Acta Parasitologica, Vol. 50, No. 2, 2005, 124-131 Daniel Mlocicki(1)*, Zdzislaw Swiderski(1,2), David Bruce Conn(3), Catarina Eira(4), Jordi Miquel(4)
and Anna Baranowska-Korczyc(5) - Ultrastructure of oncospheral hook formation in the cestode Mosgovoyia ctenoides (Railliet, 1890) Beveridge, 1978 (Cyclophyllidea, Anoplocephalidae)
(1)W. Stefanski Institute of Parasitology, Polish Academy of Sciences, 51/55 Twarda Str., 00-818 Warsaw; (2)Department of General Biology and Parasitology, Warsaw Medical University, 5 Chalubinskiego Str., 02-004 Warsaw, Poland; (3)School of Mathematical and Natural
Sciences, Berry College, Mount Berry, Georgia 30149-5036, USA; (4)Laboratori de Parasitologia, Facultat de Farmacia, Universitat de
Barcelona, Av. Joan XXIII s/n, E-08028 Barcelona, Spain; (5)Department of Medical Biology, Warsaw Medical University,
73 Nowogrodzka Str., 02-018 Warsaw, Poland
*Corresponding author: danmlo@twarda.pan.pl
ABSTRACT
The ultrastructure of oncospheral hook formation in the anoplocephalid cestode Mosgovoyia ctenoides (Railliet, 1890) Beveridge, 1978, is described. The hook morphogenesis takes place inside the six symmetrically arranged hook-forming cells,
the oncoblasts. They show characteristic large nuclei of semilunar shape, localized at one pole of the embryo. At the beginning
of the hook formation, the "hook-forming centre" appears in the cytoplasmic part of each oncoblast. It consists of numerous
free ribosomes and polyribosomes surrounded by several mitochondria and Golgi complexes. The hook-forming centre is
involved in synthesis of an electron-dense, undifferentiated hook primordium, which undergoes progressive differentiation
and elongation into the fully developed hook. A fully formed oncospheral hook consists of the three parts: blade, shank, and
base. Each hook, at the site of its protrusion from the oncosphere, is surrounded by two electron-dense rings interconnected
by a circular septate junction. The hook material consists of two or three layers that differ in electron density: (1) a moderately
electron-dense core, (2) a middle layer of low electron density, and (3) a highly osmiophilic cortex. Wide bands of hook
muscles are attached to the basal and collar parts of the hook. The hook blades project outside of the oncospheral body into a
large cavity delimited by the hook region membrane attached at this pole directly to the oncospheral surface. In the fully developed
oncosphere of M. ctenoides, the three pairs of oncospheral hooks and their muscles form a complex "hook muscle system",
responsible for coordinated hook action. The differentiation and ultrastructure of oncospheral hooks in the oncospheres of
M. ctenoides are compared to those described in other cestode species.
KEY WORDS: Mosgovoyia ctenoides, Cestoda, Cyclophyllidea, Anoplocephalidae, ultrastructure, oncospheral hook, oncoblast