radiolaria - rads_cat - Stylosphaera megaxyphos megaxyphos

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Stylosphaera megaxyphos megaxyphos

Citation: Stylosphaera megaxyphos megaxyphos Clark & Campbell 1942

Type specimens: pl.5, figs.5,6,14; pl.6, fig.6

Type repository: University of California, Museum of Paleontology, San Francisco

Family (traditional): Actinommidae

Family (modern): Rhizosphaeridae

Shell globular, with two greatly elongate polar spines more than ten times their basal diameter in length, subequal, angled, with the faces of the angles concave; cortical shell spherical, rather thick-walled, rather with subuniformly subcircular pores, five or six across a radius, sunken into hexagonal areas, with sepaloid projections; medullary shell, with three or four pores across a radius, and very thin bars, beams heavier, six visible in one plane.

Length of polar spines, 210-290µm; diameter of cortical sphere, 150-160µm; of medullary sphere, 44-76µm; of pores, 13.2-19.8µm.

Distinguishing characters: There is some variation in the length of the polar spines in different individuals and, also, in some specimens between the polar spines of the two axes. In some individuals the spines are slightly asymmetrical.
A broken specimen in which the polar spines are missing is illustrated in figure 5 of Plate 5. This individual measures 150 by 160µm, with the medullary shell 51µm, and the pores 21µm. The polar spines of this specimen are snapped off at the base and do not show well in the photograph due to its orientation. That they were formerly present is evident only upon careful focus with the microscope. Such broken individuals may be confused with more or- less globular species, as, for example, Carposphaera buxiformis n. sp., or others.
Figure 14 of Plate 5 shows an isolated central sphere with one of the polar spines and a few of the beams. The specimen is obviously defective and broken, and the polar spine thinner than in the usual specimens; however, in length and general dimensions and other characters, this specimen agrees best with similar parts of other specimens and is assigned to S. megaxyphos megaxyphos n. subsp., or others.
Another one of our figures (Pl. 5, fig. 6) is of a small form, the polar spines being 150µm in length, the cortical shell similar in diameter, the medullary shell 40.8µm, the wall with a thickness of 8.8µm, and the pores having a diameter of 10µm. Polar spines are an obviously adaptive response to life in the sea and to the orientation of the shell which possesses them. They have been independently developed in several sub-orders of the Spumellaria and tend to multiply strongly in some species.
Stylosphaera megaxyphos megaxyphos n. subp. has a single pair of opposite polar spines unlike the other subspecies in which there are three, four, or even five polar spines.

The authors here list this subspecies under the subgeneric name Stylosphaerantha and include the subgeneric name in the species name.

CATALOG OF ORIGINAL DESCRIPTIONS: Stylosphaera megaxyphos megaxyphos Clark & Campbell 1942

Stylosphaera megaxyphos megaxyphos

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