Observations on the Fine Structure of Two Species of the Peritrich Ciliate Genus Scyphidia and on Their Mode of Attachment to Their Host

Abstract

An electron microscopical study of two representative species of the peritrich family Scyphidiidae, Scyphidia ubiquita and S. inclinata n. sp., is presented. Special attention has been paid to the structure of the holdfast organelle of these ectoparasitic ciliates, the scopula. In both species, the scopular disc is a very prominent structure. Its adhesive surface (= the scopula proper) is covered by a pellicle which is highly modified, if compared with the rest of the body, and has quite flat pellicular pores. In S. ubiquita the scopular kinetosomes are rather anomalous in that they are of a much shorter shape than the rest of the somatic and buccal kinetosomes; and scopular cilia are not at all developed. The scopular surface secretes a substance for attachment of the ciliate to the surface of its host. In S. inclinata the scopular kinetosomes are of a size conforming to the kinetosomes of the rest of the body, and they give rise to long scopular cilia of typical ultrastructure. These cilia are firmly wedged among the microvilli of the surface of the host's body, assuring firm attachment of the ciliate. The structural peculiarities described for the two species may be regarded as genuine adaptations to the ectoparasitic way of life. Thanks to electron microscopic studies of different representatives of stalkforming sessiline peritrichs (e.g., on Campanella, Opercularia, and Zoothamnium by Faure-Fremiet, Rouiller & Gauchery, 1956a; on Epistylis, Opercularia, Carchesium, and Vorticella by Randall & Hopkins, 1962; on Epistylis, Zoothamnium, and Carchesium by Faur6-Fremiet, Favard & Carasso, 1962; to cite the most significant), the principles of organization of the scopula and the way it produces the stalk are well known in these ciliates. However, there have been no data available to date on the structure of this organelle in those peritrichs whose scopula is directly attached to the substrate throughout the whole time of their adult life, e.g., in some representatives of the family Ophrydiidae, the Lagenophryiidae, and in all members of the Scyphidiidae (Corliss, 1961). While a large number of papers based on light microscopal observations have been concerned with the formation and appearance of the stalk and lorica of peritrichs, the data on structure of the scopula in species of Scyphidia are very scarce. When looking for a comprehensive description, we have to go as far back as Faure-Fremiet's (1905) classical paper published 63 years ago. According to that old and yet still valid characterization of Faure-Fremiet's, the suckershaped scyphidian scopula contacts the surface of the host's body only by its free borders: from the vaulted center of the scopula extends a brush of 2-3 /, long, immobile cilia, which touch the surface of the host by their slightly swelled ends. The ends of the scopular cilia are supposed to be capable of secreting a substance which, in effect, glues the ciliate to the host's surface. Evidence for the secretion of such a substance was found in the fact that the swollen ends of the scopular cilia were stained by Congo red. No essential data have since been added to Faure-Fremiet's careful original observations. An electron microscopic study of scyphidians appears of interest, therefore, 1 Much of the work reported here was supported by National Science Foundation grants GB-2800 and GB-7013X awarded to the junior author. TRANS. AMER. MICROSC. Soc. 87(4): 493-509. 1968. This content downloaded from 207.46.13.142 on Fri, 10 Jun 2016 04:45:29 UTC All use subject to http://about.jstor.org/terms 494 TRANS. AMER. MICROSC. SOC., VOL. 87, NO. 4, OCT. 1968 ' . ' '-'.' '' ''- '.' S*.