Ultrastructure of the spermatozoon ofElenchus japonicus and its bearing on the phylogeny of strepsiptera

The fine structure of the mature spermatozoon of the strepsipteranElenchus japonicus Esaki and Hashimoto (Elenchidae) is described using transmission electron microscopy. The spermatozoon was seen to have an elongated head, a tail containing a 9 + 9 + 2 axoneme, two mitochondrial derivatives and two accessory sheaths. The monolayered acrosome is conical in shape while the nucleus exhibits an internal channel of uncondensed chromatin. The tail is long, and in its final portion, the axoneme, loses its elements progressively. These results are compared with the sperm ultrastructure ofXenos moutoni De Buysson (Stylopidae) and with those of other insect orders, particularly the Coleoptera.     

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.     

The ultrastructure of spermiogenesis and spermatozoa in Diplomystes mesembrinus

Spermiogenesis in Diplomystes mesembrinus , one of the most primitive species from the Siluriformes, occurs in cysts. Differentiation of spermatids is characterized by chromatin compaction, flagellum development, nuclear fossa formation, rotation of the nucleus, and excess cytoplasm elimination. The spermatozoon head is round, the nucleus contains highly condensed chromatin clusters, the midpiece is short, the axoneme shows a 9 +2 pattern with two discrete lateral projections, and the acrosome is absent. The nuclear fossa penetrates deeply into the nucleus, including the centriolar complex and the start of the axoneme. The single large C-shaped mitochondrion surrounds the initial segment of the axoneme. The structural features of D. mesembrinus spermatozoon are similar to the Clupeiformes.     

Ultrastructure of the spermatozoon of the mosquito Toxorhynchites (Diptera, Culicidae)

The spermatozoon of Toxorhynchites brevipalpis conradti Gruenberg is long and filiform. It contains an anterior nucleus, an axoneme of the 9 + 9 +"1" pattern and two mitochondrial derivatives. Comparison of our observations with bibliographical data shows that spermatozoon ultrastructure is homogeneous in the family Culicidae (Culicinae, Anophelinae and Toxorhyn-chitinae). The 9 + 9 +"1" pattern of the sperm axoneme may be considered a synapomorphy of the Culicidae.     

The spermatozoon of a 'living fossil': Tubiluchus troglodytes (Priapulida)

The spermatozoon of Tubiluchus troglodytes, the first priapulid formally described from the Mediterranean Sea has a head composed of an acrosome and a nucleus. The acrosome is divided in two branches coiled around the nucleus. The nucleus is basally columnar, but apically generates two rods helically coiled one around the other. The midpiece is formed by an axoneme with 27 accessory microtubules, surrounded by three mitochondria. An annulus separates the midpiece from the tail that contains a 9 + 2 axoneme surrounded by nine accessory microtubules. The spermatozoon of T. troglodytes is similar to that of the other two species known from the genus, and completely different from the 'primitive' one of the other priapulids. Since Tubiluchus is considered the most basal of the extant priapulids, and the only genus with an internal fertilization, it may be that in priapulids the external fertilization is a derived character.     

Morphology of testicular and post-testicular spermatozoa in Microstigmus arlei Richards, 1972 and M. nigrophthalmus Melo, 1992 (Hymenoptera: Apoidea: Pemphredoninae) with phylogenetic consideration

The sperm of Microstigmus arlei and Microstigmus nigrophthalmus are twisted in a spiral and consist of two regions: the head, formed by an acrosome and a nucleus, and the flagellum, formed by two asymmetric mitochondrial derivatives, a long centriolar adjunct, an axoneme (9+9+2) and two accessory bodies. The head shows a characteristic morphology. The acrosome is very long and is basically made up of a paracrystalline structure. In the central head region, the acrosome is inserted into the nucleus, which is observed coiling laterally around the paracrystalline structure. In the subsequent part of the spermatozoon the nucleus appears round in transverse sections, and over some length it is still penetrated by the acrosome until shortly distal to the flagellar insertion. At this point the nucleus forms an inverted cone-shaped projection. These morphological characteristics of acrosome and nucleus of the Microstigmus wasp have not been previously described in Apoidea and are useful for phylogenetic evaluation of this superfamily.     

Ultrastructure of apyrene and eupyrene spermatozoa from the seminal vesicle of Euptoieta hegesia (Lepidoptera: Nymphalidae)

The ultrastructure of the seminal vesicle's spermatozoa of the butterfly Euptoieta hegesia was analyzed. The apyrene spermatozoa measure about 300 microm in length and swim freely in a secretion. The anterior end consists in a cap with a cylindrical extension and a globular structure. The flagellum has a 9+9+2 axoneme, two mitochondrial derivatives with paracrystalline matrices and an external coat formed by concentric layers. The eupyrene spermatozoa measure about 550 microm in length and are grouped into bundles. The anterior end consists in an amorphous globule. Posterior to this globule, a coat with a dense material covers the spermatozoon where an acrosome and a nucleus appear. The flagellum has a 9+9+2 axoneme and two mitochondrial derivatives. External to the coat and attached to the dense material, there is a reticular appendage, which has a paracrystalline core and extends to the distal tip of the spermatozoon.     

Sperm structure of Mecoptera and Siphonaptera (Insecta) and the phylogenetic position of<Emphasis Type="Italic"> Boreus hyemalis</Emphasis>

Sperm ultrastructure has been studied in three species of the taxa Mecoptera and Siphonaptera. The spermatozoon of the scorpion fly Panorpa germanica shows an apical bilayered acrosome, a helicoidal nucleus, a centriolar region and a 9+2 flagellar axoneme helicoidally arranged around a long mitochondrial derivative. A second mitochondrial derivative is very short and present only in the centriolar region. A single accessory body is present and it is clearly formed as a prolongation of the centriole adjunct material. Two lateral lamellae run parallel to the nucleus. The snow fly Boreus hyemalis has a conventional sperm structure and shows a bilayered acrosome, a long nucleus, a centriolar region, two mitochondrial derivatives and two accessory bodies. The axoneme is of the 9+2 type and is flattened at the tail tip. Both P. germanica and B. hyemalis have two longitudinal extra-axonemal rods and have a glycocalyx consisting of longitudinal parallel ridges or filaments. The spermatozoon of the flea Ctenocephalides canis has a long apical bilayered acrosome, a nucleus, a centriolar region, a 9+2 axoneme wound around two unequally sized mitochondrial derivatives, and two triangular accessory bodies. In the posterior tail end the flagellar axoneme disorganises and a few microtubular doublets run helicoidally around the remnant mitochondrial derivative. The glycocalyx consists of fine transverse striations. In all three species, the posterior tail tip is characterised by a dense matrix embedding the disorganised axoneme. From this comparative analysis of the sperm structure it is concluded that Mecoptera, as traditionally defined, is monophyletic and that B. hyemalis is a member of Mecoptera rather than of Siphonaptera.     

Fine structure of the spermatozoon of the strepsipteran Xenos moutoni

Spermatozoa of Xenos moutoni De Buysson belonging to the order Strepsiptera (Insecta) were examined by electron microscopy. The spermatozoon was seen to have an elongated head and a tail containing a 9+9+2 axoneme and two mitochondrial derivatives of equal size. The pear-shaped acrosome is characterised by a mono-layered structure and terminates anteriorly forming two pyramidal evaginations. The nucleus exhibits an external portion of dense chromatin and an internal one of uncondensed material. The latter occupies a central position at the base and becomes progressively peripheral at the apex. The tail is long and in its final portion the axoneme loses its elements progressively. These results have been compared with the ultrastructure of the spermatozoa of Coleoptera which have been considered as a sister group of Strepsiptera.     

黄姑鱼（ Nibea albiflora） 与大黄鱼（ Pseudosciaena crocea） 精子超微结构的观察与比较

应用扫描电镜（SEM）与透射电镜（TEM）观察了黄姑鱼和大黄鱼精子的超微结构。结果显示,黄姑鱼和大黄鱼精子无论在形态、大小还是超微结构上都十分相似。黄姑鱼和大黄鱼精子均由头部、中段和尾部（鞭毛）3部分组成。精子头部形状近似椭圆形,无顶体,细胞核呈肾形。中心粒复合体位于细胞核背侧,近、远端中心粒相互垂直,远端中心粒分化成基体并形成轴丝。中段的袖套呈筒状,4～5个圆形的线粒体围绕轴丝呈环形排列。精子尾部为单鞭毛,轴丝为典型“9＋2”结构,鞭毛表面质膜形成不规则侧鳍。     

大黄鱼精子的超微结构

大黄鱼的精子由头产和尾部两部分组成。头部结构较为独特,其腹侧有一较大的细胞核,背部有中心粒复合体。头部的后端是袖套。细胞核的腹面稍向外突出背面则稍向内凹。细胞核中的染以质浓缩成致密的团块状。团块状的染色质之间分布着松散的纤维状染色质。植入窝位于细胞核的背部表面,由细胞核背面向内凹陷而成,呈一沟状,其走向与精子的长轴平行。     

Ultrastructure of the spermatozoon of Megaselia scalaris Loew (Diptera:Brachycera:Cyclorrhapha:Phoridea:Phoridae)

When viewed by scanning electron microscopy (SEM), the spermatozoon of the phorid dipteran Megaselia scalaris appears threadlike, lacking distinct head and tail areas. These areas can be observed, however, in appropriately stained material. Measurements of Feulgen-stained material reveal average lengths of the head, tail, and total cell of 18.7, 128.7, and 147.4 μm, respectively. When tested for sulfhydryl and disulfide groups, the head displays only disulfide groups. Transmission electron microscopy (TEM) reveals 12 different regions: three (1–3) in the head, four (9–12) in the tail, and five (4–8) in a short zone of overlap between the head and tail. Most of the cell lies in regions 9 and 11 of the tail and 3 of the head, accounting for, respectively, 37.3%, 45.7%, and 11.2% of the total length. A tubelike acrosome indents the anterior end of the nucleus. The tail originates asymmetrically in relation to the long axis of the cell as a peglike structure associated with the dorsolateral region of the nucleus. No centriole is visible, and the nucleus has a notched appearance in longitudinal sections. Two mitochondrial derivatives and an axoneme displaying a 9+9+2 microtubule configuration and ATPase activity extend throughout most of the tail. In regions 9 and 10, an asymmetrically arranged accessory body is also present. Features having possible taxonomic utility include the asymmetrically arranged accessory body, the size and shape of the acrosome, and the notched appearance of the nucleus. The present report is apparently the first to describe the spermatozoon of a cyclorrhaphous dipteran which is not a member of the Schizophora.     

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.     

Fine structure of spermatozoa in the blackspot sea bream Pagellus bogaraveo (Brünnich, 1768) with some considerations about the centriolar complex

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the sparid fish Pagellus bogaraveo.The spermatozoon of P. bogaraveo belongs, like that of the other sparid fish, to the teleostean “type I” spermatozoon with the flagellar axis insert perpendicular to the nuclear fossa. It has an ovoidal head, a short, cylindrically shaped midpiece and a long tail region. The nucleus reveals a deep invagination (nuclear fossa), in which the centriolar complex is located, and a satellite nuclear notch shaped like a golf club. The two centrioles are perpendicular to each other and show a conventional “9+0” pattern. The distal centriole is attached to the nuclear envelope by means of basal feet and radial fibers made of electron-dense material. Below the basal plate, plasma membrane pinches in, and the necklace, a specialized connection joining axonemal doublets to the plasma membrane, is visible. The short midpiece houses one mitochondrion. The flagellum is perpendicularly and eccentrically with respect to the nucleus and contains the conventional “9+2” axoneme.     

Cryopreservation of Atlantic croaker spermatozoa: evaluation of morphological changes.

The spermatozoon of the Atlantic croaker (Micropogonias undulatus) is a primitive type in that it lacks an acrosome. The kidney-shaped head has a diameter of about 1.5 microns and is occupied by a granular and electron-dense nucleus. The short midpiece contains 3 spherical mitochondria and encircles the basal body of the flagellum but is separated from it. The flagellum consists of the typical 9 + 2 axoneme and surrounding plasma membrane but lacks a lateral ridge. Spermatozoa of Atlantic croaker diluted in either NaCl or sodium citrate solutions with or without DMSO were examined with the electron microscope before freezing in liquid nitrogen and after thawing. Damage following cryopreservation appeared to be greater to the mitochondria, plasma membrane, and 9 + 2 axoneme than to the nucleus. The incidence of postthaw damage in spermatozoa diluted with NaCl solutions containing DMSO was remarkably lower than that with either pure NaCl solutions, pure sodium citrate solutions, or sodium citrate solutions containing DMSO.     

Ultrastructural study of spermiogenesis and the spermatozoon in Catenotaenia pusilla, an intestinal parasite of Mus musculus

The ultrastructure of spermiogenesis and the mature spermatozoon in Catenotaenia pusilla (Cestoda: Catenotaeniidae) is described. Spermiogenesis is characterized by the presence of a single axoneme which grows on the outside of a cytoplasmic extension at an angle of 45 degrees. Flagellar rotation and proximodistal fusion are produced in this process. The centrioles lack striated roots and an intercentriolar body. In the mature spermatozoon four different regions are described. The anterior extremity is capped by an apical cone and presents two helical crest-like bodies of unequal length. The axoneme, of the 9 + '1' pattern of the Trepaxonemata, presents a periaxonemal sheath. The cortical microtubules form a spiral pattern at an angle of about 40 degrees to the hypothetical spermatozoon axis. The nucleus is kidney- to horseshoe-shaped in cross section. Granules and proteinaceus walls are not observed in the spermatozoon of C. pusilla.     

Ultrastructural study of spermatogenesis and the spermatozoon in Postorchigenes gymnesicus (Trematoda,Lecithodendriidae)

An ultrastructural study of spermatogenesis, spermiogenesis, and spermatozoa in Postorchigenes gymnesicus is presented. Cytoplasmic projections originating in nurse cells surround the spermatogonia, which are located at the periphery of the testes. Primary spermatocytes attached to a cytophore show synaptonemal complexes and a pair of centrioles. Spermiogenesis begins with the appearance of a cytoskeletal structure formed by an intercentriolar body and two perpendicular centrioles. An axoneme and a striated rootlet emerge from each centriole. The progressive rotation and fusion of both flagella with the median process occurs simultaneously with the migration of nucleus to the distal tip of the forming spermatozoon. The mature spermatozoon consists of three regions: (1) the nuclear region, containing the nucleus, one mitochondrion, two 9+1 axonemes, and cortical microtubules; (2) the intermitochondrial region, containing two axonemes; and (3) the mitochondrial region with another mitochondrion, two axonemes, cortical microtubules, and external ornamentation symmetrically and asymmetrically arranged coincidental with the cortical microtubules. Glycogen particles, absent in testicular cells, are abundant in the spermatozoon. Ultrastructural features of the non-nuclear region of the spermatozoon are specific for P. gymnesicus and are proposed to characterize the spermatozoon of digenean species. J. Morphol. 234:223–232, 1997. © 1997 Wiley-Liss, Inc.     

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.     

Reinvestigation of the ultrastructure of spermiogenesis and the spermatozoon of Hymenolepis nana (Cestoda, Cyclophyllidea), parasite of the small intestine of Rattus rattus.

Spermiogenesis in Hymenolepsis nana begins with the formation of a differentiation zone. This is limited at the front by arched membranes, is surrounded by cortical microtubules associated with 12 crested-like bodies, and contains a single centriole made up of doublets. The distal centriole gives rise to a flagellum that grows at the same pace as the cortical microtubules. Migration of the nucleus takes place after the formation of the flagellum. It is followed by the separation of the old spermatid from the residual cytoplasm. The mature H. nana spermatozoon is filiform and lacks mitochondria. The axoneme, of the 9 + "1" pattern of the Platyhelminthes, does not reach the extremities of the spermatozoon. The nucleus is electron dense and is in close contact with the axoneme around which it coils in a spiral making an angle of 10 degrees to 15 degrees with the spermatozoon axis. The cortical microtubules follow a 10 degrees to 15 degrees helicoidal path along almost their whole length, except at their posterior extremity, where they are parallel to the spermatozoon axis. H. nana is distinguished by the early development of 12 crested-like bodies of different lengths and by the existence of a single centriole in the differentiation zone. Such a high number of crested-like bodies had never previously been reported in a cestode.