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

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Abstract
Studies on anatomy and ultrastructure of the gutless tubificid P. leukodermatus (Oligochaeta, Annelida) revealed the complete absence of intestinal tissues. 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 studded with epicuticular projections. 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 worm''s body, numerous large, multivesiculate, membrane-bound corpuscles which lack typical cell organelles, fill the extra-epidermal subcuticular cavities. The bacteria, found in every specimen examined, probably 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.