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Anthocyrtidium zanguebaricum (Ehrenberg, 1872)

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Benson, 1966, p. 468-472; pl. 32, figs. 3-5:

Anthocyrtium oxycephalis (Haeckel)

Sethocyrtis oxycephalis Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1299, Pl. 62, fig. 9.
Not Sethocyrtis oxycephalis Haeckel, (as Anthocyrtidium cineraria H.) Riedel, 1957, Swed. Deep-Sea Exped., Repts., vol. 6, fasc. 3, p. 84.
?Anthocyrtis zanguebarica Ebrenberg, 1872a, Akad. Berlin, Monatsb. (1872), p. 301; 1872b, Akad. Berlin, Abhandl. (1872), p. 285, pl. 9, fig. 12.
?Anthocyrtis ovata Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1272, Pl. 62, fig. 13.
?Anthocyrtium zanguebaricum (Ehrenberg) Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1277.

Cephalis elongate, cylindrical, with a straight dorsal face that merges upward with a heavy, three-bladed apical horn that is about the same length as the cephalis. The apical bar is present as a rib in the dorsal face of the cephalis and extends upward as the dorsally projecting blade of the three-bladed apical horn. A pair of conspicuous dorso-lateral lobes present at the base of the cephalis, separated by distinct constrictions coincident with ribs in the cephalic wall that correspond to the lower part of the apical bar and the left and right apical-lateral arches; base of lobes separated from thorax by a constriction coincident with ribs that correspond to the dorso-lateral portion of the collar ring. Ventro-lateral portion of cephalis separated from thorax by a constriction coincident with a rib corresponding to the ventral arch of the collar ring (these relationships illustrated by Riedel, 1957, p. 86, fig. 4). Pores of cephalis equal in size, circular, with hexagonal arrangement. In many specimens the cephalis open at the top. The two lateral blades of the three-bladed apical horn are latticed proximally and merge with the lateral faces of the cephalis. Vertical spine not observed, inconspicuous if present. Four collar pores present separated by the primary lateral, vertical, and median bars; in many specimens the primary lateral and dorsal bars extend as ribs in the thoracic wall and terminate in short spines or thorns which arise at the level where the thorax undergoes a distinct change in contour, below the cephalic stricture. Outline of thorax generally trapezoidal, in a few specimens conical or inflated; a distinct, often angular change in contour proximally and a definite inward curvature distally; thorax terminates distally in most specimens in a short, hyaline peristome surrounding the constricted circular mouth. Pores of thorax hexagonally arranged in vertical rows, subpolygonal to subcircular, increasing gradually in size distally; pores of proximal portion of thorax approximately the same size as those of the cephalis. Surface of thorax smooth, without hexagonal frames surrounding the pores. Subterminal spines lacking in all tests. Peristome with 4 to 14 triangular, flat, tooth-like spines or thorns that converge inward. A few specimens observed without hyaline peristome and associated spines.

Measurements; based on 30 specimens from stations 27 and 34: length of test (including apical horn) 105-194 µm, of apical horn 12-39 µm, of cephalis (top of ventral face to median bar) 30-41 µm, of thorax 62-125 µm; breadth of cephalis 22-42 µm, of thorax 68-105 µm (mean, 89.5 µm); length of peristomal spines 1-15 µm.

Remarks. This species differs from Anthocyrtidium cineraria Haeckel in the complete absence of subterminal spines, in a thorax that is more nearly trapezoidal in outline and less often conical or inflated, and in a mouth of smaller diameter. Both species as well. as Lamprocyclas maritalis Haeckel are very similar in the details of the cephalis as described above. L. maritalis differs from the other two species in the presence of a truncate-conical abdomen separated from the thorax by an internal septal ring. In all of these species as well as several discussed by Riedel (1957, pp. 83-84) the similar cephalic structure appears to indicate a closer relationship than the presence or absence of subterminal spines or the number of post-cephalic joints. All these forms may be combined under a single genus if topotypic material were available for study.
Among the species illustrated in the literature the one most closely resembling the Gulf species is Sethocyrtis oxycephalis Haeckel. Haeckel (1887, p. 1299) placed it in the genus Sethocyrtis because the single specimen he studied lacked a peristome with associated tooth-like spines. However, several specimens from the Gulf were observed with peristome either lacking or rudimentary; therefore, this character is subject to intraspecific variation. Haeckel’s illustration of S. oxycephalis (op. cit., Pl. 62, fig. 9) shows a cylindrica1 cephalis with a heavy, three-bladed apical horn and a thorax with trapezoidal outline, smooth surface, constricted mouth, and no subterminal spines. Riedel (1957, p . 85) placed S. oxycephalis in synonymy with Anthocyrtidium cineraria Haeckel on the grounds that the state of development of both the subterminal and peristomal spines varies among individuals of the species, and occasional specimens are found with no spines; apparently Haeckel based his description of S. oxycephalis on the latter. The result of study of numerous individuals of both species from the Gulf show that indeed the state of development of the terminal and subterminal spines is variable in A. cineraria, but Anthocyrtium oxycephalis can be distinguished from A. cineraria by the features of its thorax including a lesser maximum breadth. In the few specimens with neither a peristome nor subterminal spines, the two species could be distinguished.
Anthocyrtium oxycephalis is also similar to Anthocyris ovata Haeckel and Anthocyrtium zanguebaricum (Ehrenberg). The former is described as having a conical apical horn, and its illustration shows the presence of nine, large, triangular terminal spines which converge inward. Whether or not it represents an intraspecific variation of A.oxycephalis cannot be determined until Haeckel's type material can be studied. Riedel (1957, p. 84) states that he examined the original sediment material from the type locality (“Challenger” station 272) of Anthocyrtis ovata but found no specimens agreeing with Haeckel’s description of this species. Anthocyrtium zanguebaricum (Ehrenberg) apparently has less regular thoracic pores than A. oxycephalis, but this appearance may be the result of Ehrenberg's poor illustration.
The Gulf species is very similar to Anthocyrtium ehrenbergii ehrenbergii (Stöhr) described by Riedel (1957, pp. 83-84) except that no specimens from the Gulf were observed with subterminal spines. In details of the thorax the form described by Riedel is more like Anthocyrtidium cineraria. In fact, Riedel (op cit., p.84) states that it is absent in Quaternary deep-sea sediments and that it may be restricted to the upper Tertiary.

Distribution. In the Gulf this species occurs uniformly but rarely as far north as station 192. It is absent at the marginal station 130 and at station 194 and those north of it with the exception of station 214 where only two radiolarian specimens were found. It is common (2.2%) only at station 56 which is a marginal station located in a region of upwelling. In general it occurs more frequently in the southern half of the Gulf. Its distribution in part may be influenced by upwelling because it does not decrease significantly at stations 99 and 64 which are located in regions of upwelling, although it is very rare at stations 90, 91, and 136, also located in such regions. It is probably an oceanic species which is somewhat influenced by local conditions of upwelling in the Gulf.
Sethocyrtis oxycephalis Haeckel was reported from the tropical part of the central Pacific at "Challenger" stations 263 to 274 (Haeckel, l887, p. 1299). Anthocyrtis ovata Haeckel also was reported from this region. (op. cit., p. 1272). Anthocyrtium zanguebaricum (Ehrenberg) was reported from the Indian Ocean near Zanzibar. In the absence of additional knowledge of its world-wide distribution A. oxycephalis appears to be confined to the tropical parts of at least the Pacific and Indian Oceans.
Benson 1966


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