S117

Spongotrochus glacialis Popofsky group

Spongotrochus glacialis Popofsky, 1908, p. 228, pl. 26, fig. 8, pl. 27, fig. 1, pl. 28, fig. 2; Riedel, 1958, p. 227, pl. 2, figs. 1, 2, text-fig.

Spongotrochus glacialis Popofsky group, Petrushevskaya, 1975, p. 575, pl. 5, fig. 8, pl. 35, figs. 1-6

DESCRIPTION "Shell biconvex-discoidal, consisting of a spiny disc of spongy structure which is in some (fully developed ?) individuals surrounded by a lenticular lattice-shell. Spongy disc thickened in its central portion (a quarter to a half of its total diameter), with numerous acicular or acutely conical spines of different lengths around its circumference and in most specimens also on the two surfaces, particularly on the thickened central portion. When present, the enclosing lenticular lattice-shell is apparently in contact with the spongy disc at or near its circumference, but it is separated by a distinct space from its two surfaces. In most specimens, the spines arising from the thickened central part of the spongy disc penetrate the lattice-shell. The lattice-shell has an uneven surface, with subcircular or circular pores of varying sizes, the diameters of which are a half to ten times as great as the breadth of the intervening bars." (from Riedel, 1958).

DIMENSIONS "Diameter of shell 195-465 microns. Length of free parts of spines on circumference 5-170 microns (often about 70 microns)." (Riedel, 1958).

REMARKS 1. For further synonymy and taxonomic discussion see Petrushevskaya (1967, 1975) and Lozano (1974).

Plate 15, figures 2a-d

S118

RECENT DISTRIBUTION

1. Benson, 1966; "... rare but cosmopolitan in the Gulf [of California]." However, it is not certain if Benson's specimens belong to the same species as Riedel's Antarctic specimens.

2. Lozano, 1974, Fig. IV-12; "It is an important constituent of the radiolarian fauna in all of our samples. The higher percentage values are generally found under subantarctic waters where, with few exceptions, it constitutes over 10 percent of the total Radiolaria reaching a maximum value of 28.4 percent in core RC11-81.

"The 10 percent isopleth nearly coincides with the average position of the Antarctic Polar Front (APF). To the north only our samples between 35 degrees W and 25 degrees W and north of 40 degrees S have less than 10 percent of S. glacialis.

"The southern boundary of the area with more than 10 percent S. glacialis, being coincident with the average position of the APF, correlates well with the 5 degrees C February and 2 degrees C August sea surface isotherms. The northern limit of the area with over 10 percent S. glacialis cuts the isotherms and separates the subtropical Atlantic fauna with less than 10 percent S. glacialis from that of the subtropical Indian Ocean where it generally constitutes over 10 percent of the total Radiolaria."

3. Molina-Cruz, 1975, Code S44; mistakenly grouped with Spongopyle osculosa and Stylochlamydium venustrum. It appears now that each of these species has a defined distribution. Therefore, this category was not used in factor analysis of southeast Pacific assemblages.