Doryconthidium sp. cf. D. hexactis |
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Is Doryconthidium a cubospherid?
(24/10/2003) |
Benson (1966, p.145-146) states that this species conforms to the definition of the genus Doryconthidium Vinassa de Regny (1898, R. Accad. Lincei, Rend., v. 7, pt. 2, p. 36) in the presence of three concentric shells and a single polar spine. The shells in the Gulf of California tests, however, are joined by six mutually perpendicular radial beams; thus, they conform to the basic structure of cubosphaerid radiolarians. The accessory radial spines as described for this species, in a few tests, do continue inwards as thin, accessory radial beams, but the basic cubosphaerid structure of the six main beams is present. Except for longer accessory radial spines, Renz’s (1974, pl. 14, fig. 9) illustration of Actinommid 3 gen. and sp. indet. appears to be of the same species as the Gulf of California species; the sizes of the cortical shell and polar spine of her specimens are within the limits of those of the Gulf species, but she did not note the presence of the innermost medullary shell nor the presence of six mutually perpendicular radial beams. Caulet’s illustrations of ?(Axoprunum) monostylum Caulet (1986, Initial Repts. DSDP, 90, p. 849, pl. 1, figs. 9-11) appear to be identical with the illustration of the Gulf species, but the diameter of the cortical shell of his species is smaller (80-90 µm vs. 108-135 µm), and he notes six instead of four radial beams in the equatorial plane in addition to the two polar beams. He also records its highest stratigraphic occurrence as lower Pleistocene.
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