The taxonomy of the diatom Lacunicula sardiniensis Lange-Bertalot, Cavacini, TagliaventietAlfinito and its relationship with the genus Craticula Grunow (Bacillariophyceae)

Abstract

A new diatom genus typified by the new species Lacunicula sardiniensis Lange-Bertalot, Cavacini, Tagliaventi et Alfinito was recently described by Lange-Bertalot and collaborators from ephemeral pools in Sardinia, Italy. The new genus is mainly characterized by the presence of an external channel system found in the axial area on both sides of the raphe fissure. We present here a detailed analysis of a North American population of the same species from Zollner Creek, Oregon. Based on light microscopy (LM) and scanning electron microscopy (SEM) data, it is proposed that the mentioned species be placed in the genus Craticula Grunow instead. Lacunicula sardiniensis shares many characteristics with species currently placed in Craticula; among them are: 1) the characteristically raised axial area in both internal and external views, 2) the presence of a conopeum along the axial area of the valves, 3) the similarity of areolar and velum patterns and characteristics in both external and internal views of the valves, 4) the similarity in the structure of the raphe and helictoglossa, and 5) the presence of longitudinal ridges on the valve mantle and valve face. Thus, the new combination Craticula sardiniensis (Lange-Bertalot, Cavacini, Tagliaventi et Alfinito) Morales et Le is proposed and the relationship of the taxon with closely related species in the genus Craticula is presented in the light of available literature.