Beresellaceae

Beresellaceae is an extinct family whose biological classification remains uncertain. It has occasionally been considered part of Metazoa (multicellular animals), but is provisionally grouped with the green algae order Dasycladales. Beresellids had a worldwide distribution, with fossils appearing in deposits from the late Devonian through the early Permian.

These organisms formed calcareous, cylindrical tubes, each 100 to 400 micrometers in diameter and up to 5 millimeters long. The tubes were usually single, rarely paired, and contained an axial canal that frequently became filled with clear calcite during fossilization.

Identification relies on their distinctive two-layered walls and verticils—blind pores that branched outward from the cylinder. A mucilaginous coating likely surrounded the living organism, preserved in fossils as transparent calcite cement. As of 1998, no reproductive structures had been discovered for this group.

During the middle Carboniferous, beresellids became significant producers of marine carbonate sediment, often found alongside various phylloid algae. They are believed to have thrived in shallow, sheltered lagoons. In some areas, their local accumulations were extensive enough to be classified as beresellid bafflestone or packstone, marking this family as a rock-forming group of algae.