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Hexacontium sp. cf. H. heracliti Benson, 1966

Description - Add description

Benson, 1966, p. 158-160; pl. 4, figs. 8-10:

Hexacontium cf. hericliti [sic.] (Haeckel)

?Hexalonche heracliti Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 187, Pl. 22, fig. 7.

Cortical shell spherical, thick-walled, with rough surface, in all specimens with cluster of 2-6 or more thin, conical by-spines at nearly all nodes of the intervening bars; in a few specimens the by-spines have distal branches that anastomose at a common distance from the cortical shell to form an irregular secondary outer shell or portions thereof; pores of unequal size, relatively large, two to ten times as broad as the bars, subpolygonal to elliptical or subcircular, without polygonal frames, with irregular arrangement, 6-8 on the half circumference; around base of each main spine are three, smaller, equal, circular pores, each located between the blades of the three-bladed spine. Second shell subspherical to globular, with surface ranging from relatively smooth to one with scattered thorns or thin conical spines, with polygonal to subcircular, subequal, subregularly arranged pores separated by thin intervening bars, 7-10 pores on the half-circumference. First shell subspherical to polyhedral, with 3-4 large polygonal pores on its half-circumference. Six, rarely 7 or 5, in nearly all specimens mutually perpendicular, radial beams arise from the surface of the first shell, become heavy and three-bladed after piercing the second shell, trifurcate before joining the cortical shell as in H. cf. heteracantha [=Hexacontium arachnoidale], and continue beyond cortical shell as relatively heavy, three-bladed to conical spines of equal length. In specimens with very thick-walled cortical shells the main spines are generally very short, stout, and conical; in all specimens the spines are short relative to the diameter of the cortical shell (up to only 2/5 the diameter of the cortical shell).

Measurements; based on 30 specimens from stations 27. 34, 46, 56, 60, 71, and 81: thickness of cortical shell wall 9-18 µm; diameter of cortical shell 145-203 µm; of second shell 47-53 µm, of first shell 18-25 µm; length of main spines 21-65 µm.

Remarks. The differences between this species and H. cf. heteracantha [=Hexacontium arachnoidale] were discussed under the remarks of the latter. It differs from Hexalonche heracliti Haeckel in the lack of the innermost shell, a feature Haeckel may have overlooked. Haeckel did not mention the trifurcation of the radial beams before they join with the cortical shell; nor did he mention the three smaller circular pores of the cortical shell around the base of each radial spine. The clusters of thin, conical by-spines at the nodes of the intervening bars of this species are present in all specimens observed from the Gulf, and due to the constancy of this character a separate species was defined. Actually H. cf. heracliti may be a subspecies with its counterpart being H. cf. heteracantha (Popofsky)[=Hexacontium arachnoidale], but there are no significant geographic differences in the distribution of these two forms; they could be isolated, however, by inhabiting different water layers in the water column at any particular locality.

Distribution. This species is rare at all stations where it is present and is absent at stations 64, 115, 130, 133. 151, 184, 191, 194, and all those to the north. It undergoes no significant changes in its frequency throughout the Gulf; therefore, it is probably an oceanic form.
Haeckel (1887, p. 187) reported Hexalonche heracliti from the surface of the Indian Ocean near Madagascar and Rabbe. If this is the same as the Gulf species, it is apparently cosmopolitan in the tropical parts of the world's oceans. It has not been reported from high latitudes.

Benson 1966











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