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.     

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。     

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.     

Unusual features of sperm ultrastructure in the musk shrew Suncus murinus

The spermatozoon of the Musk shrew Suncus murinus displays unusual fine anatomical features. In the head, the equatorial segment of the acrosome is recessed within a waist in the sperm nucleus in a way that could afford some protection for this fusogenic region, perhaps during penetration of the egg vestments. The perinuclear material has distinctive inner and outer regions, the latter being arranged as a series of coxcomblike spikes. These structures in Suncus could serve to anchor its characteristically giant acrosome to the sperm nucleus. In the tail, small aggregations of electron dense material appear against some centriolar triplets and also, proximally, against some axonemal doublets. In the midpiece, prominent satellite material aggregates proximally over the inner border of the dense fibers. More distally, the material maintains a close relationship with and primarily lies between the corresponding axonemal doublets and dense fibers 5 and 6, the latter being positioned asymmetrically in relation to the remaining dense fibers.     

中国绿螂精子的超微结构

应用透射电镜技术观察了中国绿螂(Glaucomya chinensis)精子的超微结构。精子为典型的原生型,包括头部、中段和尾部三部分。头部由顶体和细胞核组成。顶体呈倒"V"字型。细胞核呈长圆柱形,没有核前窝,具有核后窝。中段由4个线粒体环绕中心粒而成。尾部细长,为典型的"9+2"结构。文中还讨论了双壳类精子形态结构的种属间差异。     

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.     

Structure and ultrastructure of the spermatozoa of Bephratelloides pomorum (Fabricius) (Hymenoptera: Eurytomidae)

The spermatozoa of Bephratelloides pomorum are very long and fine. Each spermatozoon measures about 620 μm in length by 0.38 μm in diameter and, when seen under the light microscope, appears to be wavy along its entire length. The head, which is approximately 105 μm, comprises a small acrosome and a nucleus. The acrosome is made up of a cone-shaped acrosomal vesicle surrounding the perforatorium and the anterior end of the nucleus. Innumerable filaments radiate from it. The perforatorium has a diameter equal to that of the nucleus at their junction, where it fits with a concave base onto the rounded nuclear tip. The nucleus is helicoidal and completely filled with homogeneous compact chromatin. It is attached to the tail by a very long and quite electron-dense centriolar adjunct that extends anteriorly from the centriole in a spiral around the nucleus for approximately 8.5 μm. The tail consists of an axoneme with the 9+9+2 microtubule arrangement pitched in a long helix, as well as a pair of spiraling mitochondrial derivatives (with regularly arranged cristae) that coil around the axoneme, and two small accessory bodies. As well as the spiraling of the nucleus, mitochondrial derivatives and axonemal microtubules, the sperm of B. pomorum present other very different morphological features. These features include the acrosome and centriolar adjunct, both of which differentiate the spermatozoa from the majority of sperm found in other Hymenoptera. In addition these structural variations demonstrate that the sperm of chalcidoids provide characteristics that can certainly prove useful for future phylogenetic analysis at the subfamily level and, possibly, the genus too.     

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.     

白肛海地瓜精子发生及形态的超微结构

通过透射和扫描电镜观察了白肛海地瓜(Acaudina leucoprocta)的精子发生过程及其形态结构,揭示了白肛海地瓜精子发生时期一系列变化,其精子发生分为精原细胞、初级精母细胞、次级精母细胞、精细胞、成熟精子5个时期。精原细胞体积最大。精母细胞染色质开始凝集。精细胞前顶体颗粒形成。白肛海地瓜成熟精子的超微结构为原生型,由头部、中部、尾部组成,头部圆形,最前端为顶体,核染色质凝集成团块状,中部是线粒体和中心粒复合体融合成1个超大结构,尾部长约60μm,尾部鞭毛横切面为典型的"9+2"型结构。     

Sperm morphology of the Eurasian beaver, Castor fiber: an example of a species of rodent with highly derived and pleiomorphic sperm populations

The structural organization of the spermatozoon from the Eurasian beaver, Castor fiber (Family: Castoridae), was determined and compared to that of other sciuromorph rodents. The beaver spermatozoon has a head, which is variable in form but usually paddle-shaped, with a small nucleus and very large acrosome, and a tail that is relatively short compared to that of most other rodents. Transmission electron microscopy indicates that in most testicular spermatozoa the acrosome projects apically, although in a few it becomes partly flexed. During the final stages of maturation, however, the acrosome becomes highly folded so that the apical segment comes to lie alongside part of the acrosome that occurs lateral to the nucleus, with, in some cases, fusion taking place between the outer acrosomal membranes. The sperm nucleus is wedge-shaped, being broader basally and narrowing apically with an occasional large nuclear vacuole occurring. This spermatozoon structure is markedly different from that found in the other species of Geomyoidea, which is the sister group of the Castoridae. The findings thus emphasize the highly divergent nature of the beaver spermatozoon and demonstrate that, within the proposed Infraorder Castorimorpha, very large differences in sperm structure have evolved.     

Ultrastructure of spermatids and spermatozoa in three polychaetes with modified biology of reproduction: Autolytus sp., Chitinopoma serrula,and Capitella capitata

Unlike the primitive type of spermatozoon found in most polychaetes, the spermatozoon of Autolytus has a bilateral symmetry with elongated nucleus, and the mitochondria surround the posterior part of the nucleus. A rather large disk-shaped acrosome is situated along one side of the anterior part of the nucleus. From the anterior margin of the distal centriole emerge long striated rootlets, which run along the nuclear envelope to the anterior part of the nucleus. The spermatozoon of Chitinopoma serrula has an elongated, slightly bent nucleus, a thimble-like acrosome apically on the anterior surface of the nucleus, and an elongated middle piece containing 4 rod-like mitochondria developed from spherical mitochondria surrounding the basal part of the tail flagellum. In the spermatozoon of Capitella capitata, both nucleus and middle piece are elongated compared to the primitive type. The large and conical acrosome is placed asymmetrically at the nucleus and consists of an acrosomal vesicle and subacrosomal substance. The greater part of the middle piece forms a collar around the initial part of the tail flagellum. The cytoplasm of the collar contains granular material. One or two small mitochondria lie around the 2 centrioles at the base of the nucleus.

These types of spermatozoa represent early steps in the evolution of modified spermatozoa combined with changed biology of reproduction. The modified spermatozoa are larger than the primitive ones.     

大鲵精子的超微结构研究

本文运用透射电镜和扫描电镜研究了大鲵(Andrias davidianus)精子的超微结构,大鲵精子由头部(head),中片(midpiece)和尾部(tail)三部分组成。头部有棒状细胞核,核内染色质高度浓缩,细胞核前方呈细丝状,但非顶体结构。头部后端凹陷,称为植入窝(implantation fossa),植入窝内有线粒体和中心粒等细胞器结构,此区域为精子的中片。精子尾部细长,主要由轴丝和附属纤维(accessory fiber)组成,轴丝的外面具有波动膜。     

Elektronenmikroskopische Untersuchungen am Spermatozoon des Opossum (Didelphys virginiana Kerr)

Summary Spermatozoa from the epididymis of Didelphys virginiana Kerr have been investigated by means of light and electron microscopy.In the head of the spermatozoon the nucleus consists of a thick mass which has a deep cleft on the one side and an indentation on the other.The acrosome is long and flat. It is situated in the head of the spermatozoon near one side of the cleft.The tail of the spermatozoon is affixed to the nucleus by means of a budlike thickening which is inserted into the indentation. The fine structure of the tail is described in detail.Based on the electron micrographs a diagram has been devised to show the structural details described in the text.     

Comparative sperm ultrastructure of<Emphasis Type="Italic"> Neodasys ciritus</Emphasis> and<Emphasis Type="Italic"> Musellifer delamarei</Emphasis>, two species considered to be basal among Chaetonotida (Gastrotricha)

The spermatozoa of two species supposed to be basal to Gastrotricha Chaetonotida, Neodasys ciritus and Musellifer delamarei, were studied in order to supply further elements to the understanding of sperm evolution in Chaetonotida, a group in which a fully parthenogenetic reproduction is dominant. Two considerably different sperm patterns were found: the spermatozoon of N. ciritus has a simple, conical acrosome, a short, condensed nucleus, few conventional mitochondria randomly arranged along the sperm head, and a 9×2+2 flagellum perpendicular to the sperm major axis. The spermatozoon of M. delamarei is a filiform cell with a simple acrosome, a partially condensed nucleus, four mitochondria at the nuclear base, and a flagellum with a 9×2+2 axoneme and large accessory fibers. Some sperm features of M. delamarei are comparable to those of Xenotrichulidae, the only other Chaetonotida producing conventional spermatozoa, whereas the sperm of N. ciritus appears different from all the other patterns known among Gastrotricha, thus knowledge of it does not help in solving the problem of the discussed phylogenetic position of the genus.     

Ultrastructural study of spermiogenesis and the testicular and spermathecal spermatozoon of the Gonochoristic Tardigrade Xerobiotus pseudohufelandi (Eutardigrada,Macrobiotidae)

This paper investigates by scanning and transmission electron microscopy spermiogenesis and spermatozoon morphology of the gonochoristic eutardigrade Xerobiotus pseudohufelandi (Macrobiotidae). During spermiogenesis clusters of spermatids are connected by cytoplasmic bridges that persist up to an advanced stage of maturation. Spermiogenesis is characterized by distinctive modifications of the nucleus and by the differentiation of an acrosome, tail and substantial midpiece. Testicular spermatozoa are folded with the hinge located between the head and midpiece, thus resembling a nut-cracker. The head includes a rod-shaped, bilayered acrosome and an elongated, helicoidal nucleus with condensed chromatin. The large kidney-shaped midpiece has hemispherical swellings/ovoid elements surrounding the centriole and an incomplete mitochondrial sleeve. The flagellum contains a ‘9+2’ axoneme and terminates in a tuft of microtubules. Spermathecal spermatozoa always have linear profiles. The acrosome and nucleus have the same morphological pattern as in testicular spermatozoa, whereas the midpiece is thin and lacks the hemispherical swellings, and the tail is reduced to a short stub. Functional considerations are presented, based upon this different morphology. Moreover, phyletic comparisons are made on the basis of sperm morphology, both for the family Macrobiotidae and the class Eutardigrada. J. Morphol. 234:11–24, 1997. © 1997 Wiley-Liss, Inc.     

Fine structure of spermatozoa in the common pandora (Pagellus erythrinus Linnaeus, 1758) (Perciformes, Sparidae)

Scanning and transmission electron microscopy were used to investigate the fine structure of the sperm of the Sparid fish Pagellus erythrinus L. The spermatozoon of pandora has a spherical head lacking an acrosome, a cone-shaped midpiece and a long tail. The midpiece houses a single mitochondrion. The centriolar complex lies inside the nuclear fossa and is composed of a proximal and a distal centriole which are arranged at right angles to each other. The flagellum is inserted medio-laterally into the head, contains the conventional 9+2 axoneme and possesses one pair of lateral fins. On the basis of its ultrastructural organization, the pandora sperm can be regarded as an evolved form of the primitive spermatozoon found in Teleosts. According to the morphological classification proposed by Mattei (1970), the sperm of pandora belongs to a "type I" designation, like that of the other Sparid fish.     

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.     

Comparative spermatology of four species of strepsiptera and comparison with a species of primitive coleoptera (Rhipiphoridae)

The comparative spermatology of 4 strepsipteran species, namely, Xenos moutoni De Buysson, Elenchus tenuicornis (Kirby), Elenchus japonicus Esaki and Hashimoto and Halictophagus chilensis Hofmann, have been studied by transmission electron microscopy. The spermatozoon of all 4 species examined were seen to have: an elongated head characterized by a nucleus with an internal channel of uncondensed chromatin, a one-layered acrosome, and a tail containing a 9 + 9 + 2 axoneme and 2 partially crystallized mitochondrial derivatives. Each sperm, nevertheless, shows a few peculiarities that confirm the taxonomic value of comparative spermatology. In addition, the strepsipteran spermatozoa were seen to have a different organization to that of Pelecotoma fennica Pewkull (Rhipiphoridae, Pelecotominae), which has the typical structure of a coleopteran sperm. It was characterized by a 3-layered acrosomal complex, a tail with a 9 + 9 + 2 axoneme flanked by 2 accessory bodies and 2 mitochondrial derivatives. From the spermatological point of view, primitive Coleoptera cannot be considered to be closely related to Strepsiptera.     

中国雨蛙精子结构及其在系统发育上的意义

研究了中国雨蛙（Ｈｙｌａｃｈｉｎｅｎｓｉｓ）精子的超微结构,并初步探讨其在系统发育上的意义,中国雨蛙精子由头部和尾部两部分组成,头部一有棒状的细胞核,核内染色质高度浓缩,细胞核前方有顶体。顶体圆锥状,顶体下腔之中一圆锥状的顶体下锥和细小的囊泡,精子尾部细长,主要由轴丝,致密纤维和线粒体组成,尾部没有波动膜。从蟾蜍科,雨蛙科和蛙科的精子结构看,无尾两栖类在进化过程中,精子结构趋向简单,雨蛙科精子的结