50 



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



were above 20° C, except at station 66, where the tem- 

 perature was 19°.4 C. 



On the basis of these data, G. pacifica must be con- 

 sidered a strictly tropical species which does not endure 

 transfer to colder regions. For this reason it is a good 

 indicator of tropical water masses, although not so good 

 as Ceratocorys horrida because of its less frequent oc- 

 currence. 



Water of low nutrient content is no barrier to the 

 species, as there are 89 records of its occurrence in 

 water with less than 10 mg VO^/vcfi. 



The surface temperatures at the stations where the 

 species occurred at any depth varied from 19°4 to 

 29 °4 C. The ranges of hydrographic conditions in situ 

 were as follows: temperature, 1°.4 to 29°.3 C; salinity, 

 33.4 to 37.1 o/oo; pH, 7.17 to 8.39; phosphate, 3 to 121 

 mg P04/m^. 



Gonyaulax fusiformis n.sp. 

 (Figure 63) 



Dimensions . Length of the body (1^), excluding ant- 

 apical spine, 86 (67-98) microns. Diameter (d), 47 (35- 

 57) microns. Width of girdle, 4.8 (4-5.5) microns. 

 Length of antapical spine, 17 (12-23) microns. Seven 

 specimens were measured. 



Shape . Body broadly fusiform. The j/d ratio is 

 1.82 (1.68-1.98); thus body may be almost twice as long 

 as wide. Epitheca extended into a long apical horn equal 

 in length to rest of epitheca. Apex somewhat less than 

 1 girdle width in diameter. On left side, body tapers 

 gradually from girdle to apex, but on right side there is 

 a prominent shoulder as in Spiraulax. Hypotheca tapers 

 uniformly to antapex except for a constriction about 3 

 girdle widths from base of antapical spine (fig. 63D, E, 

 G). Body circular in girdle section (fig. 63B, F). Gir- 

 dle approximately equatorial, sinistral, displaced from 

 1.5 to 2.5 girdle widths, slightly concave; usually with 

 no overhang. Ventral area very narrow, usually almost 

 straight posteriorly, but bends to left anteriorly; some- 

 times slightly sigmoid. Posteriorly it flares out into an 

 elliptical area, similar to, but not so wide as, that in 

 Spiraulax . Anterior sulcal plate has an extension into 

 epitheca (as, fig. 63B). Flagellar pore a long, narrow 

 slit situated at left edge of ventral area between dis- 

 placed girdle ends and continued posteriorly about 1 

 girdle width. 



Plate pattern . The three apical plates quite unequal 

 in size. First apical is long, narrow, and curved, and 

 extends f(om apex to anterior sulcal plate on ventral 

 side of epitheca (fig. 63E). Second apical extends from 

 first apical around to dorsal side of body (fig. 63B); at 

 apex it has a limb (x, fig. 63B). about 1 girdle width 

 wide which fits Into a shoulder formed by the withdrawal 

 from the apex of the first anterior intercalary plate. 

 This process meets a similar process from the third 

 apical (y, fig. 63B, G). Body of third apical linear, ex- 

 tending along right side of distal half of first apical. 

 Therefore it lies between the first and second apicals 

 and between the apex and the two anterior intercalary 

 plates. The two anterior intercalaries make up the 

 greater part of right side of apical horn. The second of 

 them is on ventral face of body touching six different 

 plates, including first and third apicals, sixth precingu- 

 lar, and anterior sulcal plates. The six precingulars 

 are of approximately equal width except the first, which 



is somewhat wider. 



The six girdle plates approximately equal in length, 

 with sutures as shown by arrows in figure 63A. 



The six postcingular plates are about equal in width 

 except the first, which is small and narrow and lies 

 along left edge of flagellar pore (fig. 63E, F). A single 

 antapical plate extends almost halfway up the right side 

 of sulcus. It bears the heavy antapical spine and the 

 "sulcal spine" (fig. 63F, G). The posterior intercalary 

 forms the left edge of ventral area posterior to first 

 postcingular. 



Ventral area composed of six plates: anterior, pos- 

 terior, left, right, right accessory, and intermediate 

 (fig. 63C). Posterior accessory absent. Sulcal plate 

 has a projection into epitheca which meets the first api- 

 cal plate. A notch in posterior end of this plate repre- 

 sents anterior edge of flagellar pore as in G. p acifica . 

 Posterior sulcal plate comprises the expanded elliptical 

 posterior part of ventral area. It extends to within 1 

 girdle width of distal end of girdle. Left sulcal plate 

 forms posterior edge of flagellar pore and has a process 

 extending anteriorly along left edge of pore to meet first 

 postcingular plate, which also borders pore. Right and 

 right accessory plates form right edge of flagellar pore; 

 the right is opposite distal end of girdle; the right ac- 

 cessory is anterior to this. Intercalary sulcal plate is 

 small, square, posterior to right plate, and removed 

 from flagellar pore. 



Thus the flagellar pore is boimded by the first post- 

 cingular and four sulcal plates: the anterior, left, right, 

 and posterior accessory. The intercalary and posterior 

 sulcal plates do not touch the pore. 



Thecal wall . All plates of body except some of sul- 

 cal plates covered with a fine areolation which extends 

 completely to edges of plates. Most plates also bear a 

 few large, irregularly scattered pores, which, in optical 

 section, can be seen to pierce the body wall. They oc- 

 cur on the anterior, posterior, and left sulcal plates, but 

 frequently occur only In rows along the edges or ridges 

 of the narrower plates. One row occurs along each edge 

 of girdle plates. 



Intercalary zones occur along most of sutures and 

 are marked by a fine areolation and absence of pores. 

 Body ridges usually some distance from sutures, and the 

 intervening space may be considered the intercalary 

 zone, as it is probable that the ridge represents the o- 

 riginal suture line. 



The ventral epithecal pore so characteristic of Gon - 

 y aulax is present here at left anterior corner of second 

 anterior intercalary plate. Apical pore closed by a very 

 hyaline apical closing platelet. 



Lists. Girdle lists about 0.75 girdle width wide, 

 usually strengthened by simple ribs extending from body 

 to the edge of the list, spaced from 0.5 to 1 girdle width 

 apart (fig. 63A). Girdle plates free of ridges. Right and 

 left sulcal lists present. Posterior part of right sulcal 

 list attached to po6 and antl. A prominent, characteris- 

 tic spine, the sulcal spine, occurs in the middle of this 

 list at anterior corner of antapical plate. Anteriorly, 

 this list is continuous with posterior girdle list. Poste- 

 riorly it terminates at posterior end of ventral area. 

 The anterior (epithecal) part of right sulcal list is at- 

 tached to pr6 and as and is continuous posteriorly with 

 distal end of anterior girdle Ust. 



Although the boundaries of most of plates are Indi- 

 cated by ridges placed at some distance from the edges, 

 certain sutures are not so marked and extra ridges oc- 



