Algospongia is a class of small, calcified fossil organisms of uncertain taxonomic position, assigned in a comprehensive 2010 review to "Animalia" incertae sedis (possibly Protista), but both prior to and post that to an unnamed phylum of Algae; other workers simply list them as Problematica (or Microproblematica). They occur in carbonate rocks of the Paleozoic era and their last representatives occur in the Late Permian geological period. Characteristic genera include Aoujgalia, Moravammina and the early-appearing Wetheredella, although the taxonomic validity (and algosponge affinity) of the last named genus has been disputed.
Background and possible taxonomic affinity
Algospongia (vernacular name: algosponges) is a taxon of calcified fossil organisms comprising around 90 accepted genera and several hundred species, treated taxonomically as a single class in an unspecified phylum. Originally considered to be fossil sponges or "pseudo algae", an assignment now refuted, their taxonomic position is somewhat unresolved. Of the three most prominent recent researchers, B. Mamet (Belgium) assigns certain families (e.g. Palaeoberesellaceae, Beresellaceae and Issinellaceae) to Chlorophyta (green algae) as an order of that phylum (Palaeosiphonocladales), at least one other family (Ungdarellaceae) to Rhodophyta (red algae), and some other genera (Groenlandella, Labyrinthoconus) simply to "Microproblematica". Meanwhile, D. Vachard (France) and P. Cózar (Spain) treated Algospongia (such as the family Calcifoliaceae) as Algae incertae sedis, before deciding (in 2010) against any algal affinity and reassigning them to the [zoological] protists, as a group possibly paralleling the Foraminifera. Since that paper, Cózar has continued to use zoological terminology in his published works, while Vachard has once again assigned the group to the Algae incertae sedis, lying hypothetically mid-way between the extant Rhodophyta and Chlorophyta. A number of the genera allocated to Algospongia in the present treatment (which follows Vachard & Cózar, 2010 in the main) were recently (2021) treated as either Foraminifera, or as red or green algae, in the World Register of Marine Species, a situation that is currently under revision. For convenience in the present article, the published summary of Vachard & Cózar (2010) is presented below (with modifications as necessary), which treats the relevant genera as a single class (not split e.g. among different botanical phyla) under zoological nomenclature, however also recognizing that the botanical treatment now preferred by Vachard may in fact be correct, an approach recently adopted in the Interim Register of Marine and Nonmarine Genera (IRMNG) and reflected in the taxon box supplied with this article.
Members of the group occur in the fossil record from the Ordovician to the Late Permian periods, although only Wetheredella is promininent prior to the start of the Devonian. They share a common wall appearance (frequently perforated), possess functional apertures between successive chambers or cells, and appear to have had a sessile or attached mode of life, at depths considered too deep for green algae but possibly overlapping those of red algae, while morphologically they do not exactly resemble members of either of those groups. The most comprehensive recent taxonomic treatment of the group is by Vachard & Cózar, 2010, in which they are treated as a single class divided into 2 orders (Aoujgalida and Moravamminida, corresponding to Aoujgaliales and Moravamminales in botanical nomenclature) typified by the genera Aoujgalia and Moravammina, respectively, plus a number of suborders; this treatment is reproduced below, together with adjustments based on more recent literature of relevance.
Morphology
Algosponges are described as a group of sessile or attached microorganisms with characteristic calcified walls described as "yellowish, apparently granular" that are frequently perforated, and possess either lateral or terminal apertures between successive chambers or cells. The order Aoujgalida (bot.: Aoujgaliales) is characterised by Vachard & Cózar as follows (emended description):
while the order Moravamminida (bot.: Moravamminales) is described as follows (emended description):