific 

 (figs. 24C, 25G). It was, however, much more spiny. 

 The surface temperatures at the eastern stations varied 

 from ll.°2 to 16.°4 C and at the station off Japan It was 

 19.°9 C. The differences between the forms of var. hor- 

 ridum in the northern Atlantic and northern Pacific is 

 another indication of the Isolation of the northern Pacif- 

 ic waters. Its absence in the most northern (coldest) 

 stations in this region, however, may be owing to the 

 temperat\ires, which were mostly less than 10° C. This 

 was lower than the temperatures of the northern Atlan- 

 tic where the variety occurred. 



Variety molle is simil<i.- to var. horridum but is 

 confined to the warm regions. Its occurrence in the Car- 

 negie collection was sporadic. Its most northern position 

 in the Atlantic was at station 3 (see fig. 25D). Here it 

 was rather robust but had the typical long horns. In the 

 warmer stations it was more slsnder and delicate (see 

 fig. 231). The Pacific form of var. molle was quite sim- 

 ilar to that of the Atlantic (see fig. 23K). 



Frequently varieties were found which were difficult 

 for the authors to assign to either molle or horridum. 

 Figures 25C and G show two such. In a sense these are 

 intergrades between the two varieties, but figure 25G 

 shows a specimen with extremely long and attenutated 

 antapical horns. Specimens such as this have been part- 

 ly responsible, perhaps, for the opinion that C. horridum 

 and C. tenue are part of the same species complex. It is 

 not likely, however, that this represents an intergrade, 

 as the origin of the horns and proximal curvatures are 

 different from those of C. tenue (cf. figs. 26C-D). 



Among recent workers, Melsen (1934) is the only 

 one who considered C. claviger Kofoid a separate spe- 

 cies. This opinion probably is owing to a lack of suffi- 

 cient material, as it is plain from the Carnegie material 

 that this form Is characterized only by the swollen ends 

 of the antapical horns. The body shape and origins of 

 horns may be that of var. horridum or var. molle (see 

 figs. 23J, L), 



The species as a whole Is not very common. It was 

 found at a total of eighty Carnegie stations- -twenty-eight 

 in the Atlantic and fifty-two in the Pacific. Since there 

 are apparently cold- and warm -water varieties of the 

 species, the ranges of temperatures for these stations 

 are not very significant. In the Atlantic the siu^ace tem- 

 peratures at the record stations varied from 8.°9 to 28.°5 

 C and in the Pacific from ll.°2 to 29.°4 C. The environ- 

 mental conditions In situ were as follows: temperature, 

 6.°3 to 29.°3 C; salinity, 31.7 to 36.8 per mille; pH, 7.68 

 to 8.39; phosphate, 4 to 233 mg P04/m3. 



The total number of sample records for the species 

 was only 149, of which 96 were rare, 38 occaslona4, 11 

 common, and 4 abimdant. The net records numbered 96; 

 the pump records, 53. 



Ceratium horrid\mi is not a species of oligotrophlc 

 water. Although it was found in some "barren" regions, 

 It occurred predominantly in richer waters. Only 16 of 

 the 149 records were in water containing less than 10 mg 

 P04/m3. 



The species is a decided shade form. In the cold- 

 water region of the North Atlantic it was found about 

 equally at the three levels, but elsewhere it was found 

 much more frequently at greater depths, particularly at 

 100 meters. The depth records for the species throughout 



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

 samples collected at that depth. 



