An Ultrastructural Study of the Distal Epidermis and the Occurrence of Subcuticular Bacteria in the Gutless Tubificid Phallodrilus Albidus (Oligochaeta:Annelida).

Abstract

The typically annelid cuticle of Phallodrilus albidus has an increased population density of epicuticular projections, but this is not thought to be related to its gutless condition. The irregular outline of the apical membrane of the epidermal cells is an inherent feature, possibly enhancing an absorptive function. The cuticle-epidermal interface is characterized by multigranular bodies, rod-shaped bacteria and filiform structures. The multigranular bodies are present in the postclitellar region only, coinciding with the chalkiness of living specimens. The bacteria occur throughout the entire length of the worm, their presence exaggerating the irregularities of the apical membrane. The bacterial cytoplasmic membrane, in contrast to the limiting membrane, was difficult to resolve. Between the two membranes is an amorphous zone. Storage granules of a carbohydrate-rich complex are located peripherally and the bacterial core contains a reticulum of DNA threads. Filiform structures, ultrastructurally similar to the bacterial peripheral region, are numerous, especially where the bacteria are carbohydrate-rich. Connections with the bacterial bodies were observed, but infrequently. The non-pathologic association between the subcuticular bacteria and the gutless tubificid is discussed.