[TERTIARY] CORALS
ENDOPACHYS × 1 ASTRHELIA × 1 FLABELLUM × 1 MICRABACIA × 2 TROCHOSMILIA × 1
In Texas one may expect to find bryozoan remains in the [Pennsylvanian] rocks of north-central and Trans-Pecos Texas where they are abundant in certain of the marine shales and limestones. Bryozoans may also be collected from some [Cretaceous] and [Tertiary] beds, but their remains are small and fragmental and they are easily overlooked. Bryozoans have also been found matted on the shells of [fossil] mollusks and other invertebrates.
[Phylum] Brachiopoda
The brachiopods are a large group of exclusively marine organisms with shells composed of two pieces called valves ([fig. 13]). These valves are usually composed of [calcareous] or [phosphatic] material and enclose and protect the soft parts of the [brachiopod] animal. The soft parts are composed of muscles, the [mantle] (which secretes the valves), digestive, [respiration], reproductive, and excretory organs, and the tentacle-bearing [lophophore].
In adult life the [brachiopod] is attached to the sea bottom by means of a fleshy stalk called the pedicle ([fig. 14]), and this is usually extruded through a hole (the pedicle [foramen]) which is located in the [ventral] or pedicle [valve]. The upturned area which is usually present on the pedicle valve is called the beak. The other valve, known as the [dorsal] or brachial valve, is usually the smaller of the two ([fig. 13]b). The two valves are opened by means of muscles, and since death results in relaxation of these muscles, [fossil] brachiopods are typically found with valves closed.
Brachiopods vary greatly in size and shape and exhibit a wide [variety] of ornamentation, such as spines, ribs, nodes, and other structures. They are abundant fossils in many of the [Paleozoic] rocks of Texas but are relatively rare in [Mesozoic] and [Cenozoic] formations.
The [phylum] has been divided into two subclasses, the Inarticulata and the Articulata. This classification is based upon the nature of the [hinge-line]—the edge of the shell where the two valves articulate.
Fig. 13. Morphology and principal parts of articulate brachiopods.