Comprehensive DescriptionRead full entry
DescriptionArtostrobus jörgenseni: Skeleton consisting of two segments. First segment small, sometimes with small rounded pores on its surface, sometimes apex completely lacks pores. At point of junction of first and second segments irregular swellings seen, but junction simple, wall of "cephalis" passing directly into wall of second segment. In this section of shell pores scattered irregularly. On following part of second segment pores rounded or oval, often extending in direction perpendicular to axis of shell; grouped in distinct transverse rows. Second segment with irregular outline, expanding slightly downwards. Internal skeleton composed of slender, well developed needles MB. D, Lr and Ll, A and Vert. Needle A forming apical horn and needles D, Lr and Ll forming lateral processes of slender (often broken off). Dimensions: length of first segment 12-15µm, width about 20µm, length of second segment up to 90µm, width (below) 45-50µm. Note: This species is similar to Artostrobus annulatus. In both shells is elongate, the ratio of the first and second segment the same as is their function; pores in both disposed in transverse rows. Basic difference between our species and A. annulatus is the presence in A. jörgenseni of pores in the upper part of the shell (first segment and region of junction with second), absent in A. annulatus, and the larger and denser pores on the second segment of A. jörgenseni than on that of A. annulatus. In addition, the second segment itself expands markedly inferiorly. The elements of the internal skeleton are more developed than in A. annulatus. However, these differences are not great and our species may be related to genus Artostrobus, as it is similar to A. annulatus, the type species of the genus.