S55

Stylatractus spp.

? Stylatractus neptunus Haeckel, 1887, p. 328, pl. 17, fig. 6; Riedel, 1958, p. 226, pl. 1, fig. 9

? Stylatractus sp. Petrushevskaya, 1967, p. 27, fig. 15, I-IV.

DESCRIPTION "Shell ellipsoidal, consisting of three concentric lattice shells and two unequal polar spines. Innermost shell spherical or subspherical, thin-walled, with numerous circular or subcircular pores, joined to the second shell by few radial beams. Second lattice-shell somewhat ellipsoidal, usually thick-walled, with large subcircular or angular pores, joined to the outermost lattice-shell by numerous radial beams. Outermost lattice shell ellipsoidal, thick-walled, thorny, with irregular pores (7-16 on a half-equator) which are large when a few in number, and are in many specimens subdivided by centripetal ingrowths from the pore-walls to form numerous smaller pores. Polar spines heavy, usually cylindro-conical and fluted at the base, rarely weakly three-bladed." (from Riedel, 1958).

DIMENSIONS Based on 21 specimens. "Major diameter of outermost lattice-shell 130-150 microns, its minor diameter 115-140 microns. Major diameter of second lattice-shell 75-85 microns, of innermost lattice-shell 30-40 microns. Length of longer polar spine 55-95 microns, of shorter polar spine 30-75 microns." (from Riedel, 1958).

"Eleven specimens from about 25 degrees N in the Eastern Pacific were found to be generally smaller than those measured by Riedel in the Antarctic." (Gail Lombari, personal communication).

REMARKS 1. Benson (1966) described 2 similar species, i.e., Xiphatractus cronos (Haeckel) and Xiphatractus pluto (= S. neptunus Haeckel according to Benson): X. cronos "differs from [X. pluto] in the thinner wall of the cortical shell (3-5 microns), the lack of small, circular, secondary pores filling the spaces of the larger pores of the cortical shell, and in generally less robust polar spines."

2. "The North Pacific form is robust, with markedly elliptical cortical shells. "Rosettes" occasionally developed in cortical shell pores. Polar spines almost always coaxial....A second form marked by a smaller, lighter, cortical shell with large open pores and polar spines considerably

S56

longer S56 than the cortical shell diameter is also present, but is not included with this species. It is considerably less abundant." (from Sachs, 1973).

3. According to Molina-Cruz (1975) "this species group is distinguished from Stylosphaera lithatractus by its generally smaller size and strongly bladed polar spines."

4. "The internal characteristics and variations in spine dimensions in the species which compose this group vary widely." (from Morley, 1977).

RECENT DISTRIBUTION

1. Riedel, 1959; "Specimens closely resembling those from the Antarctic have been found in the northern Pacific, and in the tropical parts of the Pacific and Indian oceans....it may thus be a cosmopolitan species."

2. Sachs, 1973, Code 13S; "Widely distributed, to 5% of fauna, and concentrated in Polar (Northermost) and bottom-influenced factors."

3. Molina-Cruz, 1975, Code S51; used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S51 at each station.

4. Robertson, 1975; "The shape of the spines and degree to which the internal structure of these forms could be distinguished is highly variable.... This species loads most heavily in factor 1 (subpolar). Its greatest abundances both at the present and 18,000 YBP are found north of about 45 degrees N. There is evidence for a slight southern shift of the zone of highest abundance from the present to 18,000 YBP."

5. Morley, 1977, fig. I-15; "This group of species loads highest in factor 4 (subtropical). This species has a general cosmopolitan distribution at present and 18,000 YBP. No major changes in distribution pattern appear to occur between today and 18,000 YBP."