Ultrastructure of muscle cells in Siboglinum fiordicum (Pogonophora)

Two different muscle types are found in the body of Siboglinum fiordicum: body wall muscle and blood vessel muscle. Both are of a myomesothelial type. The myofibrils of the body wall muscle are non-striated and consist of thick and thin myofilaments. Scattered dense bodies and attachment plaques are described. The sarcoplasmic reticulum forms a three-dimensional network in the myofibrils and only peripheral couplings are observed. The thick filaments are of a paramyosin type and have a diameter ranging from 400-1500 A. The blood vessels muscle is non-striated, but sometimes a sarcomere-like organization has been observed. Both thick and thin filaments are present. The thick filaments have a diameter of 250-400 A and lack transverse striations. Dense bodies and attachment of plaques are few. The sparse sarcoplasmic reticulum is restricted to the myofibril periphery where it makes peripheral couplings with sarcolemma. The luminal surface of the vessels is lined by a basal lamina with collagen-like inclusions. No endothelium is found. The body wall muscle and the blood vessel muscle are compared with other muscle types described in invertebrates.     

Pogonophora (Annelida): form and function

Pogonophora, also known as Siboglinidae, are tube-dwelling marine annelids. They rely on endosymbiotic chemoautotrophic bacteria for nutrition and their anatomy and physiology are adapted to their need to obtain both oxygen and reduced sulphur compounds. Frenulate pogonophores are generally long and slender, sediment-living tubeworms; vestimentiferans are stouter, inhabitants of hydrothermal vents and cool seeps; and moniliferans or sclerolinids are very slender inhabitants of decaying wood and sulphidic sediments. The anatomy and ultrastructure of the three groups are compared and recent publications are reviewed. Annelid characters are the presence of chaetae and septa, concentrated at the hind end. The adaptations to a specialised way of life include, in particular, the chitinous tube; the anterior appendages that function as gills; the internal tissue called the trophosome, where the endosymbiotic bacteria live; and the blood vascular system that transports oxygen, sulphide and carbon dioxide to the trophosome.     

Spermatozoon ultrastructure of Xenoturbella bocki (Westblad 1949)

Obst, M., Nakano, H., Bourlat, S.J., Thorndyke, M.C., Telford, M.J., Nyengaard, J.R. and Funch, P. 2011. Spermatozoon ultrastructure of Xenoturbella bocki (Westblad 1949). —Acta Zoologica (Stockholm) 92 : 109–115. Here, we report on the sperm ultrastructure of Xenoturbella bocki (Westblad 1949), which we studied for the first time in detail using light, scanning and transmission electron microscopy. The mature spermatozoa are of the bilaterian primitive type, also called aquasperm and develop as uniflagellate sperm consisting of a round head with distinct mitochondria at the base and a 9+2 flagellum of approximately 42 μm in length. The acrosomal complex consists of a small, round electron translucent acrosomal vesicle and a subacrosomal base. There is no separate midpiece, and the mitochondria surround the proximal and distal centriole in the posterior part of the head. The primitive structure of the spermatozoa suggests that these fertilize the egg by free spawning, probably the ancestral mode of fertilization in early bilaterians. When compared to the spermatozoa of other metazoans, we find that the arrangement of organelles in the Xenoturbella sperm shows similarities to a wide range of protostome and deuterostome taxa and does not seem to indicate any particular phylogenetic relationship.     

A new species of Spirobrachia (Pogonophora) from the Orkney Trench (Antarctica)

Spirobrachia orkneyensis sp. nov. is described from the Orkney Trench to the east of the South Orkney Islands from a depth of 6130–6420 m. It differs from the congeneric species S. grandis (Ivanov 1952) and S. leospira (Gureeva 1975) in the structure of the tube, i.e. shorter segmental collars, peculiarities of their arrangement throughout the tube, and multi-layered, light-coloured tube wall with wrinkles in its inner layers. Also, the wings of the spermatophores of the new species are much larger than those of the two other species of the genus, while most other size characteristics, including the length of the spermatophores, the size of the cuticular plaques, the number of the tentacles and the diameter of the tube, are intermediate between those of S. grandis and S. leospira. A key to the genera and species of the family Spirobrachiidae is provided. Accepted: 31 January 2000     

The Paraspermatic Cell (Atypical Spermatozoon) of Prosobranchia: A Comparative Ultrastructural Study

Melone, G., Lora Lamia Donin, C., Cotelli, F. 1980. The paraspermatic cell (atypical spermatozoon) of Prosobranchia: a comparative ultrastructural study. (Institute of Zoology, University of Milan, Milano, Italy.) — Acta zool. (Stockh.) 61(4): 191–201. The ultrastructure of the paraspermatic cells (atypical spermatozoa) in the male genital tracts of nine species of marine Prosobranchia is described. These cells derive from the same germinal line as the typical spermatozoa, and seem to be homogeneous in their general constitution. In all nine species the paraspermatic cells are characterized by the presence of granules. Axonemes are present in all except one species. Various kinds of paraspermatic cell movements are described; three of the nine species have not yet demonstrated any motility. The significance and the function of paraspermatic cells are discussed.     

Endosymbionts of Siboglinum fiordicum and the phylogeny of bacterial endosymbionts in Siboglinidae (Annelida)

Siboglinid worms are a group of gutless marine annelids that are nutritionally dependent upon endosymbiotic bacteria. Four major groups of siboglinids are known-vestimentiferans, moniliferans, Osedax spp. and frenulates. Although endosymbionts of vestimentiferans and Osedax spp. have been previously characterized, little is currently known about endosymbiotic bacteria associated with frenulate and moniliferan siboglinids. This is particularly surprising given that frenulates are the most diverse and widely distributed group of siboglinids. Here, we molecularly characterize endosymbiotic bacteria associated with the frenulate siboglinid Siboglinum fiordicum by using 16S rDNA ribotyping in concert with laser-capture microdissection (LCM). Phylogenetic analysis indicates that at least three major clades of endosymbiotic gamma-proteobacteria associate with siboglinid annelids, with each clade corresponding to a major siboglinid group. S. fiordicum endosymbionts are a group of gamma-proteobacteria that are divergent from bacteria associated with vestimentiferan or Osedax hosts. Interestingly, symbionts of S. fiordicum, from Norway, are most closely related to symbionts of the frenulate Oligobrachia mashikoi from Japan, suggesting that symbionts of frenulates may share common evolutionary history or metabolic features.     

Ultrastructure of the Geogarypus nigrimanus Spermatozoon (Arachnida,Pseudoscorpionida)

The ultrastructure of the spermatozoon of Geogarypus nigrimanus (Arachnida, Pseudoscorpionida) is described. The spermatozoon is composed of a small elliptic nucleus, a short flagellum and a very long and complex acrosome. In the male genital ducts, as in other studied species of pseudoscorpions, the sperm components are rolled up to form a globular structure enclosed in a cyst wall. The Geogarypus spermatozoon with a reduced flagellum and a giant acrosome seems to be evolutionary more advanced than spermatozoa from other pseudoscorpions.     

Elektronenmikroskopische Untersuchungen am Spermatozoon des Opossum (Didelphys virginiana Kerr)

Summary Spermatozoa from the epididymis of Didelphys virginianaKerr 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.     

Spermatozoon ultrastructure and phylogenetic relationships in the monogeneans (platyhelminthes)

Justine J.-L., Lambert A. and Mattei X. 1985. Spermatozoon ultrastructure and phylogenetic relationships in the monogeneans (Platyhelminthes). International Journal for Parasitology15: 601–608. New observations reported in this study together with bibliographical data allow comparisons of spermatozoon ultrastructure in 28 genera of monogeneans, belonging to 19 families. The authors propose to compare and classify monogenean spermatozoa using two simple ultrastructural characteristics: (a) the number of axonemes, 1 or 2, (b) the presence or absence of cortical microtubules. These traits make it possible to group monogenean spermatozoa in four patterns. Pattern 1 (2 axonemes plus microtubules) is characteristic of the polyopisthocotyleans (9 families). The three other patterns are found in the monopisthocotyleans. Pattern 2 (2 axonemes without microtubules) is found in the Capsalidae and Dionchidae, which seem closely related, and also in the Udonellidae, Gyrodactylidae and Euzetrema. Pattern 3 (1 axoneme plus 1 altered axoneme plus microtubules) is found in the Monocotylidae and Loimoidae. Pattern 4 (1 axoneme without microtubules) is found in the Amphibdellatidae, Ancyrocephalidae, Calceostomatidae and Diplectanidae. A phylogeny of the monogeneans is drawn from the data of comparative spermatology; this scheme coincides in many points with the phylogeny of Lambert (1980) which was based on the study of chaetotaxy and ciliated cells of the oncomiracidium.     

Spermatozoon Ultrastructure in Two Species of Amphibolus (Eutardigrada,Eohypsibiidae)

We examined the ultrastructure of the spermatozoa from two species of eutardigrades, gonochoristic Amphibolus volubilis and hermaphroditic A. weglarskae, by scanning and transmission electron microscopy. The gametes from the two species were morphologically quite similar, each consisting of a short head, neck and tail. The head included a conic, corkscrew-shaped, bilayered acrosome and a cylindrical nucleus with condensed chromatin. The nucleus is surrounded by cytoplasm organized in ovoid elements with an electron-dense core. The neck is very simple, containing a centriole and unmodified mitochondria. The flagellum contains a 9+2 axoneme and terminates in a tuft of between eight and 10 microtubules. The spermatozoa of Amphibolus, like those of the other eutardigrades, are of the modified type, but nonetheless maintain some primitive aspects of the gametes from heterotardigrades.     

Comparative anatomy of excretory organs in vestimentiferan tube worms (Pogonophora, Obturata)

In the past, the excretory systems of only few vestimentiferan species have been examined in detail. This study presents comparative data on eight species on the basis of histological serial sections. Ridgeia piscesae was studied by transmission electron microscopy. All species examined possess a central excretory organ consisting of numerous small branching and intertwined excretory tubules. These are connected to voluminous glandular excretory ducts that lead to the exterior by single or paired excretory pores located at the anterior end of the vestimentum. A comparative analysis shows differences among the species with regard to several features, such as the number of excretory pores, presence/absence of excretory grooves and papillae, position of the excretory organ relative to the brain, and the shape of the excretory ducts. Neither podocytes nor coelomoducts could be detected; therefore, there is no indication of the presence of metanephridia. The vestimentiferan excretory system shows some similarities with the design in Athecanephria (Pogonophora, Perviata) and a general resemblance to the design in sabellid polychaetes, even though in the latter metanephridia are clearly present.     

日本纺织娘的精子超微结构（直翅目：螽斯总科，纺织娘科）

对日本纺织娘Mecopoda nipponensis的精子超微结构进行了透射电镜观察。结果表明：其顶体复合体侧生于细胞核上且包裹了核顶端的部分;细胞核致密,横切面多为新月形或半月形;2蚕豆形副体位于9+9+2轴丝的两侧;线粒体衍生体横切面为椭圆形,其基质几乎完全晶状化;线粒体衍生体一侧的2扁平膜池横切面近S形;轴丝与线粒体衍生体之间有3条连接带,其中中央的一条呈环状;在有些尾部横切面中,质膜之内又有一双层膜把尾部的细胞器围绕起来。     

Ultrastructure of opisthosomal chaetae in Vestimentifera (Pogonophora, Obturata) and implications for phylogeny

Schulze, A. 2000. Ultrastructure of opisthosomal chaetae in Vestimentifera (Pogonophora, Obturata) and implications for phylogeny. — Acta Zoologica (Stockholm) 82 : 127–135
The posterior segmented body region of Vestimentifera bears rows of uncini that function to anchor the animal within its tube. SEM studies of five vestimentiferan species reveal intraspecific and interspecific variation in the number of chaetigerous segments and the arrangement of uncini within a given segment. The portion of an uncinus that extends beyond the epidermis comprises two opposing groups of teeth that probably correspond to the capitium and subrostral process of polychaete uncini, and a distinct protuberance between them, interpreted as a rostrum. In Ridgeia piscesae , the uncini are formed by chaetal follicles, consisting of a chaetoblast, a follicle cell and an epidermis cell. The chaetal shaft is elongate and composed of up to 40 hollow cylinders that are invaded at their base by microvilli from the apical part of the chaetoblast. Opisthosomal chaetae in perviate Pogonophora are usually restricted to four per segment and are of a rod-shaped type. It is hypothesized that the rod-shaped chaetae represent reduced hooked chaetae probably derived from a condition such as found in Monilifera. Uncini of Pogonophora, Sabellida, Terebellida and Oweniida are considered homologous but details of chaetal design may be due to functional adaptations and thus do not represent reliable characters for phylogenetic studies on higher taxonomic levels than genera or potentially families.     

翡翠贻贝精子的超微结构

利用透射电镜研究翡翠贻贝 (Pernaviridis)精子的超微结构。精子为典型的原生型 ,包括头部、中段与尾部三部分。头部由顶体和细胞核组成。顶体明显突出呈倒漏斗形。亚顶体腔呈锥形 ,其中的亚顶体物质呈伞状分布 ,中轴一直延伸至核的后端。细胞核近似球形 ,被管状的核前窝几乎分成相似的两部分。 4～ 5个椭圆形的线粒体围绕着中心粒复合体形成精子的中段。中心粒为中空的圆柱形 ,具有卫星体结构。尾部细长 ,轴丝为典型的“9 2”结构。本文讨论了双壳类精子形态的种属间的差异。     

DNA base composition and genome size of the prokaryotic symbiont in Riftia pachyptila (Pogonophora)

Abstract It has been proposed that Riftia pachyptila , a pogonophoran tube worm abundant at hydrothermal deep sea vents, metabolizes solely via a chemoautotrophic symbiosiols. The symbionts resemble sulfur oxidizing bacteria and form the specific 'trophosome' tissue. Samples of DNA purified from trophosome and vestimentum (muscle) tissues of R. pachyptila were comparatively characterized by thermal denaturation studies, and by analysis of renaturation kinetics. The results show that the great majority of trophosome DNA is homogeneous and prokaryotic with a base ratio of approx. 58 mol% G + C. Its genome size (genetic complexity) is typical of free-living bacteria. Approx. 5% of trophosome DNA appears to be invertebrate DNA equivalent to that found in the vestimentum tissue which lacks symbionts.     

The Spermatozoon of Brachionus plicatilis(Rotifera,Monogononta) With Some Notes on Sperm Ultrastructure in Rotifera

The spermatozoon of B. plicatilisis a thread–like cell with an anterior flagellar portion and a posterior cell body. The flagellum has a lateral ‘undulating membrane’, containing a folded longitudinal cisterna and an axoneme. The basal body of the axoneme is at the anterior tip. The axoneme lacks outer dynein arms and extends through the entire flagellar region and most of the cell body. The main portion of the flagellum and of the cell body contains a series of vesicles with tightly packed tubules that may serve as a cytoskeleton. The cell body contains a partly condensed nucleus, several mitochondria and some cytoplasm. Some elongated mitochondria are arranged in the postnuclear region. When the spermatozoon moves, the undulations propagate from the basal body at the flagellar tip. Late spermatids can be recognized by the nucleus and the flagellum being coiled and enclosed within a common cell membrane. As in other rotifers, there are cigar–like cell products (‘rods’) in the testes. The general organization of the cell, including the absence of an evident acrosome, resembles that of the other known monogonont sperm types.     

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。     

Spermatozoon structure and spermiogenesis in Nassarius kraussianus (Gastropoda,Prosobranchia, Nassariinae)

Summary

The testis of Nassarius kraussianus (Nassariinae) produces two types of spermatozoa, a motile euspermatozoon and a non-motile paraspermatozoon. The euspermatozoon is filiform and about 95/μm long. The elongated head (40 μm long) is comprised of a slender nucleus (about 0.5 μm diameter) which is penetrated throughout by an intranuclear canal housing the anterior portion of the axoneme. A short (about 2 μm long) conical acrosome surmounts the nucleus anteriorly. The mid-piece (23 μm in length) consists of six to seven modified mitochondria which are helically arranged around the axoneme. Posterior to the mid-piece the tail is composed of a short glycogen piece and an end piece. The paraspermatozoon is spindle-shaped (about 50 μm long) and contains multiple (16–20) axonemes the basal bodies of which fuse anteriorly. Posteriorly, numerous small mitochondria and electron-dense bodies lie between the axonemes. Structural changes during eu- and paraspermiogenesis mirror those described for other species of gastropod mollusc with dimorphic spermatozoa. However unlike other molluscs, the cytoplasmic bridges which connect developing spermatids contain well developed stacks of endoplasmic reticulum which form a continuum with that in the cytoplasm of the spermatids. These structures may in some way facilitate the synchronous development of the spermatozoa.