Hexapyle dodecantha group
Description - Add description
|Benson, 1966, p. 275-278; pl. 18, figs. 14-16; pl. 19, fig. 4(?); text-fig. 20:|
Hexapyle dodecantha Haeckel
Hexapyle dodecantha Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 569, Pl. 48, fig. 16.
Py1odiscus triangularis Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 570, Pl. 48, fig. 17.
Test consisting of a double pylodiscid shell; with outer shell larger than that of Discopyle ? sp. but with similar arrangement of twelve radial spines and, in several specimens, with one, two, or three radial beams each extending across the tubular spaces through the shell; with or without a large but irregularly-pored lattice covering the surfaces of the outer shell (text-fig. 20). Latticed covering, when present, with numerous (50 or more) radial spines arising from its surface and branching at a common level; in a few specimens, the branches of these spines anastomose to form part of an outer triangular or ellipsoidal latticed shell which was never observed fully developed; completely developed tests, therefore, not discoidal. Innermost structure within first pylodiscid shell not observed but may consist of a central node from which radiate the three radial beams mentioned above.
Measurements; based on 9 specimens from stations 27, 71, 81, and 92: length of base of inner triangular pylodiscid shell 18-43 µm, of outer pylodiscid shell 80-137 µm, of altitude of inner shell 20-42 µm, of outer shell 74-128 µm; length of base of outer triangular shell covering double pylodiscid shell 113-185 µm, of altitude 122-154 µm.
Remarks. This species differs from Discopyle ? sp. in the larger outer pylodiscid shell and the lack of a spongy network developed beyond this shell and the outer shell; the outer shell of this species is not a relatively smooth ellipsoid as in the preceding species but a somewhat irregular, generally subtriangular shell. Specimens conforming.to Haeckel's illustrations of Hexapyle dodecantha and Pylodiscus triangularis as well as several which show intergradations from the former (without latticed cover) to the latter (with latticed cover) were observed. Because Hexapyle is the earlier described genus and H. dodecantha has page priority over P. triangularis, the former was chosen as the nominal species. The two species of Discopyle that were
illustrated by Haeckel (1887, Pl. 48, figs. 19-20) may be similar to if not the same as Hexapyle dodecantha instead of Discopyle ? sp., but this could not be investigated because of the difficulty in observation of the inner triangular shells and the lack of access to Haeckel's type material.
Distribution. Identification of this species presents the same problem, i.e., one of orientation, as in Discopyle ? sp. The frequency of this species in the Gulf, therefore, may be greater than actually indicated. Numerous, relatively large ellipsoidal shells were counted as a group designated as Litheliacea unidentified (Pl. 1, no. 67) if some indication of inner latticed girdles were observed. These specimens, therefore, may include representatives of Phorticium pyloniuxn, Discopyle? sp., Hexapyle dodecantha, and Larcopyle bütschlii. This group is common to rare at all stations in the Gulf except 203 and 204 where it is absent. It occurs in greater numbers in the southern Gulf; thus it is parallel to the distribution of the members comprising it.
Specimens identifiable as Hexapyle dodecantha occur rarely in the Gulf but as far north as station 192. None were observed at stations 64, 115, 130, 191, 194, and those to the north. They occur with greater frequency in the southern Gulf and, therefore, may prefer oceanic water masses.
Both Hexapyle dodecantha and Pylodiscus triangularis were reported by Haeckel from "Challenger" station 270 in the central Pacific. Their apparent absence in high latitudes indicates that they may be confined to tropical regions.
|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.
|Remarks. Fully developed individuals with an outer ellipsoidal shell of smooth outline (Benson, 1966, pl. 18, figs. 12, 13, 16; this chapter, Plate 6, Fig. 6) may closely resemble fully developed individuals of Phorticium pylonium and Larcopyle butschlii.|