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Amphitholus acanthometra
Haeckel, 1887
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Description - Add description
Amphitholus acanthometra Haeckel
Central chamber about twice as broad and as high as both cupolas. On the surface quite symmetrically distributed twenty long and strong cylindrical radial spines; eight in the sagittal plane or in the meridan plane of the central chamber (four opposite in pairs in the principal and sagittal axes, four others in the middle between the principal and sagittal spines); four in the horizontal transverse plane, on both sides of the poles of the major or lateral axis; and eight in diagonal planes (corresponding to the eight wing-spines of Tetrapyle octacantha). In the centre of the central chamber is a distinct trizonal medullary shell like that of Tetrapyle, with two vertical columella beams. Pores of the cortical shell subregular, circular, with elevated hexagonal frames about four times as broad as the bars; five to seven in the semicircle of one cupola. (This remarkable species differs from Tholartus vicenus in the possession of a medullary shell, from Amphitholniun acanthometra by the simple cortical shell. Copare these species)
Dimensions.—Major axis of the shell 0.14 to 0.16, minor axis 0.10 to 0.12; pores 0.015, bars 0.004; major axis of the medullary shell 0.04 to 0.05, minor (horizontal) axis 0.02 to 0.03; length of the twenty radial spines 0.18 to 0.24, basal breadth 0.01.
Habitat.—South Pacific, Station 300, depth 1375 fathoms.
| | Haeckel 1887 | Amphitholonium tricolonium Haeckel
Outer cortical shell smooth, of the same three-jointed form as the inner, at an equal distance from it throughout the whole circumference; central chamber higher-vaulted than both cupolas. Network of the outer shell delicate, with subregular, circular pores. Pores of the thick-walled inner shell subregular, circular, with hexagonal frames, three times as broad as the bars; eight to ten in the basal semicircle of one cupola.
Dimensions.—Major axis of the outer cortical shell 0.2, minor axis 0.15; major axis of the inner cortical shell 0.16, minor axis 0.11; pores 0.01, bars 0.0035.
Habitat.—South Pacific, Station 302, depth 1450 fathoms.
| | Haeckel 1887 | Benson, 1966, p.258-260; pl. 17, figs. 4-7:
Amphitholus acanthometra Haeckel
Amphitholus acanthometra Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 667, Pl. 10, figs. 5-6.
Amphitholonium tricolonium Haeckel, 1887, Challenger Rept., Zool., vol. 18, p. 669, Pl. 10, fig. 7.
Interior ellipsoidal shell a single system of dimensive girdles originating from a small inner ellipsoidal shell or ring-like structure. Second transverse girdle completely within the interior of shell and merges laterally with and forms a part of the sagittal ellipsoidal shell covering it and the inner trizonal shell; this shell in frontal view appears discoidal (P1. 17, fig. 5) with the two smaller dome-shaped cupolas on either side of it. Pores of the shell subcircular to subpolygonal, about equal in size, with subregular arrangement. Surface of shell generally with short thorns. In most specimens 14 regularly disposed primary beams generally continuous as radial spines are recognizable (see remarks for description); in other specimens beams thinner, more numerous, but most of the primary beams generally recognizable. Radial spines not present in all tests but present in most, their number variable from 4-100 or more, but generally only the primary spines continue inward as beams; spines conical, of variable breadth and length (5-50 µm). In a few specimens a thin, small-pored outer mantle envelops the cortical shell; it is supported by the radial spines arising from the cortical shell and is separated only a short distance from the shell.
Measurements; based on 18 specimens from stations 27, 34, and 71 (all measurements are of frontal views only): length of P1 axis 9-12 µm, of P2 axis 27-42 µm, of P3 axis (major diameter of sagittal ellipsoidal shell) 71-98 µm, of T1 axis 6-10 µm, of T2 axis 14-25 µm, of T3 axis (minor diameter of sagittal ellipsoidal shell) 42-58 µm, of maximum transverse axis (distance between tangents to the lateral cupolas) 80-121 µm, of axes S2, S3, and S4 (one specimen) 11 µm, 36 µm, and 82 µm, respectively; breadth of cupolas (measured parallel to the principal axis) 55-80 µm.
Remarks. Haeckel (1887, pp. 666-668) describes several species of Amphitholus, all of which are defined on the presence or absence of radial spines and on the number of radial spines in the case of the former. The Gulf species of this genus has a variable number of radial spines, and in some specimens they are absent. The Gulf specimens, however, are generally smaller than those described by Haeckel. Because this species is rare in the Gulf, its complete range of variation could not be determined. Radial spines which appear to be primary, i.e., continuous inward as cylindrical radial beams, are generally 14 in number in the Gulf specimens. These include six mutually perpendicular spines which are arranged in pairs, oppositely placed, and coaxial with the three dimensive axes of the test, and eight diagonal spines corresponding to those observed in a few specimens of Tetrapyle octacantha. In other specimens, radial beams are thinner, more numerous, and are less regularly disposed, in a few specimens not continuous as radial spines. Haeckel illustrated only three species of Amphitholus of which A. acanthometra is most similar to the Gulf species although it is slightly larger and has 20 regularly disposed spines, six of which may be secondary. The other species described by Haeckel may be identical to the Gulf forms, but without their illustrations it is impossible to make this decision.
A few specimens of the Gulf species have a thin outer veil covering and conforming to the shape of the cortical shell. Although Amphitholonium tricolonim Haeckel is slightly larger than the Gulf specimens, it was included in the synonymy.
Additional remarks (Benson, 1966, p. 257). The genus Amphitholonium Haeckel becomes a junior objective synonym of Amphitholus Haeckel because its type species, Amphitholonium tricolonium Haeckel, is placed in synonymy with a species from the Gulf identified as Amphitholus acanthometra Haeckel. Because the development of the outer mantle is subject to intraspecific variation, it cannot be used as a character defining a genus.
Distribution. This species is rare in the Gulf but occurs as far north as station 151, being absent at all those to the north as well as at station 90. Its rare occurrence prohibits analysis of control of its distribution by upwelling. Because it has a much greater frequency in the southern half of the Gulf, it is considered an oceanic species.
Amphitholus acanthometra and Amphitholonium tricolonium were reported by Haeckel from the South Pacific at "Challenger" stations 300 and 302, respectively, in waters of the Humboldt Current off the coast of Chile. Thorough study of the taxonomy of Haeckel's species of both genera is needed before conclusions regarding the world-wide distribution of this group can be made.
| | Benson 1966 |
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