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Stylatractus cronos (Haeckel, 1887)

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Benson, 1966, p. 182-183; pl. 7, figs. 12-13:

Xiphatractus cronos (Haeckel)

Amphisphaera cronos Haeckel, 1887, Challenger Rept., Zool., vol. 18, p.144, P1. 17, fig 5.

Test consisting of three ellipsoidal shells with two unequal, three-bladed to conical polar spines which continue inward to the second shell as heavy three-bladed radial beams and to the first shell as thinner beams. The shells are joined by numerous thin beams which arise at the nodes of the intervening bars of both the first and second shells; some beams continuous from first shell to third, some from first to second, others only from second to third. Polar spines generally three-bladed, of variable length and breadth, in nearly all specimens of unequal size; no accessory radial spines present. Outer shell generally ellipsoidal, in a few tests spherical, generally with thorns at the nodes of the intervening bars, in a few tests with smooth surface; with large, equal, subcircular to polygonal pores, hexagonally arranged, 6-9 on half the minor circumference, generally with polygonal frames. Second shell ellipsoidal, with subequal, polygonal to subpolygonal, hexagonally arranged pores, 6-8 on half the minor circumference, with polygonal frames. Inner shell ellipsoidal, with subregularly arranged, subequal polygonal pores, 6-8 on half the minor circumference.

Measurements; based on 30 specimens from stations 27, 34, and 46: major dianeter of outer shell 107-139 µm, of second shell 62- 84 µm, of inner shell 31-46 µm; minor diameter of outer shell 90-123 µm, of second shell 57-79 µm; length of greater polar spine 15-96 µm, of lesser polar spine 2-85 µm; breadth of base of spines 7-25 µm.

Remarks. This species differs from Xiphatractus pluto in the thinner wall of the cortical shell (3-5 :m), the lack of small, circular, secondary pores filling the spaces of the larger pores of the cortical shell, and in generally less robust polar spines. Haeckel describes Amphisphaera cronos Haeckel as having a smooth, spherical, cortical shell, but a few specimens from the Gulf also were observed with smooth, spherical, cortical shells, although the majority have ellipsoidal thorny shells. The dimensions he gives are in agreement with those of the Gulf specimens.

Distribution. This species occurs rarely only in the southern half of the Gulf at stations 27, 34, 46, 56, 60, 64, 71, 90, 91, 93, and 95. It is absent at all other stations. Its highest frequency was observed at station 90, but this may be the result of fewer species present at this station rather than of upwelling. It is, therefore, a rare member of the tropical Pacific fauna and is not tolerant of water masses with higher salinity and temperature.
Haeckel (1887, p 1L~4) reported this species from “Challenger” station 330 in the southern Atlantic. Since the taxonomy of this species is not well-known, its worldwide distribution cannot be assessed. Several of Haeckel's species are similar to this and Xiphatractus pluto. Further taxonomic study of this species-group is needed.
Benson 1966











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