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Artostrobus annulatus (Bailey, 1856)

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Shell elongated, digitiform or somewhat conical, with a rounded apex and terminal spine. Cells or perforations arranged in transverse lines, four to six being visible at once in each ring.
(Bailey) 1856
Skeleton cylindrical or narrow-conical. First segment "cephalis", small, devoid of pores, with irregular swellings. Externally "cephalis" indistinctly demarcated from remainder of shell. Portion of shell directly following "cephalis" either devoid of pores or with small pores disposed irregularly. Next follows main part of shell on which pores are disposed in characteristic transverse rows. Pores oval, elongated along axis perpendicular to longitudinal axis of shell. Number of rows of pores reaches 16, as specially noted by Riedel. No internal partitions corresponding to transverse rows of pores within shell. All of the hundreds of specimens examined displayed signs of prolonged growth, which suggests that the skeleton in Artostrobus annulatus continues to grow throughout life.

Internal skeleton consisting of basic elements (needles MB, D, Lr and L1, A, and Vert) always present. These needles are very slender, often curved; their directions varies. External extensions of needles of internal skeleton producing apical horn (needle A) and lateral processes (needles D, Lr and L1). Length of these processes varies greatly.

Dimensions: length of first segment 15-17 micrometer; overall length of shell up to 160 micrometer, maximum width 30-35 micrometer.
Petrushevskaya 1967


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