The Gutless Marine Oligochaete Phallodrilus leukodermatus. Structural Studies on an Aberrant Tubificid Associated with Bacteria

Abstract

Studies on anatomy and ultrastructure of the gutless tubificid Phallodrilus leukodermatus (Oligochaeta, Annelida) revealed the complete absence of intestinal tissues. However the wide, septate coelomic cavity is traversed by alveolate (mesodermal?) cells between which are embedded few longitudinal or oblique muscle strands and some blood vessels. The much wrinkled cuticle is densely stud with 'epicuticular projections' (Richards, 1977). In a space system between epidermis and cuticle, particularly wide in the postclitellar region, many gram-negative, rod-shaped bacteria are found. In the posterior part of the worms' body numerous large, multivesiculate, membrane-bound corpuscles which lack typical cell organelles, fill the extra-epidermal subcuticular cavities. It is speculated that the bacteria, found in every specimen examined, are of nutritional significance for the worms. The aberrant anatomy of the tubificids, their association with procaryotes and parallels to other gutless marine animals are discussed.