The ultrastructure, function and morphogenesis of the tentacle in Discophrya sp. (suctorida) cileatea

Abstract

Tentacle structure, feeding and morphogenesis of the suctorian Discophrya sp. have been examined by light, scanning, and transmission electron microscopy. The long, slender mobile tentacles have an apical knob, which is covered only by the plasma membrane and contains haptocysts and clongate dense bodies. The tentacle shaft contains a central microtubular canal (axoneme) running from the base of the knob into the body cytoplasm, where it is surrounded by a unique fibrous collar. The axoneme is composed of two concentric rings of microtubules, the inner organized into curved lamellae. A short distance below the tip, the microtubules of the outer ring are joined by a connective sheath of limited length. Distal to this sheath, the axoneme is composed of helically arranged lamellae, the microtubules of which bear a restricted zone of inwardly pointing projections. Developmental stages of tentacle formation have been identified. New tentacle axonemes are formed in association with subcortical kinetosomes. During feeding the tentacle knob penetrates the prey ciliate body and is displaced laterally by the axoneme microtubules splaying outwards to form a funnel. The projections on the lamellae are thought to mediate the transport of the covering membrane and prey cytoplasm into the suctorian body. A number of possible mechanisms of tentacle movement and prey penetration are discussed.