The Proboscis Hooks in Karkinorhynchidae and Gnathorhynchidae (Turbellaria, Kalyptorhynchia) as Basement Membrane or Intracellular Specializations

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Abstract
Doe, D. A. (Department of Zoology, University of North Carolina, Chapel Hill, North Carolina 27514, USA.) The proboscis hooks in Karkinorhynchidae and Gnathorhynchidae (Turbellaria, Kalyptorhynchia) as basement membrane or intracellular specializations. Zool. Scr. 5 (3–4): 105–115, 1976.—The fine structure analysis of the proboscis hooks in the genus Cheliplana Beauchamp revealed that these structures are specializations within the basement lamina enclosing the proboscis. The fine structure analysis of the proboscis hooks in the genus Gnatho‐rhynchus Meixner revealed that these structures are intracellular specializations within a fold of epithelium located at the junction of the proboscis sheath and proboscis cone. The electron dense hook material is deposited primarily in microvilli along the outer cell surface of the cone epithelium. The fine structural analysis of the unarmed proboscis in the genus Proschizorhynchus Meixner agrees with the description for the armed schizorhynchs and these findings support the view that the Schizorhynchia is a monophyletic group. The fine structural analysis of the unarmed proboscis in Florianella bipolaris Rieger & Sterrer agrees with the description for Gnathorhynchus. A comparison of the proboscis and hooks in the two kalyptorhynch suborders suggests a more distant relationship between them. A discussion of the methods for the anchorage of intracellular, intercellular and extracellular hard structures is also included.