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Actinosphaera acanthophora (Popofsky, 1912)

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Benson, 1966, p. 127-131; pl. 2, figs. 8-10:

Carposphaera acanthophora (Popofsky)

Haliomma acanthophora Popofsky, 1912, Deutsche Sudpolar-Exped., vol. 13, pp. 101-102., text fig. 13.
?Cenosphaera cristata Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 66.
Cenosphaera cristata Haeckel?, Riedel, 1958, B.A.N.Z.A.R.E. Repts., Ser. B, vol. 6, pt. 10, p. 223, Pl. 1, figs. 1, 2.

Majority of tests consist of a single, large, spherical shell, but several were observed with a small, polyhedral, thin-walled inner or medullary shell. Surface of cortical shell of most specimens rough with numerous thorns or conical to three-bladed spines which arise from the nodes of the intervening bars as well as from the bars; in a few specimens, particularly those with smaller pores and thin intervening bars, surface relatively smooth with only a few scattered thorns or spines; the few spines that continue inward as thin radial beams to the medullary shell are not different from the other spines of the cortical shell. Wall of cortical shell of variable thickness but in most specimens relatively thick. Pores of cortical shell of all shapes and sizes, unequal, with irregular arrangement, 9-20 on half the circumference; intervening bars in most tests heavy, in a few tests thin, separating smaller pores; polygonal frames if present not well-developed, absent particularly in specimens with small pores and thin intervening bars. In many of the specimens lacking a medullary shell there are thin, internal, centripetal spines that arise from the inner surface of the cortical shell and continue outside the shell as short thorns or spines. Medullary shell polyhedral in shape with large unequal polygonal pores separated by thin intervening bars, 2-3 pores on half the circumference. Medullary shell joined to cortical shell by 10-20 thin, delicate, radial beams that arise from its surface, but which in tests lacking this shell are represented by the centripetal spines arising from the inner surface of the cortical shell. In many tests the medullary shell is nearly invisible because of its thin, delicate meshwork; in other tests it was broken away from the radial beams.

Measurements; based on 30 specimens from stations 27 and 71: diameter of cortical shell 151-276 µm, of medullary shell 31-37 µm (3 specimens).

Remarks. The presence of the medullary shell and the lack of distinct radial main spines on the surface of the cortical shell conform to the definition of the genus Cenosphaera Haeckel (1882, p. 451). Other than secondary surface spines or thorns as in the Gulf specimens, Popofsky's illustration of Haliomma acanthophora Popofsky (1912, text fig. 13, P. 101) does not show distinct radial main spines arising from the surface of the cortical shell; therefore, it does not belong in Haliomma Ehrenberg. Except for a spherical instead of polyhedral medullary shell, Popofsky's illustration shows no other differences from the Gulf specimens of this species. Riedel (1958, p. 223) tentatively identified spherical single shells from Antarctic sediments as Cenosphaera cristata Haeckel. His description and illustration of this species does not differ from that of the cortical shell of the Gulf specimens. The presence of the inner medullary shell is rarely observed and in many tests when present is barely visible. Its presence or absence is subject to intraspecific variation, but because it is present in fully developed forms the species has been placed in the genus Carposphaera Haeckel.
Riedel (op. cit.) states that the Antarctic species resembles to some extent Cenosphaera favosa Haeckel (1887, p. 62, pl. 12, fig. 10) and C. globosa Popofsky (1909, p. 207, Pl. 22, fig. 2) both of which have regular equal pores. A few large specimens from the Gulf have small but irregular, unequal pores separated by thin intervening bars. Other species that resemble the Gulf species but differ in the presence of thinner bars separating large irregular pores include Haliomma capillaceum Haeckel (1862, p. 426, Pl. 23, fig. 2) and H. erinaceum Haeckel (1862, p. 427, Pl 23, figs. 3, 4; Popofsky, 1912, p. 102, Pl. 4, fig. 1). Study of the type material of these species may result in their placement in synonymy with Carposphaera acanthophora. In both, the spines continuous inward with radial beams are not distinctly different from the secondary spines on the surface of the cortical shell. The polyhedral medullary shell and thin delicate radial beams are the same as in the Gulf specimens.

Distribution. This species has a somewhat complex distribution pattern in the Gulf. It occurs at all stations except 203, 208, and 214 in the radiolarian-poor area of the northernmost part of the Gulf. It is abundant at only one station, namely, the near shore station 90, where it is the second most abundant species (11.4%). It is common at stations 95 and 184 (4.0% and 2.0%, respectively) and rare at all others. If its distribution in only the axial portion of the Gulf is considered, it is rare in the southern Gulf, increases to a maximum in the central Gulf, and decreases northward but undergoes a slight increase at stations 184, 191, 192, and 194. The latter increase may be in part a function of fewer species present in this region but also may be a result of this species having a greater tolerance for higher than average temperature and salinity as apparently has Diploplema banzare Riedel. Its maximum frequency in the central Gulf may be the result of upwelling in this region, but its distribution across the Gulf from stations 90 to 99 is complex. Its relative frequencies at stations 90, 91, 92, 93, 95, and 99 are 11.4%, 1.8%, 1.8%, 0.0%, 4.0%, and 0.4%, respectively. Station 90 is near the western shore of the Gulf, and it along with stations 91 and 92 are located in regions of upwelling. It is very rare at station 93 but immediately east of this station its percentage increases to 4.0%, its second highest frequency in the Gulf stations sampled. Its very high frequency at station 90 may be explained by either the reduction in total number of species at this station or its response to upwelling, or both. The relatively high frequency of this species at station 95 may be the result of lateral transport along the bottom from the western margin of the Gulf.
Riedel (1958, p. 223) states that members of this species or species-group have been reported from both high and low latitudes. Final analysis of its world-wide distribution is dependent upon further taxonomic study of this group in order to determine the relationships between the various species if actually they are not the same species. It appears, however, that this species is cosmopolitan.

Benson 1966











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