The Infraciliature and Argyrome of Opisthonecta henneguyi Faureé‐Fremiet

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Abstract
SYNOPSIS. Silver stains of the free‐swimming sessiline peritrich Opisthonecta henneguyi reveal the adoral infraciliature as the bases of two membranes, a haplokinety and a polykinety, which diverge at the buccal overture and spiral down the infundibulum to end at the cytostome. A second polykinety parallels the adoral polykinety in the oral half of the infundibulum, and the two form a peniculus. The haplokinety appears as a single row of kinetosomes, the adoral polykinety as a series of transverse rows of three kinetosomes. The peniculus is six kinetosomes in width.The electron microscope shows that the haplokinety is a double row of staggered kinetosomes. Only the external row bears cilia. The polykinety is a complex ciliary membrane, three kinetosomes wide. The three kinetosomes are connected with one another by fibrous bundles passing beneath them. They are linked orally and apically into longitudinal rows of thick, zig‐zag, fibrous connections. The kinetosomes of the internal longitudinal row are attached by a dense fiber to a strand of fibrous material interrupted at regular intervals by dense nodes.A section of the wall of the infundibulum is thrown up into longitudinal folds with tubular fibrils running parallel to the folds. These structures, the crests, appear to continue into the cytopharynx. Beneath and around the adoral and infundibular infraciliature and the crests is a fibrous matrix with dense nodes, resembling the reticulated infundibular fiber described by Faureé‐Fremiet.The trochal band in silver stains appears as short diagonal rows of kinetosomes. The electron microscope shows 5 to 7 kinetosomes per diagonal row. The kinetosomes of the diagonal rows are linked to thick dense rods which originate just above the trochal band and continue antapically past the kinetosomes for a distance of 10 to 15 μ. The kinetosomes are joined to one another by fibrous strands and each is also connected by a dense fiber to the diagonal rod to its left. Running below the kinetosomes and at right angles to the rods is a system of striated fibers.At the aboral end of the body, a ring, 2 μ in diameter, of argentophilic granules is shown by the electron microscope to be a small circle of kinetosomes. Sessile stages have not been reported for Opisthonecta. The aboral ring is probably a vestigial or non‐functioning scopula.The argyrome is represented by circular striae around the body. Each stria bears argentophilic dots on either its apical or its antapical side. Electron microscopy reveals that these dots are pores in the cuticle. The striae themselves may be points of adhesion between the inner cuticle and the outer cuticle, or ridges of cytoplasm between flattened alveoli of the inner cuticle. A dense fiber runs below and parallel to each stria.Opisthonecta shows at least three different kinds of ciliary membranes. Some speculations are offered on the taxonomic affinities of peritrichs based on their infraciliature.