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Hexacontium sp. cf. H. gigantheum det. Benson, 2003

Description - Add description

Benson, 1966, p. 149-153; pl.3, figs.13-14, pl. 4, figs. 1-3:

Hexacontium entacanthum [sic.] Jørgensen

Hexacontium entacanthum [sic.] Jørgensen, 1900, Bergens Mus. Aarbog (1899), p. 52, Pl. 2, fig. 14, Pl. 4, fig. 20; 1905, Bergens Mus. Skrifter, p. 115, Pl. 8, fig. 30.
Hexacontium pachydermum Jørgensen, 1900, Bergens Mus. Aarbog (1899), p. 53; 1905, Bergens Mus. Skrifter, pp. 115-116, Pl. 8, fig. 31.

Cortical shell generally spherical but varies from subspherical to suboctahedral and in a few specimens has a subquadrate outline; surface ranges from completely smooth to generally one with thorns or thin conical by-spines which arise at the nodes of intervening bars as well as along the bars; in one specimen the by-spines branch and anastomose distally at a common distance from the cortical shell to form a secondary outer shell; pores subcircular or subelliptical, subpolygonal, or in a few tests with irregular shapes, subequal in size in most tests but in a few with unequal size, with subregular (hexagonal) to irregular arrangement, with or without polygonal frames, in most specimens 8-9 on the half circumference but ranging from 7-13. Second shell spherical to subspherical, thin-walled, with surface ranging from smooth to one with scattered thorns or thin conical spines which in a few specimens join with the cortical shell to form thin secondary beams; pores subpolygonal to polygonal, unequal to subequal in size, with irregular to subregular arrangement, generally 6-8 on the half circumference but ranging from 5-10. First shell thin-walled, subspherical to suboctahedral, with 2-3 relatively large polygonal pores on the half-circumference. Each of the six mutually perpendicular radial beams arise from the corners of the suboctahedral inner shell, remain thin and cylindrical until they pierce the second shell after which they are relatively heavy and three-bladed in section. Beams continue beyond cortical shell as relatively heavy and in several specimens very long three-bladed spines, all six nearly of equal length and breadth. In several specimens not all beams and spines are mutually perpendicular; some specimens have seven or eight beams, the extra beams representing either bifurcations of one or more of the six primary beams at the level of either the first or second shell or separate beams arising from the first shell and with no regular relationship to the six primary beams; a few specimens observed with only five of the six primary beams present.

Measurements; based on 101 specimens from station 81: diameter of cortical shell 74-154 µm, of second shell 30-50 µm, of first shell 12-22 µm; average length of main spines per specimen 9-112 µm.

Remarks. In number of shells, their size, and the nature of their pores, the Gulf species is identical with both Hexacontium entacanthum [sic.] Jørgensen and H. pachydermum Jørgensen. The most important reason for identification of the Gulf species with these species is the presence in them of a polyhedral inner or first shell with relatively large polygonal pores. H. pachydermum and H. entacanthum [sic.] differ only in that the cortical shell of the latter is smooth and that of the former has by-spines and a thicker wall. Both types of tests were observed from the Gulf with no significant differences in size and structure; thus, Jørgensen's species were placed in synonymy, the name H. entacanthum [sic.] being the nominal species because of page preference over the other. Jørgensen (1905, p. 115) admits the possibility that these two species are identical. Certain of Haeckel's species which conform in size and in the nature of the cortical shell pores to the Gulf species but differ in the presence of an inner spherical instead of polyhedral shell having numerous circular pores include H. octahedrum Haeckel (1887, p. 193), H. favosum Haeckel (1887, p. 194, Pl. 24, figs. 2, 2a), H. sceptrum Haeckel (1887, pp. 194-195, Pl. 24, figs. 1, la), H. asteracanthion Haeckel (1887, P. 196) [= Haliomma asteracanthion Haeckel, 1861a, p. 816, Actinomma asteracanthion Haeckel, 1862, p. 441, Pl. 23, figs. 5, 6], and possibly H. axophaenum Haeckel (1887, pp. 196-197), H. polygonale Haeckel (1887, p. 197), H. antarcticum Haeckel (1887, P. 197; Popofsky, 1909, pp. 210-211), and H. setosum Haeckel (1887, p. 198). Hexacromyum elegans Haeckel (1887, p. 201, Pl. 24, fig. 9; Popofsky, 1912, pp. 92-93, text figs. 5-7) was previously discussed in the remarks under Hexacontium. Species of the two-shelled cubosphaerid genus Hexalonche Haeckel that apparently lack the inner shell but conform to the Gulf species in size and nature of the cortical shell pores include Hexalonche octahedra Haeckel (1887, p. 181, Pl. 22, figs. 8, 8a), H. anaximandri Haeckel (1887, p. 182, Pl. 22, fig. 5), H. aristarchi Haeckel (1887, p. 185, Pl. 22, fig. 3; Popofsky, 1913b, pp. 87-88, text fig. 2), and H. philosophica Haeckel (1887, p.186, Pl. 22, fig. 4).
Study of Haeckel's type material should verify the above relationships between the species of this group. In all the above-mentioned species that were illustrated, none of them appeared to be significantly different from the Gulf species other than the differences already discussed

Distribution. This species is present at all stations in the Gulf except 214. It is one of the most abundant spumelline species found in the Gulf sediments. It occurs with maximum frequency at stations 206, 194, and 184 (17.4%, 12.6%, and 11.0% respectively), where it is abundant. It is common at all other stations except at 34, 46, 56, and 203 where it is rare. Its distribution pattern in the northernmost part of the Gulf (particularly stations 206, 194, and 184) is parallel to that of Diploplegma banzare Riedel; therefore, it is able to inhabit water masses of slightly higher than average salinity and temperature.
Between stations 90 and 99 across the Gulf it has a slightly greater frequency at stations 91, 92, and 99, but is common at the others. This represents an increase in its frequency in the areas of upwelling on both the east and west sides of the Gulf. Its rare or nearly rare occurrence in the southern Gulf and its general increase northward indicates that it is a normal member of the tropical Pacific oceanic fauna and that it inhabits water masses with slightly higher salinty and temperature.
This species is apparently cosmopolitan at all latitudes. Jørgensen (1900, pp. 52-53; 1905, pp. 115-116) states that it is fairly abundant in deeper water layers (300 meters) off the northwest coast of Norway and in Norwegian fjords and that it is a temperate oceanic form. It apparently inhabits warmer, deeper waters in this region. Most of the species mentioned in the remarks above were reported from all oceans but generally from tropical or subtropical regions, although a few were reported from high latitudes (Hexacontium antarcticum Haeckel and Hexalonche philosophica Haeckel, the former from the Antarctic, the latter from the North Atlantic near Iceland).

Benson 1966











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