S49

Ommatartus tetrathalamus tetrathalamus (Haeckel)

Panartus tetrathalamus Haeckel, 1887, p. 378, pl. 40, fig. 3; Nigrini, 1967, p. 30, pl. 2, figs. 4a-4d

Panartus tetrathalamus tetrathalamus Haeckel, Nigrini, 1970, p. 168, pl. 1, fig. 12

DESCRIPTION

"Terminology is that proposed by Riedel (1957, p. 76). Cortical twinshell constricted equatorially, with subcircular to subangular pores, having no definite arrangement, sometimes hexagonally framed; surface usually rough, spiny. Polar caps, when present, hemispherical to conical, approximately the same breadth as cortical twin-shell, supported by about 12 spines. Caps generally more delicate than twin-shell, with smaller pores and smoother surface. There are approximately equal numbers of specimens with and without single polar caps; rarely, completely or incipiently double-capped specimens are found. A few specimens have a delicate lateral meshwork supported by numerous rods, usually around the twin-shell, but sometimes extending around the caps. There is a tendency for middle latitude forms to develop rather stout unbranched spines, either on the distal ends of the cortical twin-shell or on the polar caps. Such forms are rare in low latitudes.

"Outer medullary shell lenticular, inner one spherical; radial beams connect outer medullary to twin-shell at the equatorial constriction." (from Nigrini, 1967).

DIMENSIONS

"Length of cortical twin-shell 90-136 microns; of polar caps 36-63 microns. Maximum breadth of cortical twin-shell 72-109 microns." (from Nigrini, 1967).

"cortical length 116 +/- 12 microns, cortical minimum width 83 +/- 5 microns microns, width at constriction 67 +/- 12 microns (based on 15 specimens)" (from Sachs, 1973).

REMARKS

1. For a more complete synonymy see Nigrini, 1967. The nominate subspecies permits distinction from O. tetrathalamus coronatus (see below). See Riedel (1971) for explanation of change in generic assignment.

2. Benson's (1966) description and detailed dimensions of this species (Zygocampe chrysalidium Haeckel in Benson, p. 193) are consistent with the above.

Plate 6, figures 1a-d

S50

RECENT DISTRIBUTION

1. Benson, 1966 (Zygocampe chrysalidium); "In the Gulf [of California] this species is cosmopolitan... It is rare in all stations except 90 (7.4%), 92 (2.4%), 184 (2.2%), 194 (7.5%) and 206 (3.0%)... In general, its frequency in the southern Gulf is slightly greater than that in the northern Gulf..."

2. Nigrini, 1967, fig. 13; "Indian Ocean occurrences - P. tetrathalamus is abundant in low latitudes, forming up to 29 percent (usually (9% to 22%) of the described population. South of 35 degrees S only a very few specimens have been observed. The species appears to be a reliable and potentially useful member of the low latitude assemblage."

3. Nigrini, 1968, text fig. 12; "Common to abundant throughout most of the equatorial region of the study area, decreasing in abundance to the north in the region of the North Equatorial Current and also in the 2 southernmost samples examined."

4. Nigrini, 1970, fig. 11; belongs to a tropical assemblage derived by recurrent group analysis of North Pacific samples, but ranges as far north as 40 degrees N right across the Pacific.

5. Sachs, 1973, Code 28I; counted together with O. tetrathalamus coronatus; "this species is essentially absent in the extreme Southeast, and is only significant (2.8%) at count [042], from RC12:403:TW:0-2.

6. Lozano, 1974, Fig. IV-6; "It reaches a maximum of 2.4 percent of the total radiolarian fauna in cores V29-80 and V27-191 under subtropical waters. It is found under the northernmost reaches of the subantarctic waters and in the eastern samples of the Atlantic Ocean, probably due to the Agulhas current influence.

"Minimum February sea surface temperature under which it is found is 8 degrees C (core RC11-67).

"West of 0 degrees C longitude, it may constitute more than one percent of the total radiolarian fauna only under February sea surface temperatures greater than 21 degrees C. East of 0 degrees longitude it may account for more than one percent of the fauna only under February sea surface temperatures greater than 17 degrees C."

7. Molina-Cruz, 1975, Code S23; counted together with O. tetrathalamus coronatus and used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S23 at each station. S51

8. Robertson, 1975; counted together with O. tetrathalamus coronatus; "This species loads most heavily in factor 2 (subtropical 25 degrees to 35 degrees N). At present, its greatest abundances are found to the extreme south and at 18,000 YBP comparable abundances are shifted about 5 degrees to the south."

9. Morley, 1977, Fig. I-13; counted together with O. tetrathalamus coronatus; "This species loads highest in factor 1 (tropical). At present this species occurs most frequently in samples from the central and western tropical and subtropical South Atlantic. It is absent in samples south of 35 degrees S. Although the 0% contour does not appear to be displaced northward at 18,000 YBP, the lack of samples in the subtropical and western tropical regions make it difficult to assess any possible changes in distribution pattern at this level."