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Dictyophimus bicornis (Ehrenberg, 1861)

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Skeleton consisting of two portions. First segment, "cephalis," with small apical horn, needle Vert, and some supplementary needles; not sharply delimited from second segment in region of their junction are irregular swellings, as in D. gracilipes. Width of first segment half that of second. Second segment usually closed below. Pores rounded, somewhat irregularly shaped, smaller, on first segment while on lower surface of second segment very large. Pores disposed irregularly. Five to six pores located in spaces between points of emergence of needles D and L or LT and L1 through wall of second segment. Internal skeleton consisting of usual basic elements (needles MB, D, LT and L1, A, and Vert). These elements closely fused to walls of shell. Needles D, LT and L1 passing to outside approximately at middle of second segment. Diverging laterally below at fairly obtuse angle.

Dimensions:
Length of first segment (externally) about 15 μ, width 33 40 μ; length of second segment up to 60 μ, width 55 63 μ.

Location:
Found by Ehrenberg in sediments near Greenland. Haeckel (1887) reports this species from sediments of temperate zone of North Atlantic, but unfortunately does not provide a drawing of the specimen he found. Encountered in our material in almost all samples of Antarctic sediments in both Indian and Pacific Ocean sectors, but shells are few. Not encountered in tropical-zone sediments. This species was encountered rather more frequently in our North Atlantic material than in the Antarctic samples.

Notes:
The Antarctic specimens differ slightly from the North Atlantic
specimens by their smaller number of larger pores. Our species is most similar to D. gracilipes. The complex junction of the first and second segments is very similar, the second segment in both is usually closed, and the needles of the basal tripod in both species project to the outside lateral to the second segment. D. gracilipes and D. bicornis differ in that in D. bicornis the pores are larger and fewer and also the needles of the basal tripod are weaker and shorter; they pass through the wall of the second segment higher up and are directed somewhat more horizontally than in D. gracilipes. However, if we compare our species with the typical species of genus Lithomelissa Ehr., 1847 (those similar to L. thoracites) and with Dictyophimus gracilipes (type species of genus Dictyophimus), it is clear that in the general construction of the shell this species is closer to Dictyophimus than to Lithomelissa.

Petrushevskaya 1968


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