Specimens of Craspedostauros indubitabilis. (Lange-Bertalot & Genkal) E.J. Cox from a sample taken in Bahia Salada, Caldera, Chile (27 degrees 38'S-71 degrees 00'W) were acid cleaned and examined by light and electron microscopy. The genus and the species are reported for the first time from Chilean marine coastal waters. Craspedostauros was described in 1999 by Cox for some marine biraphid diatoms previously placed in Stauroneis Ehrenberg and Stauronella Mereschkowsky. The genus is recognized by its cribrate areolae, narrow stauros, numerous girdle bands and two chloroplasts fore and aft of the central cytoplasm. According to the Chilean material, Craspedostauros indubitabilis is characterized by its linear-elliptic to lanceolate valves usually with rounded ends, the striae (22-30 in 10 mu m) are parallel in the valve centre and slightly convergent near the apices, the areolae adjacent to the raphe are much larger than over the rest of the valve, each areolae is occluded by 3 to 13 pores, and a knob of silica separates the central internal raphe endings. A diagnosis is here included for this taxon based on the characteristics observed in the Chilean material. The presented photomicrographs aim to provide information about the main morphological features.