S57

Axoprunum stauraxonium Haeckel

Axoprunum stauraxonium Haeckel, 1887, p. 298, pl. 48, fig. 4; Hays, 1965, p. 170, pl. 1, fig. 3

DESCRIPTION

"Shell ellipsoidal, showing considerable variation in thickness, the thicker individuals having rougher surfaces. Pores evenly spaced, circular to subcircular, in some specimens pores have double edges, pores 4-6 times bar width, 12-18 along major axis, 8-12 across minor axis. Shell bears 2 unequal polar spines, cylindrical to conical, weakly three-bladed at base. Medullary shell thin-walled, subspherical, occasionally double, more commonly single, pores subcircular, 6 across equatorial diameter, shell supported by internal extensions of polar spines plus 6 radial beams lying in or near the equatorial plane. Radial beams thin, but thicken at each end. Often the medullary shell is missing, especially in thin shelled individuals; however, the radial beams are almost always present." (from Hays, 1965).

"Heavy shelled specimens sometimes are similar to Druppatractus acquilonaris but A. stauraxonium is smaller in size (>165 microns along the major axis" (from Robertson, 1975).

DIMENSIONS "Length of major axis 145-165, of minor axis 125-145, of long polar spine 55-80, of short spine 40-60. Diameter of medullary shell 30-45." (from Hays, 1965).

REMARKS

1. According to Petrushevskaya (1975, p. 570) this genus may be distinguished from Stylosphaera by the position of the rods joining the medullary and cortical shells. In Axoprunum, except for the polar spines, they all lie approximately in the equatorial plane. It differs from the genus Stylatractus (which Petrushevskaya, 1975, synonymized with Amphisphaera) by having polar spines longer than the major axis of the cortical shell. This latter distinction is questionable since the polar spines of the type species (cf Haeckel, 1887, p. 48, fig. 4) are shorter than the major axis of the cortical shell.

Plate7, figures 2, 3

S58

RECENT DISTRIBUTION

1. Hays, 1965 (Fig. 13); "A. stauraxonium is one of the most abundant and widespread of those species found in the tops of cores north of the South Polar Front. Its presence in the lower part of V-16-66 (zone phi) indicates that it extends back in time at least as far as the time represented by this zone. It does not occur, however, in the other cores containing the red clay fauna; thus it seems that in the past, as today, it was excluded from the colder southern waters of the area."

2. Molina-Cruz, 1975, Code S50; counted together with Stylosphaera lithatractus Haeckel and used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S50 at each station.

3. Robertson, 1975; "This species loads in factor 2 (subtropical). At the present its occurrence is limited to the region southeast of a line running from 35 degrees N, 145 degrees E to 50 degrees N, 180 degrees. At 18,000 YBP it is absent north of 38 degrees N, except for a small occurrence in V20-119 which may be an incorrect identification."

4. Morely, 1977 (Axoprunum spp.), Fig. I-11; "The description of this species given by Haeckel (1877) is followed. Haeckel did not include a spherical medullary shell in this original description. Although this species is probably identical to A. stauraxonium, it is referred to in this study as Axoprunum spp. This species loads highest in factor 4 (subtropical). At present this species is absent in almost all samples south of 40 degrees S. Because of the absence of samples in the subtropical region at 18,000 YPB, it is difficult to ascertain variations in distribution of this species at this level."