  The calcareous alga Donezella is composed of thin (typically 70-160 micrometer in diameter) branching segmented tubes, which bifurcate at an angle of 45-90
degrees. This calcareous alga is known to baffle sediment and build small (~6 m thick) to large (30-100 m thick) bioherms. Examples of Donezella-dominated
bioherms are reported from Middle Carboniferous strata of Algeria, the Canadian Arctic Archipelago, Spain, and West Texas. 
     A 5 m thick Donezella - siliceous sponge bioherm from the Wapanucka Formation was studied in detail by microfacies analysis. Due to high dip of the beds, the lateral dimension of the bioherm is not known. 
The bioherm overlies thin (20 cm), cross-bedded crinoidal-bioclastic packstone to grainstone, and is capped by peloidal packstone to grainstone The bioherm is primarily composed of Donezella boundstone-bafflestone and peloidal wackestone. In situ siliceous sponge bodies are locally preserved in the lower part of the buildup, by encrustation of micritic crusts and the red alga Archaeolithophyllum. Siliceous sponge spicules are common in the lower half of the bioherm and are rare to present throughout the upper half of the bioherm. The presence of siliceous sponge bodies in the lowest part of the buildup strongly suggests that they played a significant role in initial mound accretion. 
     The green calcareous alga Donezella is common to abundant throughout the bioherm. Donezella builds a delicate framework or colony of thalli enclosing constructional pores. These pores are filled with internal sediments, burial calcite cements, dark micritic crusts and peloids with fuzzy outlines. Toward the top of the bioherm Donezella is increasingly surrounded by carbonate mud. Worm tubes with dark, micritic, encrustations are common in Donezella colonies. 
     The calcareous alga Berestovia (or Claracrusta) is present mainly in the lower half of the bioherm, acting as the primary and secondary encruster of siliceous sponges. Berestovia is also the primary encruster of Donezella colonies. The red alga Archaeolithophyllum is locally present as the secondary and tertiary encruster of siliceous sponges in lower part of the bioherm. Broken segments of Archaeolithophyllum and other phylloid algae are increasingly present toward the top of the bioherm, often encrusted by encrusting foraminifera. 
      Ostracod, benthonic, and encrusting foraminifera are rare to present, but are increasingly present toward the top of the bioherm. Brachiopods, ramose bryozoans, crinoids and corals are rare to present, and are scattered irregularly throughout the bioherm. 
     The bioherm shows a subtle vertical community succession from Donezella boundstone to peloidal wackestone in the lower 5/6 of the bioherm to wackestone
with scattered Donezella, fragments of phylloid algae, ostracodes and foraminifera toward the top. This succession is interpreted as being due to shallowing. The presence of siliceous sponge bodies, the abundance of siliceous sponge spicules, and the lack of high-energy microfacies in this bioherm indicates initiation and growth in a quiet-water environment below storm-wave base in the open-marine / slope environment seaward of the platform-margin grainstone belt. 
