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Actinomma kerguelenensis Caulet, 1991

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Description: Skeleton consists of four concentric spherical shells. Outermost (fourth) shell always present, thin walled with small pores of irregular size and form, more or less spiny. Cortical (third) shell with irregular, thickly-framed pores commonly polygonal. At the junction of the pore bars, there are small nodes which extend to the outer shell. Distance between the fourth and the third shells short (1/3 of the distance between the medullary and cortical shells). Medullary (second) shell thin-walled with subcircular to circular pores, almost equal in size. Surface smooth, with scattered needle-shaped by-spines. Innermost shell consists of an irregular mesh, connected to the medullary shell by thin radial beams which are strongly developed outward from the medullary shell. These radial beams are about 10-15 in number and three-bladed. Radial beams extend beyond the fourth shell as main spines. Outer length of these spines no longer than the distance between the cortical and medullary shells.
Remarks: A. kerguelenensis is easy to distinguish from other Eocene/Oligocene actinommids by its large size and the two cortical shells. It differs from A. holtedahli (an early Miocene actinommid with two external shells described by Björklund (1976) from the Arctic sediments), by the presence of an internal medullary shell.
Name: After the geographic location (Kerguelen Plateau).
Occurrences: Upper Eocene to upper Oligocene at Sites 738 and 744 (Tables 4 and 6). The FCO was not observed, but is probably located in the middle to upper Eocene (a barren interval at Site 738). LCO is in Sample 119-744A-14H-1, 53-55 cm (late Oligocene). No evolutionary transition was observed. Abundant to rare.
Dimensions: Outermost shell diameter: 235-292 µm (mean value: 263 µm); outermost shell pore diameter: 4-25 µm; cortical shell diameter: 182-240 µm (mean value: 204 µm); cortical shell pore diameter: 10- 30 µm: medullary shell diameter: 96-105 µm (mean value: 100 µm); medullary shell pore diameter: 8-10 µm; external spine length: 50-120 µm.
Types. Holotype (MNHN no. F61368), Sample 119-744A-15H-1, 53- 55 cm, 3-Z50/4, (PI. 1, Fig. 1). Paratypes: (MNHN no. F61369 and MNHN no. F61370), Sample MD 83481, 3.40 m, 1-V27/3, (PI. 1, Fig. 2), and Sample 119-744A-16H-4, 53-55 cm, 1-D35/1
Caulet 1991











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