Phylloid algal-Tubiphytes mounds (shelf margin).
Sponges and cements are rare.

Abstract ref. 2012:
   Spectacular phylloid algal reefs of Virgilian and Wolfcampian age occur in the Hueco Mountains, Texas. These are dominated by the erect, recumbent or
cyathiform chlorophyte genera Eugonophyllum and Ivanovia. 
     Such reefs have long been considered as ecologically simple communities, that lack dominant framebuilders, but contain substantial volumes of micrite. As a result,
the dominant constructional mechanism for reef formation has been inferred to be sediment baffling and trapping, mainly by erect phylloid algae. However, detailed
analysis of growth framework clearly shows that these algae were in fact capable of forming a rigid framework. Phylloid algae, together with the problematicum
Tubiphytes/Shamovella and the red alga (?) Archaeolithoporella, formed complex, multiple encrustations (both in-vivo and post-mortem) and were a fundamental
element of reef construction. Furthermore, crypts formed by Eugonophyllum, were frequently colonised by pendant Tubiphytes/Shamovella encrustations. Typically,
crypt-dwellers were smaller and less well developed than their open surface representatives. This demonstrates the limited longevity of such crypts before their
occlusion by internal reef sediments and early marine cements. 
     Synchronous gamete production and release is demonstrated for Eugonophyllum individuals and colonies. By analogy with modern relatives such as Halimeda and
Udotea, Eugonophyllum colonies suffered post-reproductive mass-death. This is due to holocarpic reproduction, where the plant undergoes simultaneous conversion
of the entire cell contents into gametes. The life cycle of Eugonophyllum may therefore be split into three phases: 1. Rapid colonisation of substrate by settlement of a
limited number of zygotes. 2. Growth and calcification of the plants. 3. Sexual reproduction and resulting mass-death of the plants. The resulting algal detritus is an
important sediment component in both the reef and surrounding off-reef facies. The amount of carbonate production due to these phylloid algae is probably similar to
the reported values for modern Halimeda, where a modest vegetation density of 1 kg/m2 produces calcareous sediment at a rate of 2 kg/m2/yr. Therefore,
construction of these Palaeozoic algal reefs is due to many superimposed communities representing repeated, self-seeded colonisation. The Eugonophyllum plants
themselves grew within a rapidly lithifying, micritic substrate. Indeed, such rapid seafloor cementation was clearly essential for reef formation and may have provided
a mechanism of substrate attachment for the Eugonophyllum plants. 
     These observations show that reef formation can arise from many different mechanisms resulting in in-situ carbonate production and therefore complex feedback
controls are important determinants of reef fabric. However, much remains to be understood as to the relative importance of constructional versus destructional
processes in ancient reefs. Careful application of uniformitarian models to these reefs is required. From a biological viewpoint, uniformitarian models may be invoked
in determining the life history of phylloid algae. However, from a geochemical viewpoint, rates of cementation and seawater chemistry in these icehouse reefs are
likely to be very different to present-day conditions. Therefore, many of the processes involved in the construction of these algal reefs may be unique to these
Palaeozoic reefs. 