N1

Antarctissa denticulata (Ehrenberg)

Lithobotrys ? denticulata Ehrenberg, 1844b, p. 203

Antarctissa denticulata (Ehrenberg), Petrushevskaya, 1967, p. 87, fig. 49, I-IV

DESCRIPTION

"The skeleton is massive, has a characteristic equilateral triangular outline. The first segment is small, deeply submerged into the widenend second segment.

"The width of the second segment has a ratio of 1.5-1.8 : 1 to the width of the first segment. The widest part of the shell is at the lower part of the second segment. The "thorax" is closed below by a flat plate, perforated by pores. The pores on the shell are oval, randomly arranged, somewhat larger on the second segment. The shell walls are very thick and consequently the pores form in them a structure, which has a morphology reminiscent of funnels. The shell surface is rough, with thorns. The longer thorns are situated on the lower edge of the shell. The spines of the inner skeleton, A, Vert, D, Lr and Lj, are very tightly connected to the shell walls. Their extensions are almost unnoticeable on the outside of the shell." (from Petrushevskaya, 1967; translation courtesy W.R. Riedel).

DIMENSIONS "Length of the first segment (externally) 35 microns - 50 microns, width 65 microns - 80 microns, length of the second segment 70 microns - 90 microns, width 90 microns - 150 microns." (from Petrushevskaya, 1967; translation courtesy W.R. Riedel).

REMARKS

1. For further synonymy and description of 3 additional varieties see Petrushevskaya (1967).

2. "A form with three segments...is present but only a few specimens were observed in all the samples. Evidently it is closely related to A. denticulata but because it has three segments it would have to be classified in another genus or the definition of the genus would have to be expanded to include forms with three segments." (from Lozano, 1974).

Plate 18, figures 1a,b

N2

RECENT DISTRIBUTION

1. Riedel, 1958 (Peromelissa denticulata); "...occurs in both the American and Indian Ocean sectors of Antarctic waters, and no form closely resembling it has been found at any other locality. Thus it appears to be an exclusively southern cold-water species."

2. Hays, 1967, Fig. 5 (Peromelissa denticulata); "The distribution of Peromelissa denticulata is nearly identical to that of Helotholus histricosa...P. denticulata is usually less abundant; however, there is one striking exception to this generalization that may be of some significance. The two Deep Freeze samples located in the Ross Sea and the Russian sample Ob-282 have an assemblage in which Peromelissa denticulata is dominant. Since the number of individuals in these samples is not great and only three samples from the shelf were examined, no conclusions can be drawn; however, it may be that this species is more tolerant of near-ice conditions than the other members of the Arctic fauna.

"Peromelissa denticulata has not been reported from outside the Antarctic and, with the exception of cores raised from the Argentine basin, was not encountered in this study north of the mixed zone. It ranges back to zone phi, but its occurrence there is rare."

3. Lozano, 1974, fig. IV-17; the typical form and three varieties described by Petrushevskaya (1967) were counted together.

"It is more abundant under Antarctic waters reaching a maximum of 26.4 percent in core V15-133. Values over 10 percent are found south of the APF and as far north as 45 degrees S in the Atlantic Ocean. Its abundance decreases under sub-antarctic waters and it is practically absent at the average position of the subtropical convergence, except in the northern part of the Argentine and Crozet Basins.

"In the Argentine Basin the correlation of percentage of A. denticulata and the 5000 m water depth is striking. North of 47 degrees S sediments from water depths greater than 5000 m have percentages generally greater than 5 and as high as 15.8 whereas samples shallower than 5000 m have values generally under one percent. It is also evident (Fig. IV-17) that the values are generally higher in the western side of the basin. This pattern of distribution is best explained by bottom transport of this species by Antarctic Bottom Water in the Argentine Basin...

"The distribution of A. denticulata indicates that north of 47 degrees S the bottom currents are strong enough to transport Radiolaria only at water depths greater than 5000 m. In the western margin of the basin the N3 influence of the bottom current is evident at shallower depths (Lloyd Burckle, personal communication). We have only one sample at 4401 m (V18-153 at 35 degrees S in which A. denticulata accounts for 4.7 percent of the total Radiolaria. A similar pattern is discerned in the Crozet basin. Here the percentage values are lower than in the Argentine basin and the influence of bottom transport is felt at depths shallower than 5000 m in the western part of the basin where practically all out cores are located. There is also evidence of northward transport in the Aguhlas basin.

"Outside the Argentine and Crozet basins, A. denticulata is never found in proportions larger than one percent under August sea surface temperatures over 8 degrees C. It is occasionally found in small proportions under the warmer waters in the Indian Ocean but it is absent in the three samples east of the Crozet basin.

"In the Atlantic Ocean, east of 30 degrees W it is practically absent under August sea surface temperatures over 10 degrees C.

4. Morley, 1977; see Antarctissa strelkovi.