REDESCRIPTION OF ZOOTHAMNIUM-NIVEUM (HEMPRICH AND EHRENBERG, 1831) EHRENBERG, 1838 (OLIGOHYMENOPHORA, PERITRICHIDA), A CILIATE WITH ECTOSYMBIOTIC, CHEMOAUTOTROPHIC BACTERIA

A very large and fast growing species of Zoothamnium Bory de St. Vince nt, 1826 (Oligohymenophora, Peritrichida), Z. niveum (Hemprich & Ehren berg, 1831) Ehrenberg, 1838 has been discovered in mangrove channels o f the Caribbean Sea, the Gulf of Mexico, and the Red Sea. This colonia l, sessile ciliate is remarkable for its obligatory association with e ctosymbiotic, chemoautotrophic, most likely sulfur-oxidizing bacteria covering almost the entire body of the host. Two distinct morphotypes of bacteria - rods and cocci presumably representing only one species, are present. A redescription of Z. niveum is made based on live obser vations, silver carbonate stainings after Fernandez-Galiano [29], and scanning electron microscopy. Z. niveum is characterized by a feather- like colony, a stalk which is often divided, branches occurring altern ately on the stalk, and an alternate arrangement of zooids on the bran ches. Three different types of zooids are present: microzooids and und ividing terminal zooids with a slender, strongly asymmetric oral side; roundish to ellipsoid macrozooids; and ellipsoid dividing terminal zo oids. All have a striped silverline system with pellicular pores and a macronucleus with a unique shape. The oral ciliature turns 1 1/4 in a clockwise direction when viewed from inside the cell. The ciliature o f the microzooids consists of a paroral membrane, three adoral membran elles (polykineties), one stomatogenic kinety orally, and one circular irregular row of barren kinetosomes aborally (trochal band). The cili ature of the macrozooids is the same as in the microzooids, except for an additional long epistomial membrane orally and a telotrochal band of several circular rows of kinetosomes aborally. A comparison of morp hological characters within the genus Zoothamnium is provided, with sp ecial attention given to different forms of epigrowth on various repre sentatives of this genus.