‚Cejkaian tubules‘ in the posterior midgut of terrestrial Enchytraeidae (Oligochaeta)

Abstract

More than one hundred years ago, Bohumil Čejka described peculiar elongate tubules in the posterior region of the intestine of Hepatogaster birulae, a new terrestrial enchytraeid species collected in North-East Siberia. The tubules have no cilia but a proper epithelium and they run parallel to the longitudinal axis of the intestine over several segments, inside the intestinal epithelium but in close contact with the blood sinus. The tubules end blindly anteriorly and with a porus to the intestinal lumen posteriorly. The number of tubules increases from posterior to anterior due to bifurcations, and their diameter decreases. Čejka hypothesized that these tubules are glands that provide secretions for the final process of digestion or that aid in the egestion of faeces. He found them only in one species, Hepatogaster birulae, which was later synonymized with Henlea ochracea. In recent years we screened a large number of terrestrial enchytraeids in vivo and found these peculiar tubules in two further species of Henlea, in one species of Oconnorella and in thirteen species of Fridericia. The pores of these tubules are always located near the transition from midgut to hindgut. The tubules vary among species in extent and branching pattern, and several types can be distinguished. We suggest naming the structures ‘Cejkaian tubules’ in honour and memory of the finder, whose last publication dates from 1914. ‘Cejkaian tubules’ were not found in every species of Henlea and Fridericia, and they seem to be absent in other genera, but techniques other than in vivo light microscopy are required to confirm their absence with certainty. As to their function, we hypothesize the opposite of Čejka, not secretion but resorption, possibly of water, similar to the colon in tetrapod vertebrates.