22 



STUDIES IN THE MORPHOLCX5Y, TAXONOMY, AND ECOLOGY OF THE PERIDINIALES 



Historical . Broch (1906) described this form as a 

 subspecies of P. depressum Bailey and later (1910a) 

 treated it as a distinct species. Paulsen (1908) judged 

 It to be a valid species, as did Pavillard (1931) and oth- 

 ers. Peters (1928), however, considered it to be com- 

 pletely within the variation limits of P. depressum . In 

 a study of a vast amoimt of antarctic material, he stated 

 that he found the form always had hollow horns, but in 

 one sample from the North Sea he found the horns some- 

 times solid and sometimes hollow. In all dimensional 

 ratios studied by him he foimd a variation frequency 

 which suggested the presence of only one systematic u- 

 nit. He did not consider the a/d ratio, however. 



A form resembling var. p arallelum was described 

 by Schimper (in Karsten, 1905) as P. antarctlcum . Pe- 

 ters (1928), who studied both northern and antarctic ma- 

 terial, considered these two forms to be identical. Mat- 

 zenauer (1933), however, treats antarctlcum as a forma 

 of P. depressum . Since there is no antarctic material 

 in the Carnegie collection, it was not possible to subject 

 this southern form to the analysis applied to var. paral - 

 lelum . with the result that no direct comparisons could 

 be made between the two forms. 



Distribution . Broch (1906) considered this form a 

 boreal or boreo-arctic species and stated that in 1905 it 

 did not come farther south along the Norwegian coast 

 than latitude 62° north. It must be remembered that he 

 was considering the solid-spined individuals which prob- 

 ably represent the extremes of the variety. Paulsen 

 (1908) stated that it occurred as far south as the Skag- 

 errack. It occurs in the Antarctic according to Peters 

 (1928) and in the Indian Ocean according to Matzenauer 

 (1933). The present records are the first for the Pacif- 

 ic. 



In the Carnegie collection this variety was found at 

 15 stations: 13 in the Atlantic, 2 in the Pacific. There 

 are 26 records of occurrence: 8 rare, 11 occasional, 7 

 common. It was found about equally at the three levels, 

 with 9 records for the surface, 9 for 50 meters, and 8 

 for 100 meters. There are 20 net records and 6 pump 

 records. It was found only in the northern hemisphere, 

 in the months from July to September. 



This variety had a distribution in the Carnegie col- 

 lection similar to that of the main species in that it was 

 found at widely scattered stations in the Atlantic but was 

 restricted in the Pacific (fig. 20). In the Atlantic it was 

 fotmd in the North Sea (station 6h), at the stations in the 

 region of Iceland, on the line between Iceland and the 

 Grand Banks of Newfoimdiand at all stations except one, 

 and as far south as latitude 11° north (station 23). It did 

 not occur, however, in a single surface sample south of 

 latitude 42° north (station 13a). In the Pacific it was 

 found only at two stations, viz., stations 128 and 130, off 

 California. 



The variety occurred in a great range of hydro- 

 graphic conditions. The surface temperatures at the 

 stations where it occurred at any depth varied from8!4 

 to 27° 2 C. The hydrographic conditions in situ were as 

 follows: temperature, -l.°6 to 22°4 C; salinity, 32.7 to 

 36.8 o/oo; pH, 7.87 to 8.26; phosphate, 5 to 176 mg 

 P04/m3. 



It is thus evident that this form cannot be considered 

 a strictly low-temperature variety, as Broch (1906) sug- 

 gested. It may have its origin and center of greatest 

 abundance in the cold regions, but it is highly euryther- 

 mal. It is hardly possible that var. parallelum repre- 



sents an ecological variant, since it often occiirs mixed 

 with P. depressum . 



Peridlnixim depressum var. rectius n.var. 

 (Figure 25) 



Dimensions . Length of body (1.) 124 (113-135) mi- 

 crons. Diameter of body (d) 84 (76-92) microns. Width 

 of girdle about 6 microns. Two specimens were meas- 

 ured. 



Shape . Lateral outline in ventral view almost 

 straight between girdle and bases of horns. This full- 

 ness of body results in high angle ol . The h/d ratio is 

 1.10 (1.07-1.19). The a/d ratio is 0.38 (0.37-0.38). The 

 b/a ratio is 0.17 (0.16-0.18). The angle oc is 120° (111°- 

 130°). In lateral view the apical horn is continuous with 

 the body lines. All horns relatively stout. Lengths of 

 antapical horns similar to those in P. depressum , but 

 there is little divergence in any direction. Body nar- 

 rower dorsoventrally than in P. depressum ; sometimes 

 narrow elliptical in apical view (fig. 25A). 



Plate pattern . The epithecal tabulation is of the 

 first symmetrical pattern. In our specimens the x-ra- 

 tio was +0.6 and +0.7. Tabulation of other parts as in 

 main species. 



Bodv wall . Intercalary zones wide. Plates thinner 

 and surface sculpturing much less developed than in 

 most specimens of P. depressum . Other details same 

 as in main species. 



Comparisons . This variety expresses a tendency 

 toward a dorsoventral flattening of the body, and a tend- 

 ency toward a loss of the strong depression of the body 

 which results in a decrease in the inclination of the gir- 

 dle. In all these characters it differs from both the main 

 species and var. parallelum . It is further differentiated 

 from var. parallelum in its longer and stouter antapical 

 horns. It is distinguished from var. convexius . de- 

 scribed below, by its straight, instead of conspicuously 

 convex, body contours. 



In general appearance var. rectius is similar to P. 

 oceanicum var. parvulum Mangin (1913) fromSaint- 

 Vaast-la-Houge. It differs from this principally in hav- 

 ing a low h/d ratio. The h/d ratios computed from 

 Mangin's figures range from 1 .24 to 1 .45, which places 

 var. parvulum definitely in the P. oceanicum group. 

 Fxirthermore, the sides of var. parvulum are more con- 

 vex than in var. rectius . Mangin did not show a side 

 view, nor did he state the degree of dorsoventral flat- 

 tening. (Fig. 10b, lOd of Mangin are ventral views 

 drawn from the dorsal side.) 



Distribution . This variety was found at only two 

 stations: stations 6 and 32, both in the Atlantic (fig. 20). 

 The former station was southwest of the British Isles 

 and the latter in the Caribbean Sea. At the northern sta- 

 tion the form was collected with the net at 50 and 100 

 meters, in May; at the southern station with the pump at 

 the surface, in October. It was rare in each case. The 

 ranges of hydrographic conditions at these stations were 

 as follows: temperature, 11°.3 to 28°.0 C; salinity, 35.5 

 to 36.0 o/oo; pH, 8.08 to 8.23; phosphate, 2 to 41 mg 

 P04/m3. 



The wide range in temperatures indicates that this 

 form Is eurythermal. Thus, var. rectius is probably a 

 rare but widely distributed variety of P. depressum Bal- 

 ley. Type locality: Carnegie station 32. 



