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Pterocorys minythorax (Nigrini, 1968)

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Benson, 1966, p. 482-485; pl. 33, fig. 5 (not fig. 4):

Theoconus zancleus (Müller) Haeckel

Eucyrtidium zanclaeum Müller, 1859, Akad. Berlin, Abhandl. (1858), pp. 41-42, Pl. 6, figs. 1-3; Haeckel, 1862, Die Radiolarien, p. 321.
Eucyrtidium cranoides Haeckel, 1861b, Akad. Berlin, Monatsb. (1860), p. 838; 1862, Die Radiolarien, pp. 320-321, Pl. 7, figs. 1-3.
Eucyrtidium zanguebaricum Ehrenberg, 1873a, Akad. Berlin, Monatsb. (1872), pp. 312-313; 1873b, Akad. Berlin, Abhandl. (1872), Pl. 9, fig. 22.
Pterocanium sabae Ehrenberg, 1873a, Akad. Berlin, Monatsb. (1872), p. 319; 1873b, Akad. Berlin, Abhandl. (1872), Pl. 10, fig. 17.
Theoconus zancleus (Müller) Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 1399.
Theoconus zancleus J. Müller?, Popofsky, 1913, Deutsche Südpolar-Exped., vol. 14, pp. 397-398, Pl. 38, figs. 6, 7.
?Lithornithium clausum Popofsky, 1913, Deutsche Südpolar-Exped., vol. 14 , pp. 393-395, text figs. 111-116.

Cephalis with prominent dorso-lateral lobes, a straight dorsal face merging with a three-bladed apical horn, four collar pores, and three indistinct thoracic ribs extending as short spines above the base of the thorax. Cephalis closed at the top, with smooth surface and small, unequal to subequal, circular pores. Vertical spine indistinct but present; apical horn not robust. Thorax campanulate to truncate-conical, separated from the cephalis above by a change in contour and from the abdomen below by a distinct constriction occupied by an internal septal ring. Surface of thorax smooth. Thoracic pores ranging from circular and subequal to subpolygonal and increasing slightly in size distally with regular hexagonal arrangement in longitudinal rows. Abdomen smooth, ranging from subcylindrical with its distal portion tapering inward and with equal (6-12 µm) circular pores arranged hexagonally in longitudinal rows to truncate-conical with distal portion broader and not constricted and with polygonal to subpolygonal pores having the same arrangement but gradually increasing in size distally (from about 6-8 µm to 20-26 µm).

Measurements; based on 30 specimens from stations 27 and 34: length of cephalis 21-39 µm, of thorax 36-49 µm, of abdomen 37-143 µm; breadth of cephalis 21-32 µm, of thorax 64-80 µm, of abdomen 75-119 µm; length of apical horn 9-36 mm, of vertical spine 0-5 µm, of dorsal and primary lateral spines 0-12 µm.

Remarks. The species listed in the synonymy are all similar in their presence of a cephalis with a straight dorsal face merging with an eccentric apical horn, a campanulate thorax, and an abdomen either dilated or constricted distally and separated from the thorax by a stricture occupied by an internal septal ring. None of the illustrations of these species shows the dorso-lateral lobes, but in several specimens from the Gulf they are inconspicuous. Only the illustrations of Eucyrtidium cranoides Haeckel, Pterocanium sabae Ehrenberg, and Lithornithium clausum Popofsky show the dorsal and primary lateral thoracic ribs, but these features are not readily observed in all specimens from the Gulf and then only in apical or basal views.
No specimens from the Gulf have their basal mouths closed by a lattice, but in all other aspects several are similar to Lithornithium clausum Popofsky in that they have an abdomen that is constricted distally and has equal pores throughout (Pl. 33, fig. 4). If further study reveals that these forms have their terminal mouths closed, they should be separated and assigned to Popofsky's species.

Distribution. This species (or species-group?) occurs as far north in the Gulf as station 192. It is absent at stations 130, 191, 194, and all those to the north. It is common at stations 27 (2.0%), 34 (4.2%), 46 (4.4%), 56 (3.2%), 60 (2.8%), 81 (3.0%), 92 (3.0%), 93 (2.2%), 99 (2.6%), and 151 (2.0%) and rare to nearly common at all other stations except 184 and 192 where it is very rare. It is, therefore, a common member of the Gulf assemblage, but its average frequency is greater in the southern half of the Gulf than in the northern half. Its relatively high frequency at stations located in the northern Gulf diatomite facies suggests that its occurrence in this region is related to upwelling. In the southern half of the Gulf it occurs with greater frequency in the axial portion rather than near either coast with the exception of stations 56, 92, and 99 which are located within or near known regions of upwelling.
The species listed in the synonymy have been reported from the tropical regions of the Atlantic, Pacific, and Indian Oceans as well as from the Mediterranean Sea. This species or species-group is thus widespread in Recent tropical seas.
Benson 1966











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