Ultrastructural study of the proboscis of Malacobdella grossa (Nemertea: Hoplonemertea)

Abstract

The proboscis of the symbiotic nemertean Malacobdella grossa was examined with transmission electron microscopy to reveal more features of bdellonemerteans for phylogenetic analysis. General morphology of the proboscis of Malacobdella corresponds to that of a typical hoplonemertean: the middle chamber is present; the nervous system of the proboscis is embedded in the connective tissue between the inner and outer longitudinal muscle layers; the radially arranged nerve trunks are clearly seen over a considerable portion of their extent. Unique features (i.e. autapomorphies) of Malacobdella’s proboscis include: interwoven longitudinal muscle fibres; nerve plexus in the anterior part of the proboscis; absence of mucus glands; presence of subepithelial glands; reduced musculature in the middle chamber; and absence of glandular epithelium in the posterior chamber.

Keywords:

• hoplonemertea
• Malacobdella
• proboscis
• ultrastructure

Acknowledgements

We thank Mrs Nataliya Miroshnikova for correcting the English text. We are also grateful to Dr Svetlana A. Maslakova and an anonymous reviewer for helpful comments on the manuscript. The study was supported by the grant 10-04-00570 from the Russian Foundation for Basic Research.