Ultrastructural organisation of the spermatozoon of Allopodocotyle tunisiensis Derbel and Neifar, 2009 (Digenea, Opecoelidae), an intestinal parasite of Solea aegyptiaca Chabanaud, 1927 (Teleostei, Soleidae).

The ultrastructure of the spermatozoon of Allopodocotyle tunisiensis (Digenea, Opecoelidae), an intestinal parasite of Solea aegyptiaca (Teleostei, Soleidae), is described by transmission electron microscopy (TEM). The mature spermatozoon is a filiform cell that exhibits two axonemes of different length with the 9+'1' pattern of trepaxonematan Platyhelminthes. In the anterior spermatozoon extremity, cortical microtubules are absent. They appear after the disappearance of an anterior electron-dense material, being initially in a continuous and submembranous layer. They surround only partially the sperm cell. Later, these cortical microtubules are distributed into two bundles. Additionally, the spermatozoon of A. tunisiensis shows two mitochondria, a nucleus, an external ornamentation of the plasma membrane, spine-like bodies, and a large amount of glycogen granules. According to the location of the external ornamentation, A. tunisiensis presents a Quilichini et al.'s type 2 spermatozoon. With respect to the posterior extremity, the sperm cell of A. tunisiensis corresponds to the Quilichini et al.'s opecoelid type. The morphology of the first mitochondrion with a U-shaped posterior extremity is described for the first time in a digenean spermatozoon.

Ultrastructural study of the spermatozoon of Hemiurus appendiculatus (Digenea, Hemiuroidea, Hemiuridae), a parasite of Boops boops (Pisces, Teleostei, Sparidae) off Senegal.

The mature spermatozoon of Hemiurus appendiculatus exhibits the general pattern described in most of the digenean namely, two axonemes of the 9 + "1" pattern of the Trepaxonemata, a nucleus, a filiform mitochondrion, external ornamentations of the plasma membrane and parallel cortical microtubules located on one side of the spermatozoon. In this study, we show for the second time in a digenean spermatozoon the presence of microtubules of the second axoneme associated each in a short length with an external ornamentation, seven cortical microtubules, a terminal bulge in the anterior spermatozoon extremity separate from the remainder of the spermatozoon by a transverse constriction and the simultaneous presence of the external ornamentation of the plasma membrane with a filamentous ornamentation. The external ornamentations have a differentiated distribution, cover almost the anterior region of the spermatozoon, are more abundant around the first axoneme and extend backwards over a short distance around the second axoneme. This study also allowed us to reveal for the first time the existence in the Hemiuroidea of an axoneme that begins to disrupt before reaching the front end of the mitochondrion.

Ultrastructure and development of Nosema podocotyloidis n. sp. (Microsporidia), a hyperparasite of Podocotyloides magnatestis (Trematoda), a parasite of Parapristipoma octolineatum (Teleostei).

Nosema podocotyloidis n. sp. (Microsporidia, Nosematidae) is described from Podocotyloides magnatestis (Trematoda: Opecoelidae), a parasite of the fish Parapristipoma octolineatum (Teleostei) in the Atlantic Ocean. Electron microscopy reveals that all the stages of the cycle (merogony and sporogony) are diplokaryotic and in direct contact with the cytoplasm of host cells. There is no sporophorous vesicle (pansporoblast). The earliest stages observed are meronts, which have a simple plasmic membrane. Their cytoplasm is granular, rich in ribosomes and contains some sacculi of endoplasmic reticulum. They divide by binary fission into diplokaryotic sporonts. The sporonts have a thick electron-dense wall. Their diplokaryon is slightly less electron-dense than the cytoplasm. The cytoplasm of more advanced sporonts has numerous electron-lucent vesicles. Sporonts with two diplokarya divide by binary fission into diplokaryotic sporoblasts. The older sporoblasts are irregular or elongate and the polar filament is in formation. Their cytoplasm is denser, with ribosomes and lamellae of granular endoplasmic reticulum. The sporoblasts evolve into spores. The mature spores are broadly oval and measure 3.6 (3.1-4.0) × 2.58 (1.8-3.3) µm. Their wall is 100-300 nm thick. The polar tube is isofilar with 11-16 coils, 130-155 nm in diameter and arranged in many layers in the centre of the spore. The polaroplast is divided into two regions: an outer electron-dense cup with granular content and lacking lamellae and an internal region, less electron-dense, composed of irregularly arranged sacs. The posterior vacuole, with an amorphous electron-dense content, is present. The new species is compared with other species of Nosema from trematodes.

Ultrastructure of the spermatozoon of the digenean Lecithocladium excisum (Rudolphi, 1819) (Hemiuroidea: Hemiuridae), a parasite of marine teleosts in Senegal.

The present study describes the ultrastructure of the mature spermatozoon of Lecithocladium excisum (Rudolphi, 1819) (Digenea: Hemiuroidea: Hemiuridae) from the stomach of the marine teleost Scomber japonicus Houttuyn (Scombridae) captured in the Atlantic Ocean, off Dakar (Senegal). The ultrastructural organization of the spermatozoon of L. excisum follows the general model described in most digeneans. It presents two axonemes of the 9+'1' pattern of the Trepaxonemata, nucleus, mitochondrion and parallel cortical microtubules, among other characters. However, some particularities of the spermatozoon of L. excisum are (i) the presence of a membranous ornamentation not associated with cortical microtubules in its anterior extremity, (ii) the presence of a very reduced number of cortical microtubules located only in the ventral side of the spermatozoon and (iii) the absence of several structures described in most digeneans such as spine-like bodies and cytoplasmic expansions.