Fine structure of the uterus in tapeworm Tetrabothrius erostris (Cestoda: Tetrabothriidea).

The uterine organization in Tetrabothrius erostris (Tetrabothriidea) was investigated by the methods of transmission and scanning electron microscopy. In sexually mature proglottids, the uterine wall consists of a syncytial epithelium (1.4-2.5 μm thick, except in regions containing nuclei). The ribosomes, mitochondria and numerous cisternae of granular endoplasmic reticulum with concentric or parallel profiles with electron lucent material are observed in the epithelium. The uterine wall is characterized by the abundance of lipid droplets that are localized inside the long protrusions of the uterine epithelium (called fungiform papillae) up to 15-17 μm and in the surrounding medullary parenchyma. The protrusions with lipid droplets in the proximal ends of the uterus are located closely to each other. A basal matrix (up to 0.6 μm thick) supports the uterine epithelium. The musculature consisting of 1-2 muscle layers is well developed; large myocytons are connected with the myofibrils and have a nucleus that reaches 4 μm in size. In gravid proglottids, the epithelium without nuclei is reduced to 0.2-1.6 μm thick. The number of protrusions of the uterine epithelium and lipid droplets in the epithelial layer decreases. Sparse small muscle bundles underlay the uterine wall at this stage; the basal matrix is feebly marked. The matrotrophy or the support by nutrition from the parent organism to embryos is discussed for T. erostris which belongs to oligolecital cestodes and possesses numerous lipid droplets in the uterine wall during the development of embryos.