FAMILY GONYAULACACEAE 



49 



(fig. 62A). 



The six precingulars of rather unequal length. 



The six girdle plates subequal in size except for g6, 

 which extends from distal end of girdle well around to 

 dorsal side of body (fig. 62F); all U-shaped in cross 

 section (fig. 62B). 



First postcingular small; anterior to pol; forms 

 left edge of flagellar pore (fig. 62C, L). It is similar in 

 size and position to pol in Ceratocorys . Second to 

 fourth postcingulars larger; subequal in size; occupy 

 left ventral and left lateral regions of hypotheca (fig. 

 62G). Fifth and sixth postcingulars large; the fifth is 

 dorsal, the sixth lateral and ventral. The sixth is ex- 

 tremely compressed and forms the lateral keel of hypo- 

 theca. 



Posterior intercalary plate, a long narrow plate ex- 

 tending from pol along left edge of sulcus to antapical 

 plate (fig. 62A, C, H, G, L). It bears the wide left sulcal 

 list. 



The antapical plate constitutes the compressed ant- 

 apex. A corner of it extends almost halfway to girdle on 

 left side of body (fig. 62J). Other margins of this plate 

 more limited, especially ventrally, where a narrow 

 strip only 1 girdle width wide is visible (fig. 62C). This 

 plate bears the antapical spine at its left ventral corner. 



Ventral area composed of seven plates (fig. 62K, L); 

 anterior, posterior, right, left, right accessory, poste- 

 rior accessory, and intercalary. The anterior sulcal 

 plate consists of two inseparable parts. Posterior part 

 roundish, with semicircular notch posteriorly which rep- 

 resents anterior edge of flagellar pore. Anterior part 

 is a process extending into epitheca between base of 

 first apical and sides of a2 and pr6 (fig. 62C). Posteri- 

 or sulcal plate large, subtriangular, with oblique base 

 anteriorly where it borders left and intercalary sulcal 

 plates. Remaining five sulcal plates lie between the 

 anterior and the posterior; three on the right side, one 

 on the left side, and one in the middle. Those on the 

 right side, reading posteriad, are the right accessory, 

 right, and intercalary. Of these, the right accessory 

 and part of the right constitute the right edge of flagel- 

 lar pore. Posterior edge of pore formed by tip of pos- 

 terior accessory, which lies between rs, i, and Is, but 

 does not touch ps. Part of left edge of the pore formed 

 by extension of Is; the rest by pol. Thus, all sulcal 

 plates touch the pore except the intercalary and posteri- 

 or. 



Body wall . Many prominent narrow lists rim longi- 

 tudinally along body; some run whole length of epitheca, 

 others extend onlv a short distance from girdle. Most 

 of these "ridges' bear no relation to sutures although 

 they have been so confused in the past. Sutures are often 

 mariced by low, narrow ridges; sometimes one on each 

 side of intercalary zones. Second anterior intercalary 

 frequently has a double line, indicating some sort of 

 zone, running transversely through its middle. 



A ventral epithecal pore occurs on left anterior cor- 

 ner of second anterior intercalary plate. Apical pore 

 covered by closing platelet. Minute tubercles are scat- 

 tered over major plates rather irregularly, although 

 they have a tendency to be arranged in rows. Kofoid 

 (1911a) interpreted these as pores. Some of the sulcal 

 plates may have similar tubercles or, sometimes, faint 

 reticulations (fig. 62A). Girdle plates crossed trans- 

 versely by a varying number of ridges, usually spaced 

 about 0.5 girdle width apart. 



Lists . Although there are an excessive number of 



body lists in this species, the usual list systems are 

 rather poorly developed. Girdle lists small or absent, 

 never over 0.5 girdle width wide. Ribs and other struc- 

 tural differentiations are absent on these lists. The 

 only wide list of the species is the left sulcal list, which 

 in the broad ventrolateral aspect of body covers half of 

 ventral area posterior to distal end of girdle (fig. 62 A). 

 It is attached to right and anterior edges of posterior 

 intercalary plate (fig. 62L). Right sulcal list absent on 

 hypothecal part of ventral area, but the anterior right 

 sulcal list is well developed. It occurs on right edge of 

 epithecal extension of ventral area and is attached to 

 pr6. In apical view it is visible as a "spine" at distal 

 end of girdle (ar, fig. 62D). The body list along right 

 keel of hypotheca is well developed and may attain a 

 width greater than 1 girdle width. 



Antapical spine often curved to the right. Its length 

 varies considerably, viz., from 0.8 to 2.2 girdle widths. 

 It may bear small lists or large reticulations. 



Variation . In thin-walled specimens the second 

 anterior intercalary usually is quite hyaline and struc- 

 tureless. This may be the reason why this plate has 

 previously gone unnoticed, for in such cases it may eas- 

 ily be mistaken for a wide intercalary zone if careful 

 dissections are not made. 



There is considerable variation in shape of body; 

 for instance, the degree of compression in the girdle 

 region may be low (see fig. 62E), and the antapex may 

 be extended as a slight horn (fig. 62H). 



Distribution . Gonyaulax pacifica is a rare, seldom 

 reported species, although it has a wide distribution 

 over the tropical seas. Pavillard (1931) reported it 

 from the Atlantic and from the Mediterranean (1909, 

 1931). Previous to the Carnegie cruise it had beenfound 

 in the Pacific only at San Diego (Kofoid, 1907b) and in 

 the Indian Ocean only by Karsten (1907). Bohm (1936) 

 states it had never been foimd in the western Pacific, 

 and Matzenauer (1933) did not find it in the Indian Ocean. 



In contrast with this apparent rarity, the species 

 was found at 77 Carnegie stations: 15 in the Atlantic and 

 62 in the Pacific. There are 163 records of occurrence: 

 140 rare and 23 occasional. It was never common or 

 abundant. It was found less at the surface than at the 

 lower levels, with 19 records for the surface, 73 for 50 

 meters, and 71 for 100 meters. There are 107 net rec- 

 ords and 56 pump records. It was found in both hemi- 

 spheres and in practically all months of the year. 



Gonyaulax p acifica was found rather consistently 

 throughout the tropics, although there are many gaps in 

 its distribution (fig. 61). In the Atlantic it was found at 

 all stations south of station 15, although not at.station 

 24 or in the Caribbean. Although the records are not 

 continuous south of 40° north, it was not found north of 

 that latitude. 



In the Pacific the records are even less complete 

 than in the Atlantic. There is no significant geographic 

 grouping of the record stations, however, and it is prob- 

 able that the species is more uniformly distributed than 

 the present records indicate. It is equally common in 

 the western Pacific and in the eastern Pacific. It was 

 not found north of latitude 35° north nor south of 32° 

 south. 



Although the Carnegie records do not show a con- 

 tinuous distribution in the tropics, the limits of the dis- 

 tribution of the species show a close correlation with the 

 surface isotherm of 20° C (fig. 61). At the stations 

 where the species was found, the surface temperatures 



