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Sphaerozoum punctatum Müller, 1858

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Benson, 1966, p. 286-287; pl. 19, figs. 12-13:

Plagonium cf. sphaerozoum Haeckel

?Plagonium sphaerozoum Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 916, Pl. 91, fig. 6.

Test consisting of a straight smooth cylindrical rod (median bar?) with a verticil of three undifferentiated, divergent spines arising at each end, all of nearly equal length, circular in section, but with numerous short thorns arising from along their complete extent.

Measurements; based on 5 specimens from station 93: length of central rod (median bar?) 15-20 µm, of spines 55-98 µm.

Remarks. The length of the central rod is much smaller than that of Plagonium sphaerozoum Haeckel. Haeckel’s illustration of this species shows additional branches of the secondary spines of the main spines arising from the central rod, but no specimens from the Gulf were observed with this character. This species is rare in the Gulf; therefore, its complete range of variation could not be investigated.
Haeckel (1887 p. 916) states that species of the genus Plagonium Haeckel are remarkably similar to the isolated spicules of certain colonial Spumellina, e.g., Lampoxanthium punctatum and Sphaerozoum punctatum. Without study of the living specimens of this species from the Gulf, one cannot determine whether it is a nasselline or spumelline form. Its rare occurence at any station in the Gulf suggests that it is a solitary nasselline species rather than a colonial spumelline. For this reason it was placed in the former but only tentatively identified as Plagonium sphaerozoum because of its shorter central rod and lack of branches on the secondary spines.

Distribution. This species is very rare in the Gulf, occurring only at stations 34, 46, 64, 81, 93, 106, 115, 133, and 151. Except for station 64, all are located within the axial part of the Gulf; therefore, this species is not associated with upwelling and appears to be oceanic.
Haeckel reported P. sphaerozoum from the equatorial Atlantic. Because identification of the Gulf forms with this species is not positive, nothing further can be concluded about their world-wide distribution except that they are at least tropical.
Benson 1966


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