The Fine Structure of the Cyst Wall of the Ciliated Protozoon Didinium nasutum¹

Abstract

SYNOPSIS. Electron microscope observations of the complex cyst wall of Didinium nasutum are reported. The cyst wall is composed of 3 major coats. The outermost coat, the ectocyst, consists of short strands of filamentous material which forms a diffuse, amorphous layer approximately 8–9 μ thick. Culture debris, bacteria and unidentified inclusions have been observed adhering to the outer coat. The mesocyst, approximately 2.5 μ thick, has 2 distinct regions. The outer region is differentiated into several slightly thicker layers which in face view have a honeycomb appearance. The deeper region of the mesocyst consists of compact lamellae lacking the obvious honeycomb appearance of the layers of the outer region. Finally, the endocyst (0.3 μ thick), which arises in the mature cyst in the space that develops between the pellicle and the mesocyst, consists of delicate fibrils in a compact matrix. Both mesocyst and endocyst may be undulant and folded. The structure, origin and possible relationships of the various coats composing the cyst wall are discussed. The present study also contributes information on the role and fate of mucocysts and other cytoplasmic structures during the formation of the cyst wall.

Some Ultrastructural Observations on Encystment in Stylonychia mytilus (Ciliophora: Hypotrichida)

“…This is also the case in encysting Gastrostyla steinii. The lamellar structure is similar to that noted for the inner mesocyst of the gymnostome Didinium nasutum (Holt & Chapman, 1971). It appears that the "herringbone" structure of the mesocyst is a transition state for the predominantly lamellar mesocyst found in resting cysts and may represent an incomplete packing of the fibers.…”

“…Thus, both of these protozoan species can probably be eliminated as paralytic shellfish causative agents in Southeast Alaska. Mesodinium rubrum from the Atlantic has also been described as nontoxic (Anonymous, 1968 Protozoan encystment requires considerable dedifferentiation-both physiologically (Pigon, 1959) and morphologically (Grimes, 1973;Hashimoto, 1962Hashimoto, , 1963Holt & Chapman, 1971;Kink, 1973;Tibbs, 1969 All use subject to JSTOR Terms and Conditions cytoplasmic reserves, increase in density of the cytoplasm due to intense dehydration, and a concomitant decrease in cellular volume have all been noted as characteristic of the phenomenon. Recently, a thorough study of the encystment and excystment of the hypotrich Oxytricha fallax showed that this ciliate undergoes a number of striking morphological changes (Grimes, 1973).…”

“…Protozoan encystment requires considerable dedifferentiation-both physiologically (Pigon, 1959) and morphologically (Grimes, 1973;Hashimoto, 1962Hashimoto, , 1963Holt & Chapman, 1971;Kink, 1973;Tibbs, 1969). The accumulation of 1 The red pigment may be released after centrifugation.…”

Comments on the Role of the Cyst in the Life Cycle and Survival of Free-Living Protozoa

“…Some of the information obtained thus far indicates that mucocysts may be involved in the formation of the thin cystic membrane of the reproductive cyst of Tetrahymena rostrata (see Zebrun et al, 1967). Holt & Chapman (1971) reported that in Didinium other structures, which they call clathrocysts, are-in addition to mucocysts-involved in the formation of at least one of the cyst wall layers. Kawakami & Yagiu (1963a, b; 1964a-c) offer ultrastructural details concerning the cystic membranes of Colpoda.…”

Identifikation von Merozoiten der vier cystenbildenden Coccidien (Sarcocystis, Toxoplasma, Besnoitia, Frenkelia) auf Grund feinstruktureller Kriterien

“…Eine kleinere Anzahl ist ,,sph/irisch und yon ziemlich gleiehbleibender GrSl~e", n~mlieh 6--7 ~m. ,,Zwischen diesen beiden Formen finden sich die mannigfaltigsten Uberg/~nge, welche nieht zweifeln lassen, daI~ die einen, ns die nierenfSrmigen, eine h6here Ausbildung der anderen sind" (Miescher, 1843 (Ludvik, 1960) und bei S./usiformis (Simpson, 1966) Kattar, 1969;Grain, Golinska, 1969;Holt, Chapman, 1971 …”