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Cycladophora cosma cosma
Lombari and Lazarus, 1988
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Description - Add description
Description: Cephalis is simple, of medium size, subspherical with numerous subcireular pores and two bladed apical horns. The horns arc 1.5-2 times the diameter of the cephalis in length and one of them possesses thorns. Cephalis is slightly depressed into upper thorax creating a weak spinal furrow. Lateral spines may be expressed externally. Upper thorax is compressed, weakly flared and flat (uncurved or straight) in outline with irregular to subcireular pores. They are small though non-uniform and are irregularly arranged near the cephalis becoming staggered in horizontal rows. A gradual, weak pore size gradient increases distally. Pores may have a thin interior lattice. Pore bars are of moderate width and thickness and they are free of spines, costac and sponge. Upper thorax suture is unconstricted. Lower thorax is elongate (i.e. taller than wide), weakly to moderately flared and flat in outline. Pores arc hexagonal in shape, medium to large in size, and arranged in staggered horizontal rows. A gradual, strong pore size gradient increases distally. Pores near the top of the lower thorax may have a thin interior lattice. Pore bars arc narrow and of medium thickness with no ornamentation. Abdomen or terminal segment consists of one row of large, open, hexagonal pores. However, this segment is rarely complete. There is one row of short basal spines and no basal plate is observed.
Type: DSDP Site 173, core 28, section 3, 144 cm. England finder number P6/3.
Origin of name: From the Greek noun kosmos, world. Named for its cosmopolitan nature.
Comments: C. c. cosma is similar to C. c. irregularis in size and shape and in possessing pores with interior lattice. However, C. c. cosma has pores which are consistently arranged in regular horizontal rows and which are of regular shape. Also, C. c. cosma has one apical horn which possesses thorns, while this is not a consistent feature in C. c. irregularis. C. c. cosma appears to be closely related to Cycladophora davisiana cornutoides and Cycladophora davisiana semeloides. However, Hays (pers. comm.) has found that C. davisiana does not evolve until the middle Pliocene. Since C. c. cosma is found throughout the Miocene, it will not be synonymized with post-Miocene forms until further investigation is completed.
Occurrence: Found in DSDP site 173-29-2, 41 cm through 173-14-2,71 cm, Site 116-13-CC through 116-8-3, 137 cm, Site 278-25-CC through 278-9-CC, Site 266-22-CC through 266-18-CC. Cycladophora c. cosma is abundant throughout the Miocene in the well-preserved high-latitude material studied. It is a truly cosmopolitan high-latitude species.
| | Lombari & Lazarus 1988 |
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