High Pressure Freezing and Freeze Substitution of Primitive Agglutinated Foraminifera

Abstract

Freeze substitution techniques can provide exceptional fixation of many types of small biological materials. Ultrastructural studies on the Foraminiferida (marine rhizopods) traditionally have used standard chemical fixation protocols. The relatively large size (-25 μm - several cm) and the presence of a mineralized shell in most taxa precludes the application of many cryo-techniques. High pressure freezing, however, provides a method for freezing organisms as large as many of the smaller foraminifera often without extensive ice damage. Gamonts (sexual generation) from three representatives of the suborder Astrorhizina ﹛Myxotheca sp., Cribrothalammina alba, and Hyperammina sp.) were selected because they are among the most primitive foraminifera and have only very finely agglutinated shells with non-mineralized, organic cements. Myxotheca sp. and C. alba were originally collected from salt marsh environments on Sapelo Island, Georgia, and Hyperammina sp. was isolated from fine-grained carbonate sediments of the Florida Keys.