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Description of Pleurotricha lanceolataPleurotricha lanceolata (Ehrenberg, 1838) Stein, 1859 Description; Pleurotricha lanceolata has an inflexible dorsoventrally flattened body and has a lengthened oval shape with a rounded anterior end and a bluntly tapered posterior end. The nuclear apparatus has two ellipsoidal macronuclear nodes. Two spherical micronuclei lie very close to them. The adoral zone of membranelles (AZM) begins close to the right antero-lateral margin and continues to the front end of the body, forming a curve which borders the peristome and finishes slightly to the left of the antero-posterior axis of the ciliate. This structure consists of 45-55 membranelles. The right side of the peristome bordered by the outer paroral membrane and the inner undulating membrane (endoral membrane). Both membranes are about the same length although they begin at different levels, because only the endoral membrane reaches the posterior apex of the peristome. Each one has two closely packed rows of kinetosomes. There is a row of left marginal cirri that begins towards the middle of the body, surrounds the left margin, and ends at the ciliate\'s posterior end. The right margin a cirri are arranged in two or three rows. One surrounds the external right margin and the other lies to the left of the outermost right marginal row which begins at the same level as the first membranelle of the AZM, ending in the ciliate\'s posterior end. The second (medial) right cirral row is shorter. In some individuals supernumerary cirri occur medial to the innermost cirral row. In some individuals with 3 right cirral rows the second row terminates at half the length of the cell and the innermost (3rd) row has a few widely spaced cirri in its anterior part and more closely spaced cirri in the posterior half. Pleurotricha lanceolata has 13 frontoventral cirri, 8 frontal cirri and 5 ventral cirri (3 postoral cirri and 2 pretransverse cirri). There are 5 transverse cirri separated into an anterior group of 3 and a posterior group of 2. Although previously described as lacking caudal cirri, there are, in fact, 3 caudal cirri, each consisting of 4-6 rows of kinetosomes, on the dorsal surface to the right of the midline. They are located at the termini of dorsal kinety 1,2 and 4 respectively and arise from these kineties during morphogenesis. The caudal cirri of the adult are resorbed. The dorsal somatic infraciliature consists of 6 rows of dikinetids. Rows 3,5 and 6 do not reach the posterior end. The anterior basal bodies bear a bristle ~3-4 Âµm long and the posterior basal bodies are bare. The resting cysts are yellowish brown, ~ 65 Âµm in diameter, adorned with blunt, irregular spinous projections ~ 9 Âµm long.