S73

Heliodiscus asteriscus Haeckel

Heliodiscus asteriscus Haeckel, 1887, p. 445, pl. 33, fig. 8; Hays, 1965, p. 171, pl. II, fig. 7; Nigrini, 1967, p. 32, pl. 3, figs. 1a, b

DESCRIPTION

"Cortical shell forms a discoidal biconvex lens. Pores circular to subcircular, sometimes hexagonally framed, fairly regularly arranged over most of the smooth shell surface, but irregular in size, shape, and arrangement near the center of the disc; 7 or 8 (sometimes to 10) pores on a radius.

"Medullary shell spherical to ellipsoidal with a diameter approximately 0.3 that of cortical shell. Pores numerous, small, and irregular. Radial beams, 12-16, extend from the medullary shell to the central region of the discoidal surface of the cortical shell. Inner medullary shell delicate, always held eccentrically within outer one by numerous radial beams... Pores large, subcircular, and irregular.

"Radial spines 8-12, well developed, straight, 3-bladed near the disc, becoming cylindrical distally, placed more or less regularly around the margin of the cortical shell. Spines up to 0.5 or .75 cortical shell diameter; rarely forked. Usually a few short slender marginal by-spines present." (from Nigrini, 1967). DIMENSIONS "Diameter of cortical shell 136-191; of outer medullary shell 45-63 microns; of inner medullary shell approximately 9-18 microns." (from Nigrini, 1967).

REMARKS

1. Benson's (1966) description and dimensions of this species (p. 200) are consistent with the above.

Plate 9, figures 1,2

S74

RECENT DISTRIBUTION

1. Hays, 1965, fig. 15; "It has not been observed from core tops south of the Polar Front and is rarely an important constituent of samples from north of it.

"Heliodiscus astericus occurs regularly in the samples from core V-16-66 below 720 cm, indicating a range at least as far back as zone phi. Like Axoprunum stauraxonium, it does not occur in the phi zone from cores taken south of the Polar Front."

2. Benson, 1966; "This species is of cosmopolitan but rare occurrence in the Gulf [of California]. It is ... common (3.0%) only at station 194... In the absence of known upwelling near station 194, it must be concluded that the increase in this species at this station is due to its tolerance of waters with slightly higher than average temperature and salinity... It has a slightly greater abundance in the southern Gulf."

3. Nigrini, 1967, fig. 14; "Indian Ocean occurrences - H. asteriscus is found in both low and middle latitudes, forming 1 percent to 7 percent of the described population. It was present in all counted samples."

4. Nigrini, 1970, fig. 13; belongs to a tropical assemblage derived by recurrent group analysis of North Pacific samples, but the species ranges too far north to be useful in down-core analysis.

5. Lozano, 1974, Fig. IV-7; "Generally present in samples from the Atlantic and practically always found in samples from the Indian Ocean under subtropical waters where it reaches a minimum of 0.7 percent of the total radiolarian fauna.

"The maximum February sea surface temperature under which it is found is 9 degrees C in the Atlantic and 6 degrees C in the Indian Ocean."

6. Molina-Cruz, 1975, Code S14; used in factor analysis of southeast Pacific assemblages; cf. Appendix 10 for percent S14 at each station.

7. Morley, 1977 (Heliodiscus spp.), Fig. I-16; counted together with H. echiniscus; "The present author believes that H. echiniscus is probably a morphological variant of H. astericus...This taxonomic group loads highest in factor 4 (subtropical). At present this group of species is absent in samples south of 46 degrees S. At 18,000 YBP the 0% contour is shifted northward by approximately 2 degrees of latitude to 44 degrees S."