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Siphostichartus corona (Haeckel, 1887)

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Cyrtophormis corona
Shell smooth, conical, ovate, with three deep strictures, about twice as long as broad. The fourth joint is the broadest, inflated, and three times as long as the second and the third joints. Pores small and numerous, circular, in regular, transverse rows; two in the first joint, four in the second and third, and ten in the fourth joint. Cephalis hemispherical, with a stout, pyramidal horn. Peristome two-thirds as broad as the fourth joint, with twelve to fifteen triangular, convergent teeth.
Dimensions.-Length of the shell (with four joints) 0.16, breadth 0.08. Length of the single joints, a 0.01, b 0.03, c 0.03, d 0.09.
Habitat.-Western Tropical Pacific, Station 225, depth 4475 fathoms
Haeckel 1887
Siphostichartus corona
Description: Shell smooth, hyaline, conical, compressed laterally. Cephalis hemispherical with a few circular pores, well-developed three-bladed apical horn, and prominent, duck-billed vertical tube; apical spine free of cephalic wall and axial rod well developed. Thorax inflated, slightly heavier than the rest of the shell; two or three transverse rows of circular pores. Abdomen inflated conical with four to seven transverse rows of circular pores. Fourth segment considerably larger than the others, usually contracting distally and without a differentiated peristome; numerous widely spaced transverse rows of small circular pores. Termination ragged or shell may terminate along a pore row. thus giving the appearance of small terminal "teeth" (cf. Riedel and Sanfilippo. 1971. p. 1600). Intersegmental strictures curved, not pronounced internally.
Dimensions: Total length (excluding apical horn) 135- 190: length of abdomen 30-40: length of fourth segment 70-105; maximum breadth (across fourth segment) 70-95.
Range and abundance: Rare at time of first appearance in the Stichocorys wolffii Zone; few to common from Dorcadospyris alata Zone to Ommatartus penultimus Zone; last rare occurrences in the Stichocorys peregrina Zone.
Phylogeny: Appears to have developed from Siphostichartus praecorona in whi ch the third segment has only two rows of pores and a less prominent apical horn and vertical tube.
Remarks: Petrushevskaya and Kozlova (1972. p. 538) have described a similar form, Theocamptra spirocyrtis. In the present study no specimens quite like it have been observed.
Nigrini 1977











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