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).

Algospongia (vernacular name: algosponges) is a taxon of calcified fossil organisms comprising around 90 accepted genera and several hundred species,[1] treated taxonomically as a single class in an unspecified phylum.

[3][4] 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.

[1] 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.

[5][6] 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.

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.

: Aoujgaliales) is characterised by Vachard & Cózar as follows (emended description): Attached, laminar to cylindrical or conical, bifurcated tests, composed of rows of chambers forming laminae, with a concentric or uniseriate growth.

The system of attachment, generally unknown or constituted by a whorl of chambers around the substrate (e.g., Kettnerammina, Moravammina); by "bracelets" (Dil et al., 1977) (Exvotarisella, Ardengostella); or rarely, it is encrusting (Evlania).