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Hexapyle dodecantha group Haeckel, 1887

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Benson, 1966, p. 271-274; pl. 18, figs. 11-13; text-fig. 19:

Discopyle ? sp.

Fully developed forms (text-fig. 19) consisting of an internal single pylodiscid shell joined by an irregular loose spongy network to a large, ellipsoidal shell which is generally smooth, except for scattered, short, conical to three-bladed spines or thorns and has a thin wall and irregular, unequal pores; the presence of a pylome could not be determined. Small single pylodiscid shells without the surrounding loose spongy network were grouped with the above forms because they appeared to be incompletely developed. The inner shell or chamber consists of a triangular ring as described under the family Pylodiscidae. In several specimens 12 radial spines are present, arising in pairs from the lateral margins of each of the six gates. A few specimens have radial beams which arise from the inner ring or chamber and extend across the tubular spaces through the shell. Pores of the half-girdles irregular.

Measurements; based on 11 specimens from stations 27, 71, 81, 136, and 184: inner triangular ring: length of base 16-38 µm, of altitude 17-37 µm; outer pylodiscid shell: length of base 47-89 µm, of altitude 47-86 µm; major diameter of outer ellipsoidal shell 101-212 mm, minor diameter 62-197 µm.

Remarks. This species should be regarded instead as a species-group because single pylodiscid shells were grouped with those having the outer ellipsoidal shell. The internal pylodiscid structure of the latter becomes apparent only after the specimen has been rolled under the microscope; therefore, in permanent slides they are not easily recognizable. Several but not all specimens of Larcopyle bütschlii Dreyer were first observed with an irregular trizonal internal structure but when rolled under the microscope the pylodiscid shell became apparent in a certain position. In fixed slides, therefore, the two species cannot be distinguished unless the pylodiscid shell is in a favorable orientation for observation.
This species-group was placed tentatively in the genus Discopyle Haeckel mainly because specimens with ellipsoidal shells resemble Haeckel's illustrated species of this genus (1887, Pl. 48, figs. 19, 20). Whether or not the single pylodiscid shells represent a separate species could not be determined, but they are similar in all respects to those inside the ellipsoidal-shelled forms.

Distribution. Most of the specimens identified in the counts represent the small single pylodiscid shells. Some specimens identified and counted as Larcopyle bütschlii Dreyer may belong to this species-group, however, as discussed above.
This species-group is cosmopolitan in the Gulf. It is absent only at stations 90, 203, and 214. It is common at stations 27, 34, 56, 60, 71, 92, and 93, and it is rare at all others. It is the third most abundant species at station 34 where it has its highest frequency (4.6%) in the Gulf. In the southern Gulf, where its average frequency is greater, it is present in greater numbers at the offshore or deep water stations and does not increase at stations located within regions of upwelling. In the northern half of the Gulf it is rare at all stations, nearly common at a few, and undergoes no significant changes in frequency. It thus appears to have a greater affinity for oceanic than for Gulf waters, and its distribution is not controlled by upwelling.
Both species of Discopyle described by Haeckel (1887, pp. 572-573) were reported from the central Pacific. Without positive identification of the Gulf species-group with them, little can be stated about the world-wide distribution of the former except that it is at least a tropical group.











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