Lotharella polymorpha sp nov (Chlorarachniophyta) from the coast of Portugal

Lotharella polymorpha was isolated from a sample of marine sediment collected at Sao Rafael, Albufeira, Portugal, in July 1998. Typical characteristics of a chlorarachniophyte alga are: chloroplasts containing chlorophylls a and b and lutein, the presence of a nucleomorph between the outer and inner pair of membranes surrounding the chloroplasts, and uniflagellate zoospores. In L. polymorpha, the nucleomorph is located in a periplastidial compartment beside the base of the pyrenoid. The pyrenoid is divided into two halves by the inner pair of chloroplast membranes. The position of the nucleomorph and the structure of the pyrenoid indicate that the new isolate belongs to the genus Lotharella. Lotharella polymorpha differs from the other species L. amoeboformis and L. globosa in the shape of the sessile cells and at the subcellular level. While amoeboid stages and meroplasmodia are lacking in L. globosa, L. polymorpha forms a meroplasmodium with two differently shaped types of sessile walled amoebae. Coccoid cells, migrating amoebae, heliozoan-like cells and zoospores also occur. Stellate amoeboid cells, as described for L. amoeboformis, were not detected. The pyrenoids of L. polymorpha have no stalks and their capping vesicles are filled with an amorphous substance. Sessile amoebae have a thick, compact, and electrondense cell wall with pores. Because of these specific characteristics, we describe the first isolate of Lotharella found in the Atlantic Ocean as a new species, L. polymorpha.