S119

Spongotrochus (?) venustum (Bailey)

Perichlamydium venustum Bailey, 1856, p.5, pl. 1, figs. 16, 17

Stylochlamydium venustum (Bailey), Haeckel, 1887, p. 515

DESCRIPTION "Shell is a spongy, biconvex, circular disc; surface rough. Central structure probably a single lattice sphere, but generally obscured by spongy meshwork. In well-preserved specimens, broken concentric rings visible and a pored equatorial girdle. Cylindrical radial spines, probably originating from central capsule, lie on the equatorial plane (or nearly so) and extend beyond the marginal girdle." (Gail Lombari, unpublished data).

DIMENSIONS "Based on 20 specimens; shell diameter 120-192 microns for all specimens; shell diameter of complete specimens 175-192 microns." (Gail Lombari, unpublished data).

REMARKS

1. Most recent radiolarian workers have followed Haeckel's taxonomy with regard to this species, i.e., Stylochlamydium venustum (Bailey). However, because the species is composed of a spongy framework and does not have a porous sieve plate, the genus Stylochlamydium is unacceptable. The genus Spongotrochus has been suggested herein because of the apparently close relationship between this species and Spongotrochus glacialis.

2. According to Renz (1976), "in most specimens the concentric rings appear "broken" in a spongy meshwork; and the equatorial girdle is present."

Plate 15, figures 3a,b

S120

RECENT DISTRIBUTION

1. Sachs, 1973, Code 17I (Stylochlamydium venustum) Fig. 2c; "In the present study, two forms corresponding approximately to Stylochlamydium venustum or Spongotrochus ? glacialis were separately tabulated. The former generally includes forms lacking a pylome, but often with protruding spines on the periphery. The latter always showed a marked pylome, but generally lacked spines...These two categories have been combined in the results reported here. Because of the abundance of these forms, more detailed resolution of taxa is potentially most valuable. However, it has not yet been possible to recognize more detailed divisions in all specimen orientations, which is required for the counting undertaken in this study...

"Ubiquitous and very abundant, but most strongly associated with the Subarctic Factor (Factor 2), which reaches its maximum expression at intermediate latitudes."

2. Molina-Cruz, 1975, Code S44 (Stylochlamydium venustum); mistakenly grouped with Spongopyle osculosa and Spongotrochus glacialis. 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.

3. Robertson, 1975, includes Spongotrochus (?) glacialis Popofsky, Riedel, 1958, Stylochlamydiumsp. Petrushevskaya, 1967 and Spongodiscus (?) setosus (Dreyer), Petrushevskaya, 1967; "This species loads very heavily in factor 1 (subpolar) and also loads to a lesser degree in factor 2 (subtropical). This species occurs in high abundances throughout the study area but occurs most abundantly in the northernmost part of the northwest Pacific and in the Bering Sea. Low abundances characteristic of the Sea of Okhotsk today extend over the area north of 45 degrees N at 18,000 YBP."