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|Shell conical-campanulate, of moderately heavy structure, consisting of two, three or four segments. Cephalis subglobose, with small, sparse pores, and bearing two short, acicular spines - one vertical, approximately apical, and the other lateral, oblique. Collar stricture slight. Subsequent part of shell, comprising its main bulk, will be termed the thorax, though in some specimens it appears to be divided by an ill-defined internal transverse ridge into an upper and a lower portion. Thorax approximately conical, in many specimens flared at a wider angle distally than proximally. Thoracic pores subcircular proximally, becoming polygonal distally, arranged in usually 4-7 transverse rows which are indefinite in some specimens. In most specimens, three short, downwardly directed acicular spines penetrate the thoracic wall near its junction with the cephalis. In many specimens a further shell-segment is present marked off from the thorax by an internal septal ring. When present, this abdomen is short, truncate-conical, usually flared at a wider angle than the thorax, with usually 2-4 transverse rows of polygonal pores separated by more delicate bars than those of the thorax. |
|Benson, 1966, p. 441-444; pl. 29, figs. 14-16:|
Theocalyptra davisiana (Ehrenberg)
Cycladophora? davisiana Ehrenberg, 1862, Akad. Berlin, Monatsb. (1861), p. 297; 1873b, Akad. Berlin, Abhandl. (1872), Pl. 2, fig. 11.
Pterocodon davisianus Ehrenberg, 1862, Akad. Berlin, Monatsb. (1861), pp. 300-301; 1873b, Akad. Berlin, Abhandl. (1872), Pl. 2, fig. 10.
Eucyrtidium davisianum (Ehrenberg), Haeckel, 1862, Die Radiolarien, pp. 328-329.
Pterocanium davisianum (Ehrenberg), Haeckel, 1862, Die Radiolarien, p. 332.
Stichopilium davisianum (Ehrenberg), Haeckel, 1887, Challenger Rept., Zool., vol. 18, pp. 1437-1438.
Theocalyptra davisiana (Ehrenberg), Riedel, 1958, B.A.N.Z.A.R.E. Repts., ser. B, vol. 6, pt. 10, p. 239, Pl. 4, figs. 2, 3, text-fig. 10.
Remarks. The writer agrees with Riedel's (1958, p. 239) reasons for assignment of this species to the genus Theocalyptra. Specimens from the Gulf do not differ from Riedel's description of the species. A few tests resemble Theocalyptra bicornis (Popofsky) Riedel (op. cit,. p. 240, Pl. 4, fig. 4) in shell outline but are assigned to T. davisiana.
The presence of an internal septal ring dividing the abdomen from the thorax was observed only rarely in Gulf specimens. The third joint or abdomen is not well-developed in most specimens. The characteristic features of this species are the relatively smooth cephalis separated by only a slight stricture from a slender conical thorax which flares widely and abruptly changes contour distally to form a distinct shoulder in most tests and a less widely flaring joint (?) below the shoulder and of variable degree of development, being long in only a few specimens. The thoracic pores are arranged in transverse rows, increase in size distally, and are generally subcircular to subpolygonal. The apical and vertical spines are generally present but are thin and conical, rarely three-bladed; the primary lateral and dorsal spines generally originate at or near the collar stricture, but in a few specimens are very short thoracic ribs; the spines in a few tests are joined by lattice to the thoracic wall, presenting the appearance of low wings; no secondary lateral bars or spines were observed; four collar pores are present.
Except for the absence of a pronounced angular change of contour on the thorax, forms illustrated by Bailey (1856, Pl. 1, figs. 13, 14) and assigned to Halicalyptra? cornuta Bailey are similar to the Gulf forms. Bailey's type material was not examined; therefore, placement of his species in synonymy with the Gulf species must await further study.
Measurements; based on 30 specimens from stations 27 and 34: maximum length of test 63-107 µm; length of cephalis 15-21 µm, of thorax (including "joint" below shoulder) 37-73 µm; breadth of cephalis 16-25 µm; maximum breadth of test (joint below shoulder) 62-102 µm, of thorax 62-102 µm; length of apical spine 1-18 µm, of vertical, spine 0-16 mm, of dorsal and primary lateral spines 2-10 µm.
Distribution. This species is cosmopolitan in the Gulf but has a much greater frequency in the southern half of the Gulf. It is absent at stations 64, 71, 90, 130, 184, 191, and all those north of 194. Its frequency is greater at stations located within the axial portion of the Gulf. This together with its general absence at marginal stations indicates its preference for more nearly oceanic, offshore waters. It is common at most of the stations in the southern Gulf, namely, at stations 27 (4.6%) where it is the fourth most abundant species, 34 (2.2%), 46 (2.6%), 56 (2.2%), 60 (2.8%) where it is the sixth most abundant species, and 81 (2.8%). It is nearly common at stations 95, 115, and 136. Its decrease northward in the Gulf indicates its greater affinity for oceanic waters than for Gulf waters. It apparently does not respond to upwelling.
Riedel (1958, p. 239) states that this species occurs in the American and Indian Ocean sectors of Antarctic waters and in the tropical parts of the Pacific and Indian Oceans. Ehrenberg (1862, pp. 297, 301) first reported this species from the northern Atlantic. Riedel (op.cit.) states that this species may be cosmopolitan, and it appears to be more common in sediments from high and middle latitudes than in those from tropical regions.
|Skeleton conical, thick-walled, consisting of four segments. First segment, "cephalis", with rather small round pores; bearing two small horns formed from needles A and Vert. Walls of first segment passing smoothly into walls of second. Second segment, "thorax", small with randomly scattered pores approximately as small as those of first segment. Walls of "thorax" pierced by needles D, Lr and L1, which form slender lateral processes to shell (often broken off). Second segment usually separate from third by distinct constriction; internal thickening or bulge distinguishable on their boundary. Third segment far wider than second, with 3-4 transverse rows of 11-13 pores each; in second and third rows are largest pores of shell. Third segment ending in fairly thick internal bulge. Fourth segment still wider than third. We had specimens in which 3-4 uneven transverse rows of pores could be counted, but there was not one shell with a closed fourth segment (although hundreds of specimens were examined). Internal skeleton composed of all basic elements (MB, D, Lr and L1, A and Vert), but they are very slender and partially fused to walls of shell. |
Dimensions: length of first segment about 20 micrometer, width 20-22 micrometer, length of second segment about 30 micrometer, width 35-45 micrometer, length of third segment 40-50 micrometer, width 70-85 micrometer, length of fourth segment up to 40 micrometer and more, width 100-130 micrometer.