This class contains a group of one-celled animals which may secrete an [exoskeleton] (external protective covering) of [chitin], [silica], or calcium carbonate. Included in this class are foraminiferans (commonly called forams) and radiolarians.
Order Foraminifera.—
Members of this order secrete tiny chambered shells which are very useful microfossils. The forams are predominantly marine organisms and have shells composed of [chitin], [silica], or calcium carbonate. In addition, some forms construct a shell of sand grains or some other material which is cemented together by a sticky substance that is secreted by the animal.
Forams are very abundant in the rocks of Texas and particularly so in rocks of [Mesozoic] and [Cenozoic] age. The most numerous and easily observed [Paleozoic] foraminiferans are the fusulinids ([fig. 9]a), and their small spindle-shaped remains are very abundant in many of the [Pennsylvanian] limestones of north-central and Trans-Pecos Texas. Some typical Texas forams are illustrated in [figure 9].
Order Radiolaria.—
The radiolarians ([fig. 10]) have delicate spine-covered shells composed of [silica], and their remains are very abundant in certain recent marine sediments. They may also be found as fossils and have been reported from [Devonian] and [Permian] rocks in Trans-Pecos Texas, and probable radiolarians have been reported from still younger beds.
Fig. 9. Typical Texas Foraminifera (all greatly enlarged). (a) Fusulina ([Pennsylvanian]). (b) Robulus. (c) Globigerina. (d) Frondicularia. (b-d, [Cretaceous]).
Fig. 10. Typical radiolarians (greatly enlarged). (a) Actinomma (Recent). (b) Porodiscus ([Eocene]).