Ultrastructure and morphogenesis of the marine epibenthic ciliate Epiclintes ambiguus (Epiclintidae, n. fam.; Ciliophora)

Abstract

Epiclintes ambiguus, a highly contractile marine ciliate, has ventral cirri in oblique and marginal rows, and three rows of dorsal cilia, thus is at the hypotrich structural grade. We use light microscopy of living and protargol stained specimens and both scanning and transmission electron microscopy to describe cortical morphogenesis through cell division and interphase cortical structure of E. ambiguus. Cortical morphogenesis proceeds in 2 oblique developmental zones and is based on 4 kinds of primordia: oral, frontal, somatic, and a specialized ventral primordium. Thirteen to fifteen oblique rows of ventral cirri arise primarily from somatic (within-row) primordia (producing the anterior complement of cirral rows) and the ventral primordia (producing the posterior complement of cirral rows); frontal ciliature is limited to one or two short cirral rows. A longitudinal series of transverse cirri differentiate from posterior kinetosomes in (1) frontal streaks, (2) ventral (within-row) streaks, and (3) streaks that develop from ventral primordia. Stomatogenesis in the opisthe begins near the cell surface, then continues within a cortical pit which lengthens posteriorly. Stomatogenesis in the proter occurs dorsally to the parental buccal membranelles. The ultrastructural organization of membranelies and cirri of Epiclintes is consistent with the general structural pattern within the Spirotricha. Dorsal ciliary complexes are dikinetids with the anterior kinetosome ciliated, the posterior nonciliated; each dorsal cilium protrudes from a cylindrical cortical papilla. Dikinetids have postciliary, transverse, and nematodesmal microtubules as well as a kinetodesmal fiber. Nematodesmal granules (d = 55 nm) lie beside nematodesmal microtubules. A system of multilayered, membrane-like materials lie within the cortex. Stomatogenesis, deployment of somatic ciliature, and general organization of microtubular structures in Epiclintes suggest an evolutionary relationship with Kahliella and other members of the Stichotrichina. Morphogenetic and structural specializations however justify inclusion of Epiclintes in a new family, the Epiclintidae.