Microfossils of Uncertain Affinity 



Discoosteridae (PI. 11 -IV, fig. 17) 



The Discoasteridae are minute, stellate, calcareous structures with shapes 

 ranging from radially-ribbed, imperforate plates to starlike bodies consisting of 

 4 to 8 arms. They are found in Cretaceous and Tertiary marine rocks, and are 

 probably the skeletal remains of extinct, unknown planktonic microorganisms. 

 Like the calcareous microforaminifera, they are found also in the residues pre- 

 pared for plant spores and pollen. When treated with 52 percent hydrofluoric 

 acid, their tests change from calcium carbonate to calcium fluoride. When more 

 is known about the discoasterids they should be useful in paleontological labora- 

 tories. 



Hystrichospherids (PI. 11 -IV, figs. 18-22) 



The hystrichospherids, a group of microfossils of unknown biological af- 

 finities, are becoming an important tool in oil exploration. These minute fossils 

 have been recognized in rocks ranging from the pre-Cambrian to Recent. Little 

 is known of the hystrichospherids except that they occur in brackish to marine 

 sediments, and, therefore, are important as paleoecological indicators. Early 

 workers such as Ehrenberg in 1836 thought they were fresh-water algae. Merrill 

 in 1895 considered them to be sponge spicules, while Lohman in 1904 compared 

 them with the spring eggs of marine planktonic Crustacea. In 1933, Wetzel 

 described them as remains of unknown organisms related to the dinoflagellates. 



Though many hystrichospherids are simple spheres or elliptical structures, 

 others have morphological characteristics such as spines, which make them di- 

 agnostic and easily recognized. Their most frequent occurrence is in shales, 

 cherts, limestones, and dolomites ; but they are also found in siltstones and sand- 

 stones. To the stratigrapher, hystrichospherids are especially useful in the Lower 

 Paleozoic rocks where other microfossils often are scarce or absent. The preser- 

 vation of hystrichospherids is frequently very complete, and because of their 

 minute size they can be recovered from well samples where other microfossils 

 are destroyed. 



In general, many Lower Paleozoic forms are minute, smooth, spherical-to- 

 elliptical bodies belonging to the genus Leiosphaera. Middle Paleozoic forms 

 have spherical to triangular bodies with large simple spines or arms that attenu- 

 ate from the central body. The Upper Paleozoic hystrichospherids generally 

 have larger central bodies, which are smooth or covered with many sharp spines. 

 The genus Hystrichosphaera, whose vesicle wall consists of plates, is character- 

 istic of the Mesozoic. Cannosphaeropsis, a genus with the processes branching 

 and joined at the tops, thereby forming a netlike cover around the vesicle, is 

 found in the Mesozoic and Tertiary. There is also some evidence that it may ex- 



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