Microscopic anatomy and ultrastructure of the lophophoral organs and adjacent epithelia of the lophophoral concavity and the anal papilla of Phoronopsis harmeri Pixell, 1912 (Lophophorata: Phoronida)

Abstract

This paper describes the morphology and ultrastructure of lophophoral organs and adjacent epithelia of lophophoral concavity and anal papilla in the phoronid Phoronopsis harmeri. The lophophoral organ consists of two parts, which are connected to each other with a spacious foramen. The lower part is sack-shaped and the upper part is hood-shaped. Inside the lower part, there is a large cavity, which communicates to the environment with a narrow slit. Nephridiopores are directed towards these slits. Three types of lophophoral organ epithelia have been distinguished, all of them comprised supporting and glandular cells. Cells with inclusions resembling bacteria were found in the inner epithelium of lophophoral organs. The epithelium of the anal papilla consists of supporting and numerous glandular cells. The formation of spermatophores in lophophoral organs, as well as the structure and functions of glandular cells in epithelia of lophophoral organs and anal papilla, are discussed.