Spermatological characters of bothriocephalideans (Cestoda) inferred from an ultrastructural study on Oncodiscus sauridae and Senga sp

New data on spermiogenesis and trepaxonematan axoneme in basal tapeworms (Cestoda, Caryophyllidea, Lytocestidae) parasitizing cyprinid fishes

Monozoic caryophyllidean cestodes, intestinal parasites of cyprinid fishes, represent a group of tapeworms with an unclear evolutionary history. As spermatology may provide phylogenetically important data, the spermiogenesis and ultrastructure of the mature spermatozoon have been investigated using an integrative approach combining transmission electron microscopy, cytochemistry and electron tomography in Khawia rossittensis (Szidat, 1937). The process of spermatid formation is accompanied by the presence of ultrastructural characters not described in traditional models of spermiogenesis, e.g., apical electron-dense material, the two striated roots situated unusually opposite each other, branching of typical striated roots, an intercentriolar body comprising five electron-dense and four electron-lucent layers, rotation of both free flagella and flagellar buds to the median cytoplasmic process at 90°, and a complete proximodistal fusion. The synchronous rotation of both flagellar buds and growing free flagella is an evolutionarily linked pattern favouring the hypothesis that the Caryophyllidea are not ancestral but are secondarily derived from polyzoic forms. Electron tomography analysis has revealed a unique feature of two helicoidal tubular structures in the central electron-dense core of the axoneme of mature spermatozoon. These data provide new insights into the architecture of the 9 + '1' axoneme, which is shared by male gametes of all trepaxonematan Platyhelminthes.

First ultrastructural and cytochemical data on the spermatozoon and its differentiation in progenetic and adult Archigetes sieboldi Leuckart, 1878 (Cestoda, Caryophyllidea, Caryophyllaeidae)

Spermiogenesis in progenetic and adult stages of Archigetes sieboldi Leuckart, 1878, a tapeworm parasitic in oligochaetes and fish respectively, has been examined using transmission electron microscopy and cytochemical staining for glycogen. General pattern of spermiogenesis is essentially like that of other caryophyllideans, i.e., apical dense material in the zone of differentiation in the early stages of spermiogenesis, rotation of free flagellum and a flagellar bud, and proximo-distal fusion. Interestingly, rotation of a free flagellum and flagellar bud to the median cytoplasmic process (MCP) has been observed unconventionally at > 90° only in progenetic stages. Typical striated roots associated with the centrioles occur rarely in A. sieboldi, and only in form of faint structures in advanced stages of spermiogenesis. In contrast to most caryophyllideans studied to date, penetration of the nucleus into the spermatid body has started before the fusion of the free flagellum with the MCP. This feature has been reported rarely but exclusively in the family Caryophyllaeidae. The unipartite mature spermatozoon of A. sieboldi is composed of one axoneme of the 9 + '1' trepaxonematan pattern with its centriole, parallel nucleus, and parallel cortical microtubules which are situated in a moderately electron-dense cytoplasm with glycogen particles. An unusual arrangement of cortical microtubules in the two parallel rows in region I of the spermatozoon is described here for the first time in the Caryophyllidea. Ultrastructural data on spermiogenesis and the spermatozoon in A. sieboldi from tubuficids and carp are compared and discussed with those in other caryophyllideans and/or Neodermata.

Spermatozoon cytoarchitecture of Amphilina foliacea (Platyhelminthes, Amphilinidea)

The mature spermatozoon of Amphilina foliacea Rudolphi, 1819 has been examined using transmission electron microscopy. The male gamete is filiform and tapered at both extremities. Its moderately electron-dense cytoplasm possesses two parallel axonemes of unequal lengths with the 9 + "1" trepaxonematan pattern, a mitochondrion, a nucleus, parallel cortical microtubules, four electron-dense attachment zones, and electron-dense glycogen granules. A crested body is absent. The anterior extremity of the cell exhibits a single axoneme. The anteriormost cortical microtubules have been observed with the appearance of the second axoneme. The number of cortical microtubules reaches a maximum (up to 25) in the nucleated region III of the spermatozoon. A single mitochondrion extends from the middle of region II to the end of region III of the cell. Both axonemes have become disorganized in a similar way: the axonemal doublets disappear first, followed by the central core. The nucleus is surrounded by a few cortical microtubules in the proximal part of region V. In the distal extremity of the mature spermatozoon, there is only the nucleus. Differences of spermatozoon ultrastructure within Amphilinidea and other Neodermata are discussed.

Ultrastructural study of the male gamete of Glossobothrium sp. (Cestoda: Bothriocephalidea: Triaenophoridae) a parasite of Schedophilus velaini (Perciformes: Centrolophidae) in Senegal

This paper describes the ultrastructure of the male gamete of Glossobothrium sp. (Bothriocephalidea: Triaenophoridae). The mature spermatozoon of Glossobothrium sp. is filiform and possesses two axonemes, a single helicoidal crested body, a parallel nucleus, parallel cortical microtubules and granules of glycogen. In Glossobothrium sp. we describe for first time a 200-250 nm thick crest-like body in the Bothriocephalidean. The anterior part of the spermatozoon exhibits a ring of 27 electron-dense cortical microtubules encircling the first axoneme. This structure persists until the appearance of the second axoneme. When the ring of electron-dense cortical microtubules disappears, the spermatozoon exhibits two bundles of thin cortical microtubules. The posterior part of the spermatozoon contains the posterior extremity of the second axoneme, the posterior extremity of the nucleus and few cortical microtubules. Soon nucleus disappears and the axoneme is disorganized. Thus the posterior extremity of the spermatozoon of Glossobothrium sp. exhibits only singlets produced by the disorganization of the doublets of the second axoneme and few cortical microtubules. This type of posterior extremity of the mature spermatozoon has never been described previously in the Triaenophoridae.

Ultrastructure of the spermatozoon of the diphyllobothriidean cestode Cephalochlamys namaquensis (Cohn, 1906)

This contribution provides the first ultrastructural and cytochemical data on the mature spermatozoon of a diphyllobothriidean cestode belonging to the family Cephalochlamydidae. The mature spermatozoon of Cephalochlamys namaquensis (Cohn, 1906), a parasite of the African clawed frog, Xenopus laevis (Daudin, 1802), from southern California, USA, has been examined using transmission electron microscopy and cytochemical staining with periodic acid-thiosemicarbazide-silver proteinate for glycogen. The male gamete is a filiform cell tapered at both extremities. Its moderately electron-dense cytoplasm possesses two parallel axonemes of unequal lengths with a 9 + "1" trepaxonematan pattern, a nucleus, parallel cortical microtubules, four electron-dense plaques/attachment zones, and electron-dense granules of glycogen. The crested body is absent. The anterior extremity of the cell exhibits a centriole surrounded by a semiarc of four parallel cortical microtubules. The number of cortical microtubules reaches its maximum (up to 37) at the beginning of the anucleated two-axoneme region II of the spermatozoon. In contrast to other diphyllobothriideans, a small membranous element appears in the anucleated region II. In addition, the nucleus is surrounded by a few cortical microtubules in region V. The distal extremity of the mature spermatozoon exhibits only one nucleus. Variations of spermatozoa ultrastructural characters within diphyllobothriideans as well as other Eucestoda are discussed.

Ultrastructure of the spermatozoon of Bothriocotyle sp. (Cestoda: Bothriocephalidea), a parasite of Schedophilus velaini (Sauvage, 1879) (Perciformes: Centrolophidae) in Senegal

The mature spermatozoon of Bothriocotyle sp. is filiform and tapered at both extremities. It possesses 2 axonemes of unequal length, showing the 9 + "1" pattern of Trepaxonemata. The anterior extremity exhibits a crest-like body. Thereafter, the crest-like body disappears, and the first axoneme is surrounded by a ring of cortical microtubules (about 27 units) that persist until the appearance of the second axoneme. This ring of cortical microtubules is characteristic only for species of Bothriocephalidea and represents a very useful phylogenetic character. The spermatozoon cytoplasm is slightly electron-dense and contains numerous electron-dense granules of glycogen in several regions. The anterior and posterior extremities of the spermatozoon lack cortical microtubules. The posterior extremity of the spermatozoon of Bothriocotyle sp. possesses a nucleus and a disorganized axoneme, which also characterizes spermatozoa of the Echinophallidae studied to date.

Spermatological characters of monozoic tapeworms (Cestoda: Caryophyllidea), including first data on a species from the Indomalayan catfish

The ultrastructure of spermiogenesis and mature spermatozoon in Lytocestus indicus (Cestoda: Lytocestidae) is described; this is the first representative of this group of monozoic, presumably most basal, tapeworms (Eucestoda) from the Indomalayan region to be documented in this manner. Similarly, as in other caryophyllideans, its spermiogenesis involves the formation of a conical differentiation zone with 2 centrioles associated with striated roots and an intercentriolar body. In the course of the process, 1 of the centrioles develops a free flagellum, which fuses with a cytoplasmic protrusion, whereas the other remains oriented in a cytoplasmic bud. Spermiogenesis is also characterized by the presence of electron-dense material in the early stages of spermiogenesis and a slight rotation of the flagellar bud. The mature spermatozoon of L. indicus is a filiform cell tapered at both extremities that lacks mitochondria; its nucleus has parallel disposition to the axoneme and does not reach up to the posterior extremity of the spermatozoon, which is typical for spermatozoa of the type III pattern. The new data confirm that caryophyllideans share the same type of spermiogenesis that is considered to be plesiomorphic in the Eucestoda. The existing information on spermatological ultrastructure of 8 members for 3 of 4 caryophyllidean families from different host groups (cyprinids and catostomids, both Cypriniformes, and mochokids and clariids, both Siluriformes) from 4 zoogeographical regions (Palearctic, Neotropic, Ethiopian, and Indomalayan regions) demonstrates great uniformity in spermiogenesis and sperm ultrastructure, which does not reflect different taxonomic position of the species studied.

Spermiogenesis and spermatozoon ultrastructure of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost fish Merluccius merluccius (Gadiformes: Merlucciidae)

Spermiogenesis and the ultrastructure of the spermatozoon of the bothriocephalidean cestode Clestobothrium crassiceps (Rudolphi, 1819), a parasite of the teleost fish Merluccius merluccius (Linnaeus, 1758), have been studied by means of transmission electron microscopy. Spermiogenesis involves firstly the formation of a differentiation zone. It is characterized by the presence of two centrioles associated with striated rootlets, an intercentriolar body and an electron-dense material in the apical region of this zone. Later, two flagella develop from the centrioles, growing orthogonally in relation to the median cytoplasmic process. Flagella then undergo a rotation of 90° until they become parallel to the median cytoplasmic process, followed by the proximodistal fusion of the flagella with the median cytoplasmic process. The nucleus elongates and afterwards it migrates along the spermatid body. Spermiogenesis finishes with the appearance of the apical cone surrounded by the single helical crested body at the base of the spermatid. Finally, the narrowing of the ring of arched membranes detaches the fully formed spermatozoon. The mature spermatozoon of C. crassiceps is filiform and contains two axonemes of the 9 + "1" trepaxonematan pattern, a parallel nucleus, parallel cortical microtubules, and electron-dense granules of glycogen. The anterior extremity of the gamete exhibits a short electron-dense apical cone and one crested body, which turns once around the sperm cell. The first axoneme is surrounded by a ring of thick cortical microtubules that persist until the appearance of the second axoneme. Later, these thick cortical microtubules disappear and thus, the mature spermatozoon exhibits two bundles of thin cortical microtubules. The posterior extremity of the male gamete presents only the nucleus. Results are discussed and compared particularly with the available ultrastructural data on the former "pseudophyllideans". Two differences can be established between spermatozoa of Bothriocephalidea and Diphyllobothriidea, the type of spermatozoon (II vs I) and the presence/absence of the ring of cortical microtubules.

Spermatological characters of Acanthobothrium crassicolle Wedl, 1855 (Tetraphyllidea, Onchobothriidae), a parasite of the common stingray Dasyatis pastinaca

We describe the spermiogenesis process and the ultrastructural characters of the spermatozoon of Acanthobothrium crassicolle by means of transmission electron microscopy, including cytochemical analysis for glycogen. Spermiogenesis in A. crassicolle begins with the formation of the differentiation zone that contains two centrioles associated with striated rootlets and an intercentriolar body. The latter is formed by one electron-dense layer. The centrioles develop into two free flagella that first grow orthogonally to a median cytoplasmic process and then undergo flagellar rotation becoming parallel to that median cytoplasmic process. After flagellar rotation only one of the flagella completes its growth and both short and long flagella undergo proximodistal fusion with the median cytoplasmic process. In the final stages of spermiogenesis, the nucleus becomes filiform and migrates into the spermatid body. Later, the ring of arched membranes constricts and the spermatozoon is liberated from the residual cytoplasm. The ultrastructural organization of the spermatozoon of A. crassicolle follows the general pattern of spermatozoa of the other Tetraphyllidea-Onchobothriidae species, but exhibits some differences. It is filiform, tapered at both extremities and lacks mitochondrion. It contains two axonemes of unequal length showing the 9 + “1“ pattern of Trepaxonemata, a nucleus, parallel cortical microtubules and electron-dense granules of glycogen. The anterior extremity of the male gamete contains a single crested body surrounding a thin and long apical cone. This type of apical cone has never been described in a tetraphyllidean spermatozoon. Another particularity is the presence of a single electron-dense microtubule at the vertex of the crested body.