38 



CERATIUM IN THE PACIFIC AND NORTH ATLANTIC OCEANS 



are much more abruptly turned anteriorly and all their 

 horns are thinner (cf. figs. 21E and F). 



The species as a whole is one of the most common 

 of the genus. It was found at 148 stations--42 in the At- 

 lantic and 106 in the Pacific. It was found frequently in 

 all the samples from a station so that the total number 

 of sample records for the species is large, namely, 482. 

 Of these, 226 were rare, 201 occasional, 54 common, 

 and 1 abundant. Net records predominated, of which 

 there were 307 as compared with 175 pump records. 



When dealing with a species as common as this one, 

 a series of negative records is significant. In this con- 

 nection it is Interesting to turn to the distribution of the 

 species in the North Pacific (chart 37). Subspecies gal- 

 licum was found at every station in the warm Pacific re- 

 gion except one off Japan, where its northern distribution 

 in the west ended abruptly at about 38° north latitude. In 

 the east, off California, the northern limit was equally 

 abrupt but there it was above 40° north latitude, with one 

 station in the cold North Pacific region. Otherwise, no 

 representative of C. macroceros was found in the cold 

 North Pacific region. The absence of subsp. macroceros 

 in this area is a good indication of the planktologlc iso- 

 lation of the North Pacific (see p. 11). 



In the South Pacific in this species we find evidence 

 of the continuity of the colder waters of all the southern 

 oceans. In the extreme southeastern part of the area 

 traversed by the Carnegie the species assumed the as- 

 pect of subsp. macroceros (fig. 21C). This is possibly 

 the southern form mentioned by Peters (1934) from the 

 Atlantic. 



Subspecies g alllcum may be classified as slightly 

 tolerant tropical . Off Japan it extended into water with 

 surface temperature of 19.°9; off the west coast of Amer 

 ica to temperature of 16.°4, and in the southeast Pacific 

 to 15.°0 C. In the Atlantic subsp. galllcum occurred at 

 surface temperatures of about 20° C, except at station 

 13, where the temperature was 11. °3 C. 



The ranges of environmental conditions in situ were: 

 temperature, -l.°6 to (29.°4) C; salinity, 31.7 to 37.1 per 

 mUle; pH, 7.17 to 8.47; phosphate, 2 to 123 mgP04/m3. 



It should be noted that the species was not found at a 

 line of stations off Peru nor between the Galapagos Is- 

 lands and Panama with the exception of two stations. The 

 waters here, especially off Peru, are eutrophic; the phos- 

 phate content in the upper 50 meters is mostly above 50 

 mg P04/m3. Is it possible that this accounts for the ab- 

 sence of C. macroceros? The temperatures at these sta- 

 tions were mostly above 20° C, so temperature hardly 

 can be responsible. Possibly C. macroceros avoids high 

 concentrations of nutrients. In this connection it should 

 be noted that in the North Atlantic, where C. macroceros 

 occurs at low temperatures, the phosphate content in the 

 upper 50 meters is mostly below 50 mg, whereas in the 

 northern North Pacific, where the species is absent, it 

 ts mostly above 100 mg. These conditions must be taken 

 Into account in any attempt to explain the distribution of 

 this species. It was pointed out in the general discussion 

 (p. 7), however, that it Is not likely that the concentra- 

 tion of such plant nutrients as phosphate and nitrate found 

 In the oceans are important in the qualitative distribution 

 of Ceratlum species. 



Ceratium macroceros occurs rather uniformly down 

 to the 100-meter depth. Nielsen (1934) found it mostly 

 above SOmeters, but in the Carnegie collection the great- 

 est percentage was at 50 meters, with slightly lower per- 

 centages at the surface and 100 meters (table 39). 



Table 39. Records of occurrence of C. macroceros 

 at three levels 



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

 , samples collected at that depth. 



47. Ceratium massiliense (Gourret) Jorgensen 

 Figures 22E-L, chart 38, appendix table 43 



Ceratium massiliense is one of the most variable 

 and difficult species of the genus. The typical form is 

 shown in figure 22F (which, incidently, is a two -celled 

 chain). It has the most common form of body, although 

 the horns frequently are much shorter. Variety armatum 

 (Karsten) Jorgensen is shown in figure 22L. This was 

 rare in the Carnegie collection. Peters (1934) consid- 

 ered it to be a cold-water subspecies in the South Atlantic, 

 but in our collection no correlation with lower tempera- 

 ture was evident. Variety protuberans (Karsten) Jorgen- 

 sen is another variation of the species which has been 

 recorded in the literature. It has a somewhat elongated 

 body and thin antaplcal horns, which are somewhat more 

 widely spread than in the typical form (fig. 221). There 

 is a form in the Atlantic which simulates somewhat C. 

 deflexum (fig. 22H). This probably accounts for Peters' 

 (1934) including C. deflexvun in the species C . massiliense 

 (see next species below). It will be noted that in this va- 

 riety of C. massiliense the left antapical horn, where it 

 leaves the body, is directed slightly antapically so the 

 posterior curvature of the horn and the posterior edge of 

 the body are not in the same line. The right antapical is 

 directed somewhat more posteriorly than in the main 

 form of the species. This type of divergence, as regards 

 antapical horns, may be accentuated even more, so that 

 the specimens resemble, to a degree, C. macroceros (fig. 

 22G). In this case the curvatures of the antapical horns 

 extend to a distance about 0.5 transdlameter beyond the 

 body. A variation of this is shown in figure 22J in which 

 the right horn does not extend far posteriorly but later- 

 aUy. Still another variation was found in which the ori- 

 gins of the antapicals are more lateral than in the main 

 species, and the horns themselves are much more wide- 

 spread (fig. 22K). 



Most of the Carnegie material of this species could 

 be placed in one of the above nine varieties. Inter grades 

 were fairly common, however, so the complex as a whole 

 represents a single variable species. The varieties 

 showed no correlation with geographic position or hydro- 

 graphic conditions, except that the defleximi type was 

 confined to the Atlantic. 



There is also a form which tends toward the body 

 shape of C. contrarlum (fig. 22E). The left antapical 

 leaves the body in line with the posterior edge of the body; 

 the right extends somewhat posteriorly. The horns are 

 slender. A four-celled chain was found in this form. 



The species, as a whole, is one of the most common 



