Summary

A new species of endolithic cyanobacteria, Hyella racemus sp. nov. (order Pleurocapsales), penetrates ooid grains in actively shoaling sands in shallow (0.5-5 m) waters of the Bahama carbonate platform and the Arabian Gulf. Hyella racemus is characterized by prolific branching, resulting in dense grape-bike cell clusters that penetrate the carbonate substrate. The clusters radiate inward and form deep, isodiametric pits. Resin casts of these pits are framboid (raspberry-like) in shape. The borehole morphology conforms with the shape of the endolith body and can be identified in resin-cast preparations. Cell division is by cleavage with regular alternation of division planes. The sheath is tight, layered, and colorless or yellow-brown when under strong illumination. The new species is one of the most common endoliths in ooids of the Bahamas and the Arabian Gulf. It differs from other members of this endolithic genus by its branching pattern and less prominent apical cells