34 



STUDIES IN THE MORPHOLCX3Y, TAXONOMY, AND ECOLOGY OF THE PERIDINIALES 



opment of the lists of the body. The right spine varies 

 in length from 7 to 17 microns. 



Comparisons . This is the only species of the para 

 group included in this report. It is of particular inter- 

 est to compare the ventral area of this species with that 

 of species of other parts of the genus. Previous inves- 

 tigators have considered Paraperidinium more closely 

 related to Metaperidinium than to Orthoperidinium. An 

 examination of the ventral areas of the representatives 

 presented in this report, however, indicates that Para - 

 peridinium is more closely related to the ortho group 

 than to the meta. Although the ventral area of P. palli - 

 dum is distinctive, it resembles in general that of P. 

 depressum more than that of P. crassipes or that of P. 

 truncatum . The entire ventral area is depressed in P. 

 pallidum, so that it does not take part in the major body 

 plate complex. In this respect P. pallidum resemblesP. 

 depressum . Similarly, the ventral area is bordered by 

 the primary sulcal lists rather than by the accessory 

 ones, even though the right sulcal list may be double in 

 specimens with intercalary zones. The ventral area of 

 P. pallidum differs from that of P. depressum signifi- 

 cantly only in the absence of the right internal sulcal 

 plate and in the presence of the right accessory sulcal 

 plate. Its only resemblance to that of P. crassipes and 

 to that of P. truncatum is in the relative position of the 

 sutures between the first and fifth postcingulars and the 

 antapical plates. These sutures join the ventral area a- 

 bout halfway between the antapex and the girdle, instead 

 of near the posterior end of the area as in P . depressum . 



The absence of antapical horns does not seem to al- 

 ter the structure of the ventral area in any fundamental 

 way. 



Of the species so far analyzed, this is the only one 

 in which the sutures between the girdle plates are so 

 near the ventral area, that is, in which the second and 

 fourth girdle plates are so short. In other species these 

 sutiires are in line with the sutures of the major body 

 plates. 



Historical . This species is very closely related to 

 P. pellucidum (Bergh) Schutt and, in fact, may include 

 that species. If so, the name pellucidum has priority 

 (Bergh, 1881). In her comparison of these two species, 

 Lebour (1925) gives size and shape differences: P. pel- 

 lucidum . length 40-68 microns (without spine?), breadth 

 36-70 microns; P. pallidum , length 70-96 microns, 

 breadth not stated. In the Carnegie material the h val- 

 ues vary from 38 to 107 microns with no grouping of 

 the values that would suggest the presence of two spe- 

 cies or varieties. The diameters vary, similarly, from 

 35 to 98 microns. Only eighteen specimens were meas- 

 ured, however, and it is possible that additional materi- 

 al would indicate the possibility and desirability of sep- 

 aration. Lebour (1925) states that the compression is 

 very slight in P. pellucidum and gives a figure with cir- 

 cular girdle section (pi. 28, figs. 2c, 2d). In the Carne - 

 gie material the g/d ratio was found as high as 0.90, 

 and this was not correlated with small size but, on the 

 contrary, was found in one of the largest specimens of 

 the coUecUon. Lebour gives the theca as finely reticu- 

 late for P. pellucidum but gives no figures. Peridinium 

 pellucidum is supposed to be a neritic form (Lebour, 

 1925) and thus would not be expected to be found in the 

 Carnegie material. 



In our opinion the existence of two separate forms 

 must be held in doubt until a further study is made of the 

 small neritic forms. If they are distinct from the form 



found in the Carnegie material, then other characters 

 than size and shape must be found to distinguish them. 



Distribution . Common in the northern North Atlan- 

 tic (Paulsen, 1908; Lebour, 1925). Reported from the 

 Mediterranean by Forti (1922). Rare in the Antarctic 

 (Peters, 1928). Not reported from the Indian Ocean by 

 Matzenauer (1933) nor from the Pacific by Bohm (1936). 



In the Carnegie collection this species was found at 

 28 stations; 16 in the Atlantic and 12 in the Pacific. 

 There are 57 records of occurrence: 27 rare, 28 occa- 

 sional, and 2 common. It was found about equally at the 

 three levels although somewhat more frequently in the 

 upper levels, with 22 records for the surface, 20 for 50 

 meters, and 15 for 100 meters. There are 44 net rec- 

 ords and 13 pump records. It was found mostly in the 

 northern hemisphere, with only 1 station in the southern, 

 and from May to September. 



In the Atlantic it occurred at most of the northern 

 stations and as far south as 34° north (station 17). In 

 the Pacific it was found at three series of stations: off 

 Japan (stations 113-114, 116-117); between San Francis- 

 co and Honolulu (stations 133-137); and in the western 

 series crossing the equatorial currents (stations 97-98, 

 101-102). There was no center of abundance; the rec- 

 ords of "occasional" were scattered over its range. 



The surface temperatures at the stations where this 

 species was found at any depth varied from 8°.4 to 28°3C. 

 The ranges of hydrographic conditions in situ were as 

 follows: temperature, -1°.6 to 28°.3 C; salinity, 33.4 to 

 36.6 o/oo; pH, 7.87 to 8.47; phosphate, 3 to 99 mg 

 P04/m3. 



Peridinium pallidum is probably a widespread spe- 

 cies of sporadic occurrence. It can endure a wide range 

 of hydrographic conditions, and factors limiting its pro- 

 duction are not indicated in the present data. It can de- 

 velop in low concentrations of nutrients, as is shown by 

 19 records in water with less than 10 mg P04/m3. 



Family CERATOCORYACEAE Lindemann 



Diagnosis . Shape angular to rounded, no prominent 

 horns. Epitheca rounded, hornless, spineless, usually 

 low. Hypotheca angular to rounded, usually bearing 

 prominent spines. Girdle anterior to equator, sinistral, 

 not concave, without overhang. Ventral area narrow, 

 depressed anteriorly; flagellar pore at anterior end. 

 Girdle and sulcal lists well developed. Ventral epithe- 

 cal pore present on a2. Plate formula: apical closing 

 platelet, 2ap, 2a, 5pr, 6g, 5-6po, Ip, lant, 5-6s. Marine. 



Only one genus, which includes seven species. 



Genus CERATOCORYS Stein 

 Diagnosis 

 See family diagnosis (monogeneric) 



Description 

 Size . Length of body (i) varies from 38 microns in 

 C. gourretii to 99 microns in C. armata . Width at gir- 

 dle in ventral view (d) from 28 microns to 114 microns 

 in the same species, respectively. 



Shape . Body angular in all species except C. gour - 

 retii . C. horrida being the most angular. At girdle, body 

 is squarish to circular or subovate. Girdle placed al- 

 most equatorially in C. armata and C. reticulata , in all 



