Ultrastructural evidence for completion of the entire miracidial maturation in intrauterine eggs of the digenean Brandesia turgida (Brandes, 1888) (Plagiorchiida: Pleurogenidae)

Zdzisław Świderski,David Bruce Conn,Aleksander E Zhokhov,Jordi Miquel,Larisa G Poddubnaya

doi:10.1007/s00436-013-3747-y

Abstract

Results of this TEM study provide ultrastructural evidence that miracidial morphogenesis is fully completed within the intrauterine eggs situated in the most posterior uterine regions of the pleurogenid trematode Brandesia turgida (Brandes, 1888). The ultrastructural characteristic of different larval organelles and cell types of these eggshell-enclosed, but fully formed, cilated miracidia is described. The body wall of the pyriform mature miracidium of B. turgida is composed of ciliated epidermis and underlying peripheral body musculature. Two miracidial flame cells of the protonephridial excretory system are localized in the central region of the ciliated larvae. Three types of miracidial glands were observed: a single apical gland, two lateral glands, and several small vesiculated glands; each gland type contains characteristic, but different types of secretory granules. The anterior end of each miracidium consists of an apical papilla on which are situated the exits of the three main larval glands: an exit of a single apical gland as well as the individual exits of two lateral glands. The exits of vesiculated glands, containing characteristic spherical membrane-bound and highly electron-dense granules, evidently different from the two other types of secretory granules of apical and lateral glands, were not identified. Germinative cells, grouped together in a sac-like germinative follicle, are situated in the medioposterior part of the larva, the germatophore. The germinative cells contain numerous electron-dense heterochromatin islands arranged in the form of a network or chain-like pattern and distributed mainly in the karyoplasm adjacent to the nuclear membrane. The thin layer of granular cytoplasm is rich in free ribosomes and contains a few small mitochondria. Both nuclear and cytoplasmic features if these cells indicate their great developmental potential for further growth and multiplication in postembryonic stages of the life cycle. In the mature eggs, the areas of focal cytoplasmic degradation were frequently observed and may be involved in the autolysis of some embryonic structures. Obtained results are compared with available literature data on the functional ultrastructure of the miracidia of other digeneans.

Highlights

To our knowledge, there are no published data on the ultrastructure of the intrauterine, eggshell-enclosed mature miracidia of digenean trematodes examined by means of transmissionParasitol Res (2014) 113:1103–1111 electron microscopy (TEM)
The miracidia enclosed in the intrauterine eggs of B. turgida show the presence of almost all of the larval organelles and
Three types of miracidial glands were observed in these ciliated larvae: a single apical gland (Figs. 2 and 3), two lateral glands (Figs. 2 and 3a) and several small vesiculated glands (Fig. 4); Fig. 3 (a) Peripheral part of the eggshell-enclosed (ES) miracidium showing two large nuclei (N) of the tegumental perikarya (STP) with numerous heterochromatin islands (HCh) of irregular shapes, frequently adjacent to the nuclear envelope

Summary

Introduction

There are no published data on the ultrastructure of the intrauterine, eggshell-enclosed mature miracidia of digenean trematodes examined by means of transmissionParasitol Res (2014) 113:1103–1111 electron microscopy (TEM). There are no published data on the ultrastructure of the intrauterine, eggshell-enclosed mature miracidia of digenean trematodes examined by means of transmission. Little TEM information is available on the hatched, free-swimming miracidia of different digenean species. More frequent are the scanning electron microscope (SEM) studies on the hatched, free-swimming miracidia of different digenean species (Eklu-Natey et al 1981, 1985). The aim of the present study is twofold: (1) to provide ultrastructural evidence for completion of the entire miracidial maturation in the intrauterine eggs of the pleurogenid digenean Brandesia turgida and (2) to describe the ultrastructure of these eggshell-enclosed, fully formed, ciliated miracidia of this trematode, a common parasite of the marsh frog Pelophylax ridibundus (Pallas, 1771), previously known as Rana ridibunda, in Europe. Our previous study on the eggs of this digenean species was focused only on the ultrastructure of the egg wall surrounding the miracidium, with the description of a unique cocoon-like envelope (Świderski et al 2013a)

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