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Antarctissa strelkovi Petrushevskaya, 1967

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This species has structure typical for the genus. First segment separated from second by indistinct constriction. Width of "cephalis" 2 /3 72 of width of "thorax." Pores on first and second segments round, disposed randomly, their dimensions varying greatly. Walls of shell comparatively thin. Surface with spines and even long supplementary needles. These needles arising on first segment, extending laterally at sides of second segment and hanging down beneath its lower edge (in specimens in sediment needles are broken off rather close to base). Elements of internal skeleton far more slender than in A. denticulata and their external extensions more distinct.
Dimensions: length of first segment (externally) 45-55μ, width 60-65μ, length of second segment 70-90μ, width 70-110μ overall length of shell up to 150μ.
Location. Noted by Popovskii (1908) as one of the most numerous species in Antarctic plankton at 0-385m horizons. In Antarctic sediments found by Riedel (1958) at stations 30, 42, 47, 94, 97, and 103 of BANZARE. In our material encountered in plankton at stations 183, 184, 186, 187, 246, 249, 272, 274, 287 of the "Ob' " at 10- 500m horizons. This species was extremely numerous (dozens of specimens in preparation). Found in sediments of all stations in Indian and Pacific Ocean sectors of Antarctic. In Antarctic shelf sediments (Figure 86,II) shells of A. strelkovi constitute from 25 to 70-76% of total number. Proportion of these shells in deepwater sediments is 4-6%. A. strelkovi restricted in its distribution to the Antarctic and not encountered in warm water regions.
Holotype in the ZIN collection, preparation No. 1 of station 29 of the "Ob' . "
Note. This species was defined by Popovskii (1908) and by Riedel (1958) as Helotholus histricosa Jorgensen. However, in the North Atlantic these forms are not encountered: the specimens present there (Figure 51, II) differ from the Antarctic specimens, as noted above, by the ratio of the first and second segments, the arrangement, size, and number of pores, and in particular by the structure of the elements of the internal skeleton, and the junction between the "cephalis" and "thorax." Therefore we conclude that the species described from the North Atlantic by Jorgensen (1905) is separate and that the nassellarians encountered in the Antarctic should not be numbered among it but should be described as a new species - A.strelkovi . It is most similar to A.denticulata, but differs from it by the presence of long supplementary needles on the surface, the general form of the shell, and the thinner skeletal wall.
This is named after the soviet protistologist Aleksandr Aleksandrovitch Strelkov.
After this work had gone to press, Hays (1965) defined this same species as Helotholus histricosa Jorgensen, apparently following Riedel. However, Riedel himself (1958) did not consider this definition indisputable or conclusive. Hays write that he was unable to detect in the north Atlantic -the region from where the typical Helotholus histricosa was described- such forms of Helotholus histricosa as those distributed in the Antarctic (i.e. A.strelkovi in our opinion). In fact, A.strelkovi is absent in the north Atlantic. Typical specimens of Helotholus histricosa, however, are distributed, albeit in small amounts, in sediments of the Norwegian sea.
Petrushevskaya 1967


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