An attempt of classification of the Palaeozoic incertae sedis Algospongia

The Algospongia have in common morphological and palaeoecological affinities with different extant groups but no real modern equivalents among the foraminifers, protists, red algae, green algae or calcisponges. The class is based on the following shared characters: 1) similar wall (yellowish, apparently granular); 2) functional apertures (especially a lateral or terminal aperture) which permits
the communication between successive chambers or cells; 3) frequent wall perforations; 4) apical growth; and 5) sessile or attached mode of life. Their description is controversial because of the uncertain assignment. The small size of perforations excludes them as calcisponges or microstromatoporoids. They have many characters in common with the foraminifers: e.g., external calcification, potential uniseriate chambers, and terminal aperture. Nevertheless, they differ by the absence of a proloculus, type of calcite unknown, and general evolution. The attribution to other protists remains difficult because of the absence of modern equivalents and the often huge productivity, a character more generally attributed to the algae. However, some similarities with the Xenophyophora are noteworthy. If assigned to the algae, the Algospongia cannot correspond to green algae because of their abundance in dysphotic or aphotic marine environments. They can appear as a group closely linked to red algae because of living depths, some morphological similarities (“cellular” network of Ungdarella), and the great variety of groups assigned to the fossil red algae (solenoporaceans, moniliporellaceans,katavellaceans). Following this assignment to red algae, the apertures of the Aoujgaliida are generally considered as synapses; the wall as an equivalent of the cell calcification in the corallinales; attachment bracelets as conceptacles. Moreover, it becomes possible to explain by comparison with the modern corallinales: 1) the abundance of the aoujgaliids, 2) their commonly associated shelter porosities, 3) endosymbiotic filaments, 4) their habituses (often attached or dwelling in soft substrates). Nevertheless, these supposed similarities are only subjective, and counter-arguments can be always presented. The class Algospongia includes two orders and six suborders, previously described at least as families: Moravamminida [with four suborders, Wetheredellina, Moravamminina (=Palaeosiphonocladales), Beresellina, and Donezellina], and Aoujgaliida (with two suborders, Aoujgaliina and Calcifoliina). These orders and suborders are briefly described, discussed, and in some cases emended. The families Asphaltinidae and Cuneiphycidae are created. Four new genera and eight new species are described. They are (in alphabetical order), Costacheoides, Denisella, Fasciolium, Multiporidium, Aoujgalia woodlandensis, Asphaltinoides falgairasensis, Calcifolium castelsequense, Fasciella desquamata, Fasciolium pantherinum, Multiporidium dilectum, Tubus avesnellensis, and Wetheredella? munneckei.