26 



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



Variation and comparisons . The variants of P. o- 

 ceanicum are innumerable. In the Carnegie material 

 all of them could be separated from the main species by 

 their shorter length (p. 23). These shorter forms, how- 

 ever, did not allow further segregation, although they 

 did not appear to present a homogeneous group. Hence 

 they were all lumped into the single variety treated 

 here. There was a great variation in the length, diver- 

 gence, and thickness of horns, and in the shape of the 

 mid-body. The numerous varieties of the species pre- 

 sented by other authors have usually been figured in on- 

 ly one position, viz., the resting position. The relation- 

 ships of these forms to each other and to var. tenellum 

 cannot be determined until statistical studies of body 

 shape are made. This, of course, cannot be done until 

 standard methods of presentation and measuring have 

 been adopted. 



Historical. Mangin (1913) described P. oceanicum 

 var. parvulum as a characteristic form at Saint- Vaast- 

 la-Hougue. Broch (1910b) described P. oceanicum f. 

 arupinensis as the typical form of the Mediterranean. 



The most commonly cited variant of P. oceanicum , 

 however, is P. oblongum Aurivillius (1898). The cur- 

 rent conception of this form seems to be that it is a 

 small neritic variety of P. oceanicum . If, however, we 

 are to accept the figures referred to by Aurivillius, we 

 must consider this form not only smaller than P. ocean - 

 icum . but of a somewhat different shape. Aurivillius 

 referred to figiires 39 and 40 of Bergh (1882) and fig- 

 ures 44,1 to 44,5 of Schutt (1895). In these specimens 

 the sides of the body are much straighter than in P. o- 

 ceanicum. and the apical horn is less definite. 



Some recent workers (e.g. Bohm, 1936) are includ- 

 ing under var. oblongum forms with very rounded bodies 

 and distinct, long apical horns. As stated above, the re- 

 lationships of these forms cannot be determined until 

 frequency studies have been undertaken. 



Broch (1910) stated that P. oceanicum and P. ob - 

 longum have a list only on the right side of the sulcus, 

 and that f. arupinensis differs in having lists on each 

 side. Our observations of P. oceanicum and its variants 

 showed that their morphology agrees with that of all oth- 

 er members of the section Oceanica in the presence of a 

 list on each side of the sulcus. This list is, however, 

 frequently difficult to demonstrate. 



Distribution . This variety is widely distributed. In 

 the Carnegie material it was found at 60 stations: 14 in 

 the Atlantic and 46 in the Pacific. There are 138 rec- 

 ords of occurrence: 85 rare, 48 occasional, 3 common, 

 and 1 abundant. It was found oftener in the upper levels, 

 with 56 records for the surface, 42 records for 50 me- 

 ters, and 39 records for 100 meters. It was found in 

 both hemispheres and in all months of the year. 



It occurred in widely scattered areas of the Atlantic 

 and Pacific oceans (fig. 20). In the Atlantic it was found 

 in the North Atlantic Drift, south of the British Isles, off 

 the southeast coast of Iceland, and in the Caribbean Sea. 

 In the Pacific it occurred at sH ■stations in the general 

 area between Ecuador and tl j Tuamotus, at Easter Is- 

 land, at three stations south of latitude 36° south, at 11 

 stations in the three equatorial currents in the central 

 Pacific, at 4 stations off Japan, and at 4 stations off the 

 west coast of the United States. 



It was found over a great range of hydrographic 

 conditions. The surface temperatures at the stations 

 where it occurred at any depth varied from 10°.3 to 



28°6 C. The ranges of hydrographic conditions ]n situ 

 were as follows: temperature, 6°7 to 28°.6 C; salinity, 

 32.7 to 36.5 o/oo; pH, 7.71 to 8.39; phosphate, 8 to 220 

 mg P04/m3. 



This form is apparently of world-wide distribution, 

 occurring in a wide range of hydrographic conditions. It 

 is noteworthy, however, that it was not found at the Car - 

 negie stations where the phosphate content of the water 

 was low, that is, less than 8 mg per cubic meter. This 

 correlation may be significant in explaining its distri- 

 bution, since in the warmer areas the phosphate content 

 is often less than 4 mg/m^. Type locality: Carnegie 

 station 14. 



Peridinium oceanicum forma spiniferum n.f. 

 (Figure 34) 



Dimensions . Length of body (i) 225 (209-241) mi- 

 crons. Diameter (d) 131 (122-140) microns. Width of 

 girdle about 5 microns. Three specimens were measured. 



Shape . The h/d ratio is 123 (1.19-1.29). The angle 

 OL is 112° (104°-124°). The a/d ratio is 0.47 (0.43- 

 0.52); the b/a ratio is 0.11 (0.09-0.14). The distinctive 

 feature of this form is the presence of an accessory 

 horn, usually spine -tipped, on the fourth apical plate ei- 

 ther in the center of the plate or anteriorly. In the spec- 

 imens observed, this feature did not entail any change in 

 plate pattern. 



Plate pattern . Of the three specimens recorded, 

 two showed the first symmetrical and one the first a- 

 symmetrical pattern. In one specimen there was a 

 lengthening of the suture between 3a and 4pr with con- 

 sequent shortening of the suture between 3pr and 4pr. 



Comparisons . This form has been placed in P. oce - 

 anicum because most of the specimens had an h/d ratio 

 greater than 1.20. Furthermore, the horns are attenu- 

 ated as in that species. The mid-body shows a certain 

 similarity to P. depressum in its strong depression, in- 

 dicated by the comparatively low angle a. . This is not 

 enough, however, to come wholly within the range of P. 

 depressum . 



Distribution. This is one of the diverse forms 

 which originate on the Grand Banks of Newfoundland, 

 where organisms are subjected to violent changes in en- 

 vironmental conditions (p. 19). It was found in the 50- 

 and 100-meter samples at station 13 on the Grand Banks 

 of Newfoundland in August 1928. The ranges of hydro- 

 graphic conditions in which it was found were as follows: 

 temperature, -1°.64 to -1°10 C; salinity, 33.4 to 33.6 

 o/oo; pH 7.87; phosphate, 59 to 63 mg P04/m3. Type 

 locality: Carnegie station 13. 



Peridinium oceanicum forma bisintercalares n.f. 



(Figure 35) 



Dimensions. Length of body (i) 203 (187-224) mi- 

 crons. Diameter of body (d) 105 (91-125) microns. 

 Width of girdle approximately 5 microns. Three speci- 

 mens were measured. 



Shape . Similar to P. oceanicum . The h/d ratio is 

 1.40 (1.38-1.41). The angle a is 128° (121°-135°). The 

 b/a ratio is 0.13 (0.13-0.15). 



Plate pattern . The tabulation of the epitheca in the 

 specimens examined was of the first symmetrical pat- 



