Five new morphological types of virgulate and microcotylous xiphidiocercariae based on morphological and molecular phylogenetic analyses.

The phylogenetic position of most xiphidiocercariae from subgroups Cercariae virgulae and Cercariae microcotylae remains unknown or unclear, even at the family level. In this paper, we studied the morphology and molecular phylogeny of 15 microcotylous and virgulate cercariae (11 new and four previously described ones). Based on morphological and molecular data, we suggested five distinct morphological types of xiphidiocercariae, which are a practical alternative to Cercariae virgulae and Cercariae microcotylae subgroups. Four of these types correspond to actual digenean taxa (Microphallidae, Lecithodendriidae, Pleurogenidae and Prosthogonimidae), while the fifth is represented by Cercaria nigrospora Wergun, 1957, which we classified on the basis of molecular data for the first time. We reassessed the relative importance of morphological characters used for the classification of virgulate and microcotylous cercariae, and discussed the main evolutionary trends within xiphidiocercariae. Now stylet cercariae can be reliably placed into several sub-taxa of Microphalloidea on the basis of their morphological features.

Germinal elements and their development in Echinostoma caproni and Echinostoma paraensei (Trematoda) miracidia.

Among the large cells located in the posterior of Echinostoma caproni and E. paraensei miracidia are secretory cells, germinal cells (GC), and undifferentiated cells. Secretory cells do not give rise to progeny, whereas GC do. Undifferentiated cells develop into GC that can also divide to produce embryos. Cleavage of GC of E. caproni occurs only after the parasite has entered the snail host and develops into a sporocyst. With E. paraensei, GC are larger than noted for E. caproni, and in 3 of 23 miracidia examined, germinal cell cleavage had occurred in the miracidium such that an embryo containing 20-25 blastomeres was present. Observations on the germinal elements of miracidia help to explain previous results showing that (1) E. paraensei sporocysts release mother rediae a few days earlier than do sporocysts of E. caproni, and that (2) a single mother redia is produced ahead of all others by sporocysts of E. paraensei, but not by sporocysts of E. caproni. The present study adds support to the concept that E. caproni and E. paraensei are distinct species.

Migration and development of mother sporocysts of Echinostoma caproni (Digenea: Echinostomatidae).

Experimental infections of the mollusc Biomphalaria pfeifferi by Echinostoma caproni miracidia (Mi) were carried out in order to analyze the migration and development of mother sporocysts (MS) at 26 C. Miracidia penetrated different parts of the host's body, such as the mantle collar, the foot and head covering (including velum and tentacles), the mantle cavity, and the oral cavity. The ventricle and common aorta were the final sites of infection for the mother sporocysts after migration. The path of migration of the sporocyst was influenced by the point of MS penetration, but in all cases the MS reached the ventricle through the venous system. Developmental studies showed that newly hatched Mi contained 5-7 germinal cells (the primary germinal cells) and some undifferentiated cells. During sporocyst development, every primary germinal cell apparently gave rise to a redial embryo, whereas undifferentiated cells gave rise to both somatic and secondary generative cells. The eventual degeneration of the sporocyst seemed to cause the end of the development of this germinal material. The MS produced about 15 mother rediae (MR). Intramolluscan development of E. caproni MS consisted of 5 main periods: (1) resting, (2) migration, (3) growth, (4) reproduction, and (5) degeneration. A lower temperature of 21 C affected the duration of each stage. However, the path of sporocyst migration, the pattern of their growth, and the developmental steps of the germinal material were similar.