ABSTRACT: Ultrastructure o/Pleurosigma chilensis var. patagónica nov. var. (Bacillariophyceae).
The genus Pleurosigma has a few planktonic species, with straight or almost straight outline and rap
he. In this work we study a material with these characteristics from Caleta Valdés (Chubut, Argenti
na), that we consider a new variety of Pleurosigma chilensis Hustedt et Krasske.
Pleurosigma chilensis var. patagónica nov. var. differs from P. chilensis by its bigger size, with a
wider range as regards the number of striae, a bigger and very conspicuous circular central area and
bigger helictoglossae. Comparissons with the nearest species are established: P. simplex Ricard and P.
intermedium Smith.
The samples were cleaned with the conventional methods and analized with optical and electronic
scanning microscopy.