A microtubule organizing centre (MTOC) is responsible for the production of the sperm flagellum in Matsucoccus feytaudi (Hemiptera: Coccoidea)

A microtubule organizing centre (MTOC) has been described in the spermatid of the hemipteran Matsucoccus feytaudi (Coccoidea). This structure, revealed as a fluorescent ring by treatment with γ-tubulin antibody, gives rise to a bundle of microtubules which surrounds the elongated cylindrical nucleus. This microtubule bundle has been considered an atypical sperm flagellum provided with sperm motility. A comparison of the M. feytaudi MTOC with the material associated with the centriole of Drosophila melanogaster spermatids confirms the great similarity between the two structures, both involved in the nucleation of microtubules. Like the D. melanogaster material associated with the centriole, the M. feytaudi MTOC is a transient structure which disappears or degenerates at the end of spermiogenesis and is no longer visible in the mature sperm.     

The sperm of Matsucoccus feytaudi (Insecta,Coccoidea): Can the microtubular bundle be considered as a true flagellum?

In the present work the spermiogenesis and sperm structure of Matsucoccus feytaudi, a primary pest of the maritime pine in southern eastern Europe, is studied. In addition to the already known characteristics of coccid sperm, such as the absence of the acrosome and mitochondria, and the presence of a bundle of microtubules responsible for sperm motility, a peculiar structure from which the microtubule bundle takes origin is described. Such a structure – a short cylinder provided with a central hub surrounded by several microtubules with a dense wall – is regarded as a Microtubule Organizing Centre (MTOC). During spermiogenesis, quartets of fused spermatids are formed; from each spermatid, a bundle of microtubules, generated by the MTOC, projects from the cell surface. Each cell has two centrioles, suggesting the lack of a meiotic process and the occurrence of parthenogenesis. At the end of the spermiogenesis, when the cysts containing bundles of sperm are formed, part of the nuclear material together with the MTOC structure is eliminated. Based on the origin of the microtubular bundle from the MTOC, the nature of the bundle as a flagellum is discussed.     

The spermatogenesis and the sperm structure of Terebrantia (Thysanoptera, Insecta)

Spermatogenesis and the sperm structure of the terebrantian Aeolothrips intermedius Bagnall are described. Spermatogenesis consists of two mitotic divisions; the second is characterized by the loss of half of the spermatids, which have pyknotic nuclei. Early spermatids have two centrioles, but when spermiogenesis starts, a third centriole is produced. The three basal bodies give rise to three flagella; later these fuse into a single flagellum which contains three 9 + 0 axonemes. The basal bodies are surrounded by a large amount of centriole adjunct material. During spermiogenesis this material contributes to the shifting of the three axonemes towards the anterior sperm region parallel to the elongating nucleus, and it is transformed into a dense cylinder. In the mature spermatids the three axonemes amalgamate to create a bundle of 27 doublet microtubules. Near the end of spermiogenesis the dense cylinder of the centriole adjunct lies parallel to the nucleus and the axonemes. It ends where the mitochondrion appears at half-sperm length. We confirm that Terebrantia testes have a single sperm cyst; their sperm are characterized by a cylindrical nucleus, three axonemes fused into one, a small mitochondrion and a short cylindrical centriole adjunct which corresponds to the dense body described in a previous work. The acrosome is lacking. At the midpoint of the anterior half of the sperm the outline of the cross-section is bilobed, with the nucleus contained in a pocket evagination of the plasma membrane. These characters are discussed in light of a comparison between Tubulifera and Terebrantia.     

Spermiogenesis in Polyplacophora,with special reference to acrosome formation (Mollusca)

Summary The present study examines spermiogenesis, and in particular the formation of the acrosome, in ten species of chitons belonging to four families. This study emphasizes the formation of the acrosome but brings to light several other structures that have received little or no mention in previous studies. The process of spermiogenesis is essentially similar in each species, although Chaetopleura exhibits some significant differences. In early spermiogenesis the Golgi body secretes numerous small pro-acrosomal vesicles that gradually migrate into the apical cytoplasm. The chromatin condenses from granules into fibres which become twisted within the nucleus. A small bundle of chromatin fibres projects from the main nuclear mass into the anterior filament; this coincides with the appearance of a developing manchette of microtubules around the nucleus that originates from the two centrioles. Radiating from the distal centriole is the centriolar satellite complex, which is attached to the plasma membrane by the annulus. The distal centriole produces the flagellum posteriorly and it exits eccentrically through a ring of folded membrane that houses the annulus. Extending from the annulus on one side of the flagellum, in all but one species, is a dense fibrous body that has not been previously reported. The proximal centriole lies perpendicular to the end of the distal centriole and is attached to it by fibro-granular material. Pro-acrosomal vesicles migrate anteriorly through the cytoplasm and move into the anterior filament to one side of the expanding nucleus. Eventually these vesicles migrate all the way to the tip of the sperm, where they fuse to form one of two granules in the acrosome. In mature sperm the nucleus is bullet-shaped with a long anterior filament and contains dense chromatin with occasional lacunae. The mitochondria vary in both number and position in the mature sperm of different species. Both centrioles are housed eccentrically in a posterior indentation of the nucleus, where the membranes are modified. The elongate flagellum tapers to a long filamentous end-piece that roughly corresponds to the anterior filament and may be important in sperm locomotion for hydrodynamic reasons. An acrosome is present in all ten species and stained positively for acid phosphatase in three species that were tested.     

The spermatogenesis and sperm structure of Timema poppensis (Insecta: Phasmatodea)

The ultrastructure of spermatogenesis and spermatozoa was studied in Timema poppensis Vickery & Sandoval, 1999, a putative basal taxon of Phasmatodea. The apical portion of testis follicles consists of spermatogonial cells with polymorphic nuclei. Primary spermatocytes display very short primary cilia originating from the peripheral centrosomes. Early spermatids develop a conspicuous “nebenkern” consisting of fused mitochondria. They have a single peripheral centriole with microtubular triplets, which expresses a 3.6-μm-long cilium featuring a 9?+?2 axonemal pattern. In a later stage, the centriole and the ciliary shaft displace toward the inner part of the cytoplasm by an infolding of the plasma membrane. Mature spermatids exhibit a derived centriole with microtubule doublets devoid of dynein arms, which is equipped with a dense arc-like outer structure. Ciliary degeneration was not observed during spermiogenesis. Spermatozoa are short flagellate cells about 55–60?μm in length. They are characterized by a three-layered acrosomal complex. The distinctive bell-shaped morphology of the acrosome vesicle is likely an autapomorphic trait of Timema. The flagellum has a 9?+?9?+?2 axoneme, two accessory bodies, two flattened cisterns, and two elongated mitochondrial derivatives. Results support the hypothesis that Phasmatodea, comprising Timema?+?Euphasmatodea, form a monophyletic group. The presence of 17 protofilaments in the wall of accessory microtubules and the flattened configuration of the flagellum are potential apomorphic groundplan features of the order. Within Phasmatodea, a key evolutionary divergence was from the conventional insect spermiogenesis and sperm structure of Timema, to the unusual spermiogenetic process and peculiar sperm structure of Euphasmatodea. As a result, Timema retains more sperm character states found in the polyneopteran ground pattern, while Euphasmatodea have evolved outstanding sperm autapomorphies, like the loss of mitochondria and flattened cisterns, and the presence of strongly expanded accessory bodies.     

Sperm and spermatozeugma ultrastructure in the inseminating species Tyttocharax cochui, T. tambopatensis, and Scopaeocharax rhinodus (Pisces: Teleostei: Characidae: Glandulocaudinae: Xenurobryconini)

This article presents the scanning and transmission electron microscopy of the spermatozoa and sperm packets of three inseminating species of the glandulocaudine tribe Xenurobryconini. All three species, Scopaeocharax rhinodus, Tyttocharax cochui, and T. tambopatensis produce unencapsulated sperm packets (= spermatozeugmata) of similar morphology. The external anterior surface of each spermatozeugma is comprised of elongate sperm heads arranged in parallel, and the posterior part is made up of tightly packed flagella. The interior of the anterior portion consists of alternating layers of sperm heads and flagella. The remarkable integrity of each packet appears to be maintained through an electron-dense secretion seen among all parts of the cells. Spermatozeugma formation takes place within the spermatocysts at the end of spermiogenesis and at spermiation fully formed packets are released. Morphology of the mature spermatozoa was similar in all three species. Each nucleus is elongate, flattened along most of its length, and tapers at either end. The two centrioles are nearly parallel to one another and are located just anterior to the nucleus. Elongate mitochondria are located along the nucleus. The single flagellum, which lacks axonemal fins, is initially contained within a short cytoplasmic collar. Accessory microtubules run parallel to the long axis of the nucleus just beneath the plasma membrane. During spermiogenesis, no nuclear rotation occurs and the cytoplasmic canal containing the flagellum elongates along with the nucleus. However, prior to spermiation all but the anterior portion of the collar degenerates. The sperm modifications observed in these species are discussed as adaptations to the unique reproductive habit of insemination.     

Spermiogenesis in the Pycnogonid Pycnogonum littorale (Ström)

Abstract Spermatids in different stages of development are connected by intercellular bridges. Later the disappearance of these is correlated with sloughing off the residual cytoplasm. At the onset of spermiogenesis, chromatin is agglomerated at the periphery of the nucleus. Later this disperses and no chromatin condensation takes place. There is a steady reduction in the nucleus size. This is correlated with increase in the number of small vesicles and microtubules in the cytoplasm. Eventually the nucleus becomes very small, and is surrounded by a complex system of microtubules. Following spermiogenesis process the mitochondria lose their cristae and contain adielectronic material. The mature sperm is spindle-shaped, tapering at both ends. In both ends there are only microtubules present terminating freely in the cytoplasm. In its middle there are a number of rod-shaped mitochondria containing an electron dense material. The microtubules in the middle part of the sperm are arranged in a hexagonal pattern and in others in rows interspersed with single ones. The structure of Pycnogonum littorale sperm is highly modified, which may explain the special mode of fertilisation.     

Ultrastructure of spermatogenesis and spermatozoa of Cephalodasys maximus (Gastrotricha,Macrodasyida)

Summary Spermatogenesis and sperm ultrastructure of the macrodasyidan gastrotrich Cephalodasys maximus are described by means of transmission electron microscopy. The filiform sperm consists of an acrosomal accessory structure and an acrosomal vesicle, both being surrounded by spiralled material. The successive nuclear helix encloses the spiral-shaped mitochondrion and the axoneme of the flagellum is accompanied by dense strings, three helical elements and peripheral microtubules. During spermiogenesis the acrosomal accessory structure develops first and moves into a cell projection, where the spiral around this acrosomal rod forms. A nuclear section with condensed chromatin and one single fused large mitochondrion follow into the extension, becoming helical. A connecting clasp between nucleus and flagellum shortens to a cap-like structure. Parallel to the acrosomal and nuclear projection the flagellum develops where the spiralled elements and the basal plate form in succession, while the basal body shrinks.     

ULTRASTRUCTURE OF SWARMERS IN THE LAMINARIALES (PHAEOPHYCEAE). II. SPERM1

The ultrastructure of sperm from 13 species in 11 genera of Laminariales collected in the northeast Pacific Ocean is unique in the brown algae. The sperm are elongate, and possess a nucleus, several mitochondria and two or three chloroplasts, but no eyespot. The anterior flagellum bears mastigonemes on the proximal half of its length; a distal “whiplash” portion lacks mastigonemes and is an extension of only the two central singlet microtubules of the axoneme. A peculiar feature of these sperm is the posterior flagellum, which is longer than the anterior flagellum and tapers distally as the doublet microtubules become singlets and decrease in number. This feature contrasts with the laminarialean zoospore, which possesses a short posterior flagellum with the usual “9 + 2” axoneme. The structure of these sperm differs from that reported for Chorda, the sperm of which resembles a primitive brown algal zoospore. The facts support the concept that Chorda is the most primitive member of the Laminariales.     

Ultrastructure of spermiogenesis and mature spermatozoon of Anonchotaenia globata (von Linstow, 1879) (Cestoda,Cyclophyllidea, Paruterinidae)

Yoneva, A., Georgieva, K., Mizinska, Y., Nikolov, P. N., Georgiev, B. B. and Stoitsova, S. R. 2010. Ultrastructure of spermiogenesis and mature spermatozoon of Anonchotaenia globata (von Linstow, 1879) (Cestoda, Cyclophyllidea, Paruterinidae). — Acta Zoologica (Stockholm) 91 : 184–192 The ultrastructure of spermiogenesis and of the spermatozoon of a species of the family Paruterinidae is described for the first time. The spermiogenesis of Anonchotaenia globata starts with the formation of a differentiation zone with two centrioles associated with thin striated roots. One of the centrioles gives rise to a free flagellum followed by a slight flagellar rotation and a proximodistal fusion of the flagellum with the cytoplasmic protrusion. This pattern corresponds to Type III spermiogenesis in cestodes. The spermatozoon consists of five distinct regions. The anterior extremity possesses an apical cone and a single helically coiled crested body. The cortical microtubules are spirally arranged. The axoneme is surrounded by a periaxonemal sheath and a thin layer of cytoplasm filled with electron‐dense granules in Regions I–V. The periaxonemal sheath is connected with the peripheral microtubules by transverse intracytoplasmic walls in Regions III and IV. The nucleus is spirally coiled around the axoneme. Anonchotaenia globata differs from Dilepididae (where paruterinids have previously been classified) in the type of spermiogenesis, the lack of glycogen inclusions and the presence of intracytoplasmic walls. The pattern of spermiogenesis is similar to that in Metadilepididae and Taeniidae, which are considered phylogenetically close to Paruterinidae.     

Fine structure of spermatozoa and spermatogenesis ofSchizomus palaciosi,Reddell and Cokendolpher, 1986 (Arachnida: Uropygi,Schizomida)

Summary Spermatogenesis ofSchizomus palaciosi occurs in cysts in paired tubular testes located ventrally in the opisthosoma. Only few germ cells comprise one cyst. In early spermiogenesis an acrosomal complex composed of a spherical vacuole and a short acrosomal filament is established opposite of which a 9×2+3 flagellum emerges from a flagellar tunnel. The latter, however, is only a short-lasting structure. A manchette of microtubules surrounds nucleus and part of the acrosomal vacuole. The alterations in the arrangement of the microtubules during spermiogenesis are described. The spermatid finally is an elongate cell with a slender acrosomal vacuole on top of the helical nucleus. A deep implantation fossa filled with dense material is encountered. The acrosomal vacuole is accompanied by an intricate paracrosomal lattice structure not known at present of otherArachnida. This structure disappears during final spermiogenesis. The acrosomal filament (perforatorium) reveals filamentous subunits arranged in a regular pattern. Large ovoid mitochondria do not establish a distinct middle piece. Finally the elongate spermatid is coiled to form the mature spherical spermatozoon.The results are discussed under functional and taxonomical aspects.     

UNUSUAL MICROTUBULAR PATTERNS AND THREE-DIMENSIONAL MOVEMENT OF MEALYBUG SPERM AND SPERM BUNDLES

The spermatozoon of the mealybug Pseudococcus obscurus Essig is a filamentous cell (0.25 µ by 300 µ) which exhibits three-dimensional flagellations throughout most of its length. It has microtubules (200 A diameter) and a threadlike nuclear core (0.07–0.09 µ diameter) which extend almost its entire length, but apparently it has no mitochondria, centrioles, typical flagellum, or acrosome. The microtubules are arranged in two and a half concentric rings and total 56 in the most actively motile region but form two or three concentric rings with totals of 28 or 56 tubules, respectively, in less active regions. The relation of unusual microtubular patterns to the 9 + 2 complex and to flagellar motion is discussed. Mealybug spermatozoa are transmitted to the female in motile bundles which are approximately 1.3 µ by 750 µ and have four regions: (1) an anterior corkscrew region; (2) a region which contains approximately 16 spermatozoa; (3) a region of amorphous content; and (4) an endpiece. Bundle motility originates from the synchronous movements of its spermatozoa which appear to be arranged in two concentric multistranded helices. The spermatozoa provide both forward and gyratory motions of the bundle, and the corkscrew complements bundle propulsion by converting part of the rotation into forward movement.     

Morphology of the male reproductive system and sperm ultrastructure of Leucoptera coffeella (Lepidoptera: Lyonetiidae)

The male reproductive tract of Leucoptera coffeella was processed for light and transmission electron microscopy. In the testis, the eupyrene cells are arranged in individual cysts, while the apyrene cysts form aggregates, never observed in other Lepidoptera. Both cysts contain 128 spermatozoa, which differ from the typical pattern. In the seminal vesicle, both types of spermatozoa are dispersed in the lumen, also different from other Lepidoptera. The apyrene spermatozoa are similar to those observed for other Lepidoptera. They present an anterior region covered by a dense cap and the flagellum is composed of a 9 + 9 + 2 axoneme and two mitochondrial derivatives. The eupyrene spermatozoa, however, differ from the typical pattern for Lepidoptera. Their anterior region contains a nucleus, an acrosome and a peculiar arc of eight accessory microtubules connected to the plasma membrane by dense bridges. In the nucleus–flagellum region, the ninth accessory microtubule is assembled between both mitochondrial derivatives, to participate in the axoneme. The flagellum comprises a 9 + 9 + 2 axoneme and two mitochondrial derivatives with paracrystalline cores. External to the plasma membrane and close to the accessory microtubules, there are tufts of an amorphous material, suggesting reduced lacinate appendages, while the reticular ones are absent. The reduction of lacinate appendages and the absence of sperm bundles in the seminal vesicle support the concept that the appendages of other Lepidoptera could be associated with the eupyrene aggregations. The characters ‘number of spermatozoa per cyst’ and ‘absence of bundles’ should be considered plesiomorphic, supporting the position of this taxon in the base of the Ditrysia.     

The ultrastructure of amberjack (Seriola dumerilii) sperm

Scanning and transmission electron microscopy were used to investigate the fine structure of sperm of the Mediterranean amberjack Seriola dumerilii. Each spermatozoon has an ovoid head which lacks an acrosome, a short, irregularly-shaped midpiece and a long flagellar tail. The midpiece houses eight spherical mitochondria, which are separated from the axoneme by the cytoplasmic canal. The centrioles are arranged approximately at right angles to each other. The proximal centriole lies inside, and the distal centriole outside, the nuclear fossa. The flagellum is inserted eccentrically into the head and is tangential to the nucleus, so that the spermatozoon is asymmetrical. It contains the conventional 9 + 2 axoneme, shows intratubular differentiations in the A microtubules of doublets 1, 2, 5 and 6, and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the amberjack sperm resembles type II sperm as defined previously, except for the presence of the proximal centriole inside the nuclear fossa. This could result from a partial rotation of the nucleus during spermiogenesis.     

Ultrastructure of the sperm and spermatogenesis and spermiogenesis of Dina lineata (hirudinea,erpobdellidae)

The mature sperm of Dina lineata is of the modified type. The sperm are 48 μm long and 0.3 μm wide. The sperm are filiform and helicoidal cells with a distinct head, a midpiece, and a tail. There are two distinct regions in the head: the acrosome and the posterior acrosome, each with its own characteristic morphology. The midpiece is the mitochondrial region and has a single mitochondrion. Two distinct portions can be observed in the tail: the axonematic region and the terminal piece. In the process of spermatogenesis the early spermatogonia divide to form a poliplast of 512 spermatic cells. In the spermiogenesis the following sequential stages can be distinguished: elongation of the flagellum; reciprocal migration of mitochondria and Golgi complex; condensation of chromatin and formation of the posterior acrosome; spiralization of nuclear and mitochondrial regions; and, finally, formation of the anterior acrosome. The extreme morphological complexity of the Dina spermatozoon is related to the peculiar hypodermal fertilization which characterizes the erpobdellid family. Correlation between sperm morphology and fertilization biology in the Annelida is revised.     

The sperm of Hexagenia (Pseudeatonica) albivitta Walker (Ephemeroptera: Fossoriae: Ephemeridae)

This study describes the sperm morphology of the mayfly Hexagenia (Pseudeatonica) albivitta (Ephemeroptera). Its spermatozoon measures approximately 30 μm of which 9 μm corresponds to the head. The head is composed of an approximately round acrosomal vesicle and a cylindrical nucleus. The nucleus has two concavities, one in the anterior tip, where the acrosomal vesicle is inserted and a deeper one at its base, where the flagellum components are inserted. The flagellum is composed of an axoneme, a mitochondrion and a dense rod adjacent to the mitochondrion. A centriolar adjunct is also observed surrounding the axoneme in the initial portion of the flagellum and extends along the flagellum for at least 2 μm, surrounding the axoneme in a half‐moon shape. The axoneme is the longest component of the flagellum, and it follows the 9+9+0 pattern, with no central pair of microtubules. At the posterior region of the flagellum, the mitochondrion has a dumb‐bell shape in cross sections that, together with the rectangular mitochondrial‐associated rod, is responsible for the flattened shape of the flagellum. An internal membrane is observed surrounding both mitochondrion and its associated structure.     

Spermatozoon ultrastructure of Aponurus laguncula (Digenea: Lecithasteridae), a parasite of Aluterus monoceros (Pisces: Teleostei)

The mature spermatozoon of Aponurus laguncula, a parasite of the unicorn leatherjacket Aluterus monoceros, was studied by transmission electron microscopy. The spermatozoon possesses 2 axonemes of the 9 + “1” trepaxonematan pattern, attachment zones, a nucleus, a mitochondrion, external ornamentation of the plasma membrane and cortical microtubules. The major features are the presence of: 1) external ornamentation in the anterior part of the spermatozoon not associated with cortical microtubules; 2) one mitochondrion; and 3) cortical microtubules arranged as a single field in the ventral side. The maximum number of microtubules is in the nuclear region. The extremities of the axonemes are characterized by the disappearance of the central core and the presence of microtubule doublets or singlets. This study is the first undertaken with a member of the Lecithasteridae and exemplifies the sperm ultrastructure for the superfamily Hemiuroidea.     

Sperm of Doradidae (Teleostei: Siluriformes)

Spermatic characteristics were studied in 10 species representing several distinct groups within the catfish family Doradidae. Interestingly, different types of spermatogenesis, spermiogenesis and spermatozoa are correlated with intrafamilial groups previously proposed for Doradidae. Semi-cystic spermatogenesis, modified Type III spermiogenesis, and biflagellate sperm appear to be unique within Doradidae to the subfamily Astrodoradinae. Other doradid species have sperm with a single flagellum, cystic spermatogenesis, and spermiogenesis of Type I (Pterodoras granulosus, Rhinodoras dorbignyi), Type I modified (Oxydoras kneri), or Type III (Trachydoras paraguayensis). Doradids have an external mode of fertilization, and share a few spermatic characteristics, such as cystic spermatogenesis, Type I spermiogenesis and uniflagellate sperm, with its sister group Auchenipteridae, a family exhibiting sperm modifications associated with insemination and internal fertilization. Semi-cystic spermatogenesis and biflagellate spermatozoa are also found in Aspredinidae, and corroborate recent proposals that Aspredinidae and Doradoidea (Doradidae + Auchenipteridae) are sister groups and that Astrodoradinae occupies a basal position within Doradidae. The co-occurrence in various catfish families of semi-cystic spermatogenesis and either biflagellate spermatozoa (Aspredinidae, Cetopsidae, Doradidae, Malapturidae, Nematogenyidae) or uniflagellate sperm with two axonemes (Ariidae) reinforces the suggestion that such characteristics are correlated. Semi-cystic spermatogenesis and biflagellate sperm may represent ancestral conditions for Loricarioidei and Siluroidei of Siluriformes as they occur in putatively basal members of each suborder, Nematogenyidae and Cetopsidae, respectively. However, if semi-cystic spermatogenesis and biflagellate sperm are ancestral for Siluriformes, cystic spermatogenesis and uniflagellate sperm have arisen independently in multiple lineages including Diplomystidae, sister group to Siluroidei.     

Fine structure of the spermatozoa of Crassostrea gigas (Mollusca,Bivalvia)

We describe sperm ultrastructure and acrosome differentiation during spermiogenesis in Crassostrea gigas (Mollusca Bivalvia). The sperm cell is a uniflagellated cell of the primitive type. The head region contains a rounded or conical nucleus surmounted by small acrosome. This organelle consists of a membrane-bound acrosomal granule, the contents of which have a homogeneous density, except in the anterior region, which is positive for PTA. The acrosome also surrounds the perforatorium, which includes oriented fibrillar elements: this is the axial body. The middle piece contains four mitochondria encircling two perpendicular centrioles. The distal centriole is provided with a system of mechanical fixation to the plasma membrane, consisting of nine fibers in radial arrangement. The tail flagellum, about 50 m?m long, contains the usual microtubular axoneme. © 1993 Wiley-Liss, Inc.     

Structure of the Testes,Spermatozoa and Spermatozeugmata of Mimagoniates barberiRegan, 1907 (Teleostei: Characidae), an Internally Fertilizing,Oviparous Fish

Abstract The testis of Mimagoniates barberiis bipartite. Spermatogenic tissue is restricted to the anterior part. The posterior part of the testis is devoid of spermatogenic tissue and contains numerous efferent ducts filled with mature sperm. Cells in germinal cysts develop synchronously, sperm nuclei and flagella become oriented parallel in the late stages of spermiogenesis. In the caudal portion of the aspermatogenic part all sperms are arranged into unencapsulated sperm bundles — spermatozeugmata. Two types of spermatozeugmata are found both in the caudal portion of the testis and in milt. In the larger, spindle–shaped type, sperm flagella form the spindle tips. In the smaller ones, which have approximately a length of spermatozoon, the sperm are parallel and approximately in register. In both types sperm heads are arranged parallel. A mature spermatozoon is flail–shaped. The sperm head is highly elongated and situated alongside the flagellum, the tip of the head is directed backwards. Large mitochondria are situated on one side of the elongated nucleus only and form the tip of the head. Live spermatozoa move with the centriolar part ahead. Both testis and spermatozoon structure as well as formation of spermatozeugmata in M. barberiare highly derived features which perhaps evolved as adaptations to internal fertilization.