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Euchitonia sp. Benson, 1983

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Benson, 1966, p. 232, 234-235; pl. 14, figs. 3-4:

Euchitonia mülleri Haeckel

Euchitonia mülleri Haeckel, 1862, Die Radiolarien, pp. 508-510, P1. 30, figs. 5-10; Popofsky, 1912, Deutsche Südpolar-Exped., vol. 13, pp. 137-138, text fig. 54, not text figs. 52 and 53.

Test comparable in size and symmetry to Euchitonia elegans. Central region circular, consisting of 5-7 concentric, latticed, discoidal shells; arms with 8-32 (number dependent upon degree of development of test) concentric, irregular rings similar to those of E. elegans. The two arms opposite the odd arm straight, not bent toward one another; arms similar in shape but slightly broader and thicker than those of E. elegans , therefore appear more spongy. Spongy layered patagium generally incomplete or rudimentary, rarely absent; in fully developed forms it is shaped like a spherical triangle and has a thickened margin, being thinner and more distinctly layered, proximally. Only one specimen observed with terminal spines arising from the arms, 2-3 per arm, 4-25 µm in length.

Measurements; based on 30 specimens from stations 46, 60, 64, 71, and 81: angle A 123°-152°, mean 137°; angle B 66°-116°, mean 86°; angle C l20°-148°, mean 138°; ratio of angle A to B 1.07-2.03, mean 1.60, of angle C to B 1.03-2.15, mean 1.60; diameter of outer concentric shell of central region 70-105 µm; length of odd arm 71-256 µm, of each of the two similar arms 71-252 µm and 64-247 µm; minimum breadth of odd arm 36-68 µm, of each of the two similar arms 31-63 µm and 32-68 µm; maximum breadth of odd arm 49-102 µm, of each of the two similar arms 39-95 µm and 43-93 µm; length of base of triangular test 156-520 µm, of altitude 187-520 µm; maximum breadth of complete patagium 207-375 µm.

Remarks. In size, symmetry, and shape of the fully developed patagium this species does not differ from Euchitonia mülleri Haeckel (1862, pp. 508-510, P1. 30, figs. 5-10). Haeckel's illustrations, however, show the central region consisting of 3-4 concentric rings, not unlike those of Euchitonia elegans. In certain Gulf specimens the central region appears to be composed of concentric rings rather than shells, a feature which shows clearly in specimens with fewer concentric shells. Haeckel does not indicate the presence of concentric rings in the arms whereas Popofsky (19l2, text fig. 54)
does. Stöhr's (1880, P1. 5, fig. 5) illustration of E. mülleri is similar to the Gulf species, but the patagium appears to be composed of a much denser spongy network with thicker trabeculae; therefore, his species was not included in the synonymy.

Distribution. This species is cosmopolitan in the Gulf, occurring at all stations except 90, 203, 206, and 214. It is common (2.0%) at station 27 and rare at all other stations. Its frequency in the southern Gulf is slightly greater than its average frequency in the northern half of the Gulf, although it undergoes a definite increase at station 184. It does not undergo significant increases in frequency at stations located within regions of known upwelling. Its decrease northward in the Gulf indicates its greater affinity for oceanic waters.
Haeckel (1887, p. 533) states that this species is cosmopolitan apparently in tropical regions only, including the Mediterranean Sea. Popofsky reported this species from the South Atlantic off the west coast of Africa. Because it has not been reported from high latitudes it is confined to tropical regions of all seas.
Benson 1966
Benson, 1983, p. 503:

Remarks. This species(?) is distinguished by: its large size; its circular central structure consisting of five to seven concentric, latticed, discoidal shells; its two similar arms which do not bend toward one another; and, in fully developed tests, a patagium with thickened margins, convex outward between the arms, presenting the appearance of a shield. It is clearly not the same as E. mülleri (=E. furcata) of Nigrini (1967); therefore, I have designated it as Euchitonia sp.
Benson 1983


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