| Home> Cenozoic> Miocene>
 

List species

Actinomma livae Goll and Bj°rklund, 1989

Description - Add description

Diagnosis: A species of Actinomma characterized by a small, sphaerical, well-defined outer medullary shell joined to the large multi-layered cortical shell by numerous stout, bladed radial beams; some of which penetrate the outer cortical shell as short spines.
Etymology: The species is named in honor of Liv Baeve, spouse of KRB.
Description. Skeleton consists of three or four spherical concentric lattice shells configured as inner and outer medullary shells and one or two cortical shells. The diameters of the three inner shells have an approximate ratio of 1:2:5. The structure of the inner medullary shell is obscured by the cortical shells and can not be observed on complete specimens. The outer medullary shell is relatively thick walled and clearly defined as a regular lattice shell, perforated by small, round, densely-spaced pores. On many specimens, fine lattice spines project radially from the outer medullary shell and may have a length approximately one-half the distance to the inner margin of the cortical shell. Additionally, numerous prominent, bladed, irregularly disposed radial beams project from the medullary shell and are joined to the robust, inflated and loosely perforated cortical shell, which may be single or paired. The two cortical shells have similar composition. On specimens with two cortical shells, the major radial beams penetrate the inner cortical shell and are joined to the inner wall of the outer cortical shell. Some of these primary radial beams penetrate the outer cortical shell as short, stout lattice spines. A multitude of secondary radial beams span the space between the cortical shells. The distance between the inner and outer cortical shells varies considerably. The ratio of these two diameters ranges from 1:3 to 1:7.
Remarks: In the development of paired cortical lattice shells, Actinomma livae closely resembles Actinomma holtedahli, from which it is distinguished by the spherical perforate outer medullary lattice shell. Specimens of A. holtedahli are characterized by a loosely reticulate outer medullary lattice shell draped between the dense array of delicate radial beams.
Size: 273-296 μm, maximum diameter of the outer cortical shell.
Occurrences: Actinomma livae has a sparse occurrence in 104-642D-2X-CC and occurs sporadically within the interval from Samples 104-642B-25H-1, 75-77 cm to -1H-5, 25-26 cm; and from Samples 104-643A-17H-1, 25-27 cm to -16H-2, 105-107 cm.
Holotype: PMO 117.576; Sample 04-643A-16H-5, 105-107 cm; England finder W30/4; PI. 1, Figs. 1-3.

Goll and Bj÷rklund 1989


Description

 

Images

 

Synonyms

 

References

 

Distribution

 

Discussion / Comments

 

Web links