Scanning Electron Microscopy of the Adoral Ciliary Zone of Entodinium Stein (Ciliophora, Entodiniomorphida)

Abstract

The adoral ciliary zone of the rumen ciliates, Entodinium spp., was observed topographically in the SEM. The upper side of the anterior end of the body was indented by the vestibulum, which had cilia arranged on its right wall and ribs along the left wall. The adoral ciliary zone could be divided into at least two arrangements. The outer ciliary zone had many membranelle‐like structures, which consisted of cilia arranged radially from the body axis. Each membranelle‐like structure consisted of two rows of about eight cilia each lining up in a single file. It was, however, different from a typical membranelle, because its cilia were connected with the vestibular cilia and were arranged not spirally but on a plane. These cilia extended toward the outside because of the projecting cytoplasm from which they originated. In contrast, the cilia of the inner ciliary zone were aggregated to form relatively unsystematic bundles. Since the vestibular opening was slanted on the upper side of the body, the ciliary bundles were thick on the lower side and sparse on the upper side of the body. Neither outer nor inner ciliary zones completely surrounded the vestibular opening. The ciliature started from the left side of the vestibular opening, encircled the lower side of the body, and entered the vestibulum from its right side. The functions of these two types of ciliary arrangements are discussed.

Scanning Electron Microscopy of the Adoral Ciliary Zone of Entodinium Stein (Ciliophora, Entodiniomorphida)

“…The present observations revealed that not only the bases of cilia in the outer and inner adoral zones were arranged uniformly as indicated by former investigators ( 2 , 1 3 , but also that the cilia of the outer adoral zone were aggregated to form ciliary tufts in contrast with the cilia of the inner zone, which had a random arrangement. Such an arrangement of cilia of the adoral zone closely resembles that of Entodinium (7), which is classified as an entodiniomorphid ciliate like Cycloposthiurn. Nevertheless, despite the similarities in the inner zone, differences exist between both genera.…”

“…packed cilia arising from a packet of kinetosomes (1). Previously, we reported that species of Entodinium, one of the entodiniomorphid genera inhabiting the rumen, have two types of ciliary zones on the peristome and suggested that these respective ciliary zones would play useful roles for movement and ingestion of food (7). The present paper describes the adoral ciliary zone of other entodiniomorphids, Cycloposthium spp., commonly inhabiting the large intestine of the horse.…”

“…Other differences between the two genera are that the vestibulum in Cycloposthium has no cilia but is ciliated in Entodinium; the vestibular opening is located at the center to right side of the anterior end of the body in Cycloposthium but at the upper side in Entodinium. Finally, Cycloposthium possesses a fairly large horseshoe-like operculum without cilia at the center of the adoral ciliary zone while Entodinium has only a small arc-shaped area without cilia (7).…”

“…rows of about eight cilia each (7) though their infraciliature shows no corresponding differences (5). In addition, the outer and inner adoral zones are separated by a narrow band without cilia in Cycloposthium, but not in Entodinium (3, 7,15). Other differences between the two genera are that the vestibulum in Cycloposthium has no cilia but is ciliated in Entodinium; the vestibular opening is located at the center to right side of the anterior end of the body in Cycloposthium but at the upper side in Entodinium.…”

In Memoriam: Soichi Imai (1948–2015)

“…His first studies were observations on the adoral ciliary zone by scanning electron microscopy (Imai et al. , ). He continued these studies by refined silver impregnation (Ito and Imai ,b, , ; Ito et al.…”