Acta Parasitologica, Vol. 51, No. 3, 2006, 200-208 Aneta Yoneva(1)*, Katia Georgieva(1), Yana Mizinska(1), Boyko B. Georgiev(2,3) and Stoyanka R. Stoitsova(4) - Ultrastructure of spermiogenesis and mature spermatozoon of Skrjabinoporus merops (Cyclophyllidea, Metadilepididae)
(1)Institute of Experimental Pathology and Parasitology, Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 25, 1113 Sofia,
Bulgaria; (2)Central Laboratory of General Ecology, Bulgarian Academy of Sciences, 2 Gagarin Street, 1113 Sofia, Bulgaria;
(3)Departament of Zoology, Natural History Museum, Cromwell Road, London SW7 5BD, U.K.; (4)Institute of Microbiology,
Bulgarian Academy of Sciences, Acad. G. Bonchev Street, Block 26, 1113, Sofia, Bulgaria
*Corresponding author: ayoneva@iepp.bas.bg
ABSTRACT
The ultrastructure of the mature spermatozoon and the spermiogenesis of a cestode belonging to the family Metadilepididae
is described for the first time. The mature spermatozoon of Skrjabinoporus merops is characterized by twisted peripheral microtubules,
the presence of a single crested body, periaxonemal sheath and electron-dense rods, and the absence of intracytoplasmic
walls and inclusions (glycogen or proteinaceous granules); no peripheral microtubules where nucleus contacts the external
plasma membrane. Four morphologically distinct regions of the mature spermatozoon are differentiated. The proximal part
(Region I) contains a single crested body, periaxonemal sheath is absent in some (proximal) sections and is present in others
situated closer to the nucleus. The central Region II is nucleated, and is followed by Region III that contains a periaxonemal
sheath. The distal pole, Region IV, is characterized by disintegration of the axoneme. Spermiogenesis follows the type III pattern
(Ba and Marchand 1995) although in S. merops a slight flagellar rotation is observed. The differentiation zone is characterized
by the absence of striated roots and intercentriolar body; two centrioles are present, one of which gives rise to a free
flagellum. The latter rotates and undergoes proximodistal fusion with the cytoplasmic protrusion of the differentiation zone.
Spermiological characters of S. merops are similar to those of the families Taeniidae and Catenotaeniidae. The mature spermatozoon
differs from those of the Dilepididae (where the metadilepidid species have previously been classified) by the lack
of glycogen.
KEY WORDS: Cyclophyllidea, Metadilepididae, Skrjabinoporus merops, spermatozoon, spermiogenesis, ultrastructure