Morphological Studies Indicate that Pleuronema grolierei nov. spec. and P. coronatum Kent, 1881 Represent Different Sections of the Genus Pleuronema (Ciliophora: Scuticociliatida)

Abstract

The morphology, infraciliature and silverline system of two marine scuticociliates, Pleuronema grolierei nov. spec. and Pleuronema coronatum Kent, 1881, isolated from the sand beaches along the coast of Qingdao, China, were investigated using live observation and silver impregnation methods. Ciliates of the genus Pleuronema are normally easily recognized by their large sail-like paroral membrane. In this respect, P. coronatum is a typical member of the genus, whereas P. grolierei is unique in having much shorter cilia in the paroral membrane, which, in consequence, is rather inconspicuous. Nevertheless, details of the infraciliature confirm that P. grolierei belongs to the genus Pleuronema. Within the genus Pleuronema, the posterior end of the anterior fragment of the second membranelle (M2a) may be either straight, as in P. grolierei, or hooked-shaped, as in P. coronatum, providing a criterion for recognizing two sections within the genus. Based on the current study and previous reports, we propose that three nominal forms, Pleuronema balli Small and Lynn, 1985, Pleuronema smalli Dragesco, 1968 and Pleuronema borrori Dragesco, 1968 should be synonymized with P. coronatum.