The ultrastructure of the spermatozoon of Haplotaxis ornamentus (Annelida,Oligochaeta, Haplotaxidae) and its phylogenetic significance

Summary The spermatozoon of Haplotaxis ornamentus has characteristics common to all oligochaete sperm: filiform; primary acrosome vesicle carried on an acrosome tube and containing an axial rod (perforatorium) in an invagination (subvesicular space or secondary acrosomal invagination); an elongate, highly condensed cylindrical nucleus followed by a cylindrical midpiece of radially adpressed mitochondria not penetrated by the axoneme; a single (distal) centriole persistent, though modified, at maturity; axoneme with 9 doublets, each with two outer glycogen granules, and centrally two singlets accompanied by two solid fibres. A peculiar haplotaxid combination of characters (none unique) is slight withdrawal of the primary vesicle into the acrosome tube with a strongly emergent capitulate axial rod and moderately short midpiece. This ultrastructure is consistent with location of the Haplotaxidae at the base of the Haplotaxida (Haplotaxina — Alluroidina — Moniligastrina — Lumbricina). Tubificida sperm, although also plesiomorph for the Oligochaeta, have the autapomorphy elongate periaxial sheath (secondary tube), excepting the Phreodrilidae whose sperm show convergent resemblances to the Lumbricina. The term annuloid has been introduced for annulus-like structures of varied origins.     

The Spermatozoa of the Holothuroidea (Echinodermata): an Ultrastructural Review with Data on two Australian Species and Phylogenetic Discussion

Holothuroidea, like the Crinoidea, Asteroidea and Ophiuroidea have aquatic sperm with a subspherical nucleus in which is embedded a subspherical acrosome and its surrounding periacrosomal material. A ring-shaped mitochondrion behind the nucleus surrounds two centrioles from the distal of which a 9 + 2 axoneme arises. The term "echinosperm" is proposed for this sperm type. Holothuroid echinosperm are characterized by anterior constriction of the periacrosomal fossa; a rounded posterior limit to the acrosome; absence of a distinct subacrosomal depression; outgrowth of a flagellar rootlet from the proximal centriole, of which vestigial homologues are known only in one crinoid and one echinoid. Modified sperm, though not greatly divergent from the echinosperm, are known in two holothuroids and one crinoid. The sperm of echinoids, which are not referable to the echinosperm, are considered plesiomorphic in failure of the acrosome to become embedded in the nucleus (a feature retained from an ancestry shared with enteropneusts), but apomorphic in the conical form of the nucleus and development of spine-like structures around the anterior rim of the nucleus. Spermatozoa1 data suggest that the holothuroid-crinozoan-asterozoan assemblage is the sister group of the Echinoidea. Inclusion of holothuroids in the Echinozoa is not supported.     

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.     

Complex spermatozoon of the live-bearing half-beak,Hemirhamphodon pogonognathus (Bleeker): Ultrastructural description (Euteleostei,Atherinomorpha, Beloniformes)

The spermatozoon of Hemirhamphodon pogonognalhus shows modifications that are frequent though not obligate in internally fertilizing sperm, notably elongation of the nucleus and extension of the mitochondria of the midpiece as an elongate sheath around the proximal region of the axoneme. These similarities to poecilid and jenynsid sperm are considered homoplasic. As in the mature sperm of all but one investigated teleost, an acrosome is absent. The elongate, blade-shaped, electron-dense nucleus has a mean length of 3.2 μm; its basal implantation fossa, less than one-tenth of the length of the nucleus, houses the anterior half of the distal and only centriole (of triplet construction with satellite rays), a centriolar plug, and a mass connecting the centriole to the wall of the fossa. A unilateral putative centriole adjunct is present. The anterior region of the axoneme is surrounded by a mitochondrial sleeve, and internal to this, separated by a cisterna, by a submitochondrial sleeve. The mitochondrial sleeve unites posteriorly with the submitochondrial sleeve. Between the submitochondrial sleeve and the axoneme is a space, the cytoplasmic canal, that is open to the exterior posteriorly. The discrete, cristate mitochondria, in their sleeve, are unique in investigated atherinomorph sperm in being bilateral, grouped on only two opposing sides of the axoneme, with an arc-shaped ‘intermitochondrial link’ between. The 9 + 2 flagellum is unique for the Animalia in having 23 radial subplasmalemmal rods, repeated longitudinally (periodicity 0.025 pm) in a quasicrystalline array. Internal fertilization is deduced to have arisen in the Exocoetoidei independently of that in the Cyprinidcntiformes.     

An ultrastructural analysis of the mature spermatozoon of Anguispira alternata (say) (pulmonata,stylommatophora)

Mature spermatozoa from the hermaphroditic duct of adult snails were examined using various techniques of light microscopy as well as scanning and transmission electron microscopy. The sperm are approximately 557 μm in length including a dextrally spiral head approximately 13 μm long. The head consists of an electron-dense nucleus sculptured into a double-ridged spiral and an acrosome projecting approximately 0.45 μm beyond the apex of the nucleus. The acrosome consists of a membrane-bound vesicle approximately 0.1 μm in diameter and a column of homogeneous material which extends along one side of the terminal spiral of the nucleus. This material is separated from the nucleus by the nuclear envelope. The neck region, though similar to that found in other pulmonates, possesses a unique coiled structure surrounding the central doublet of the axoneme. The midpiece axoneme possesses a 9+9+2 configuration anteriorly grading into a 9+2 pattern for the majority of its length. There are three mitochondrial helices – one primary and two secondary – in the midpiece. Only the primary helix persists throughout the midpiece.     

Organization of the Acrosome and Helical Structures in Sperm of the Aplysiid, Aplysia kurodai (Gastropoda, Opisthobranchia)

Spermiogenesis in the aplysiid, Aplysia kurodai (Gastropoda, Opisthobranchia) was studied by transmission electron microscopy, with special attention to acrosome formation and the helical organization of the nucleus and the other sperm components. In the early spermatid, the periphery of the nucleus differentiates into three characteristics parts. The first part is that electron-dense deposits accumulate on the outer nuclear envelope. This part is destined to be the anterior side of the sperm because a tiny acrosome is organized on its mid-region at the succeeding stage of spermiogenesis. The second part, in which electron-dense material attaches closely to the inner side of the nuclear envelope, is the presumptive posterior side. A centriolar fossa is formed in this part and the axoneme of the flagellum extends from the fossa. A number of lamellar vesicles derived from mitochondria assemble around the axoneme and form the flagellum complex. The third part is recognized by the chromatin which condenses locally along the inner nuclear envelope. During development of the spermatid, this part extends to form a spiral nucleus accompanied by chromatin condensation and formation of microtubular lamellae outside the extending nucleus.
Finally, in the mature sperm, a tiny, spherical acrosomal vesicle is detected at the apex. The slender nucleus, overlapping both the primary and secondary helices which are composed of different structural elements, winds around the flagellum axoneme.     

中国石龙子成熟精子的超微结构

利用透射电镜观察中国石龙子附睾成熟精子的超微结构。顶体囊前部扁平、由皮质和髓质组成 ,穿孔器中度倾斜、顶端尖 ,穿孔器基板塞子状 ,细胞核长形 ,核内小管缺 ,核前电子透亮区小 ,核肩圆 ,核陷窝锥形。颈段具片层结构 ,近端中心粒和远端中心粒的长轴呈直角 ,9束外周致密纤维与远端中心粒相应的 9束三联微管相联 ,向后与轴丝相应的 9束双联微管相联 ,中央纤维与 2个中央单微管相联。中段短 ,多层膜结构缺 ,含有线状嵴的柱状线粒体 ,不规则卵状致密体组成不连续的环状结构 ,纤维鞘伸入中段 ,具终环。线粒体与环状结构的模式为 :rs1 /mi1 ,rs2 /mi2 ,rs3/mi3,rs4 /mi4。主段前面部分具薄的细胞质颗粒区。纤维 3和 8至主段前端消失。轴丝呈“9 2”型。中国石龙子精子超微结构具有塞子状的穿孔器基板、致密体形成不连续的环状结构和纤维鞘始于ms2等特征与巨石龙子群和蜓蜥 -胎生群不同。没有发现石龙子科精子的独征     

The sperm ultrastructure of Caurinus dectes Russell (Mecoptera: Boreidae) and its phylogenetic implications

The sperm structure of the enigmatic mecopteran species Caurinus dectes (Boreidae) is described for the first time. Diagnostic features are the bi-layered acrosome, a cylindric nucleus provided with two longitudinal opposite grooves, and a simple 9 + 2 axoneme which degenerates in the posterior tail end. The results are conform with the monophyly of Mecoptera including Boreidae. A possible autapomorphy of the order is the presence of the two longitudinal opposite grooves along the nucleus, and the presence of two electron-dense fibres beneath the axoneme. Some apparently plesiomorphic features are preserved in the sperm of Caurinus. Features characterizing the distal part of the flagellum, including the presence of an axial cylindrical structure and the distinctive type of axoneme degeneration, are potential synapomorphies of Caurinus and Boreus, i.e. autapomorphic traits of Boreidae.     

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.     

平疣桑椹石磺精子结构观察

通过电光学显微镜和透射电子显微镜观察了平疣桑椹石磺精子的形态及其超微结构。平疣桑椹石磺成熟精子属于进化型,由头部、中段和末段组成。头部由顶体和精核构成,顶体长约0.7μm,呈细奶嘴状,内含物分布均匀,电子密度稍低于细胞核。顶体基部与精核前端紧密相连,无间隙。精核长约3.8μm,宽约1.0μm,核质高度浓缩,电子密度高,无核泡,纵切似辣椒状,核后端内凹形成核后窝。中段加长,结构复杂,线粒体演化成线粒体鞘,螺旋状包绕轴丝。精子末段由轴丝及包绕轴丝的质膜组成,轴丝为典型的“9＋2”结构。比较了平疣桑椹石磺精子与相关腹足类精子结构的异同,进一步证实了腹足纲贝类精子结构之间的区别主要在于顶体有无及形态,精核的长短与外形、中段线粒体的数目及其排列方式等。     

Characteristics of the sperm tail of the velvet worm, Euperipatoides leuckarti (Onychophora)

The onychophoran sperm tail contains several kinds of microtubulcs; probably more than that of any other animal group. There are thus a peripheral manchette consisting of many tightly spaced microtubules, a ring of nine 'peripheral singlets' and a central axoneme of the classical 9 + 2 type (nine doublets and two central singlets). The protofilament organization of these various microtubules was examined and compared to the structure and mode of formation of the peripheral singlets with that of its analogues in other animal groups. The onychophoran peripheral singlets were found to differ in two respects from those in insects: they are formed from the manchette rather than from the axonemal doublets and their transient connection to the axoneme is to the A-subtubules of the doublet rather than to the B-subtubules. The manchette microtubules as well as the peripheral singlets consist of 13 protoh'laments. The manchette may serve a mechanical function (to strengthen the unusually thick sperm tail) hut the role of the peripheral singlets remains unknown.     

The axoneme is involved in the elongation of the spermatid nucleus of Drosophila subobscura

Summary

Our analysis of spermiogenesis of Drosophila subobscura indicates that the axoneme takes part in the elongation of the spermatid nucleus, as follows. In sperm of D. subobscura the axoneme accompanies the nucleus in its full length up to the acrosome. Before the elongation of the nucleus begins, the centriole contacts the nuclear membrane, and is orientated with its axis to the centre of the spherical nucleus. Later in development, at the beginning of nucleus elongation, the axis of the centriole does no longer point to the centre of the nucleus but is dislocated more to one side of the nucleus. Subsequently, the axoneme which is growing from the centriole, pushes the nucleus which develops a cap-like structure over the anterior end of the centriole. By the continuosly growing axoneme stretching forces are applied to the anterior part of the nucleus. Consequently the elongating nucleus gets a smaller diameter anteriorly than posteriorly. And the longer the total length of the sperm is the longer is the nucleus. During elongation the chromatin shows a network-like structure. Nucleus elongation stops when the chromatin is fully condensed but the axoneme continues to grow. Thereupon the cap is no longer seen, and the anterior part of the nucleus which previously was the cap, forms now a bulge beside the centriole and the axoneme.     

Ultrastructure of the spermatozoon of the American Alligator,Alligator mississippiensis (Reptilia: Alligatoridae)

This study details the ultrastructure of the spermatozoa of the American Alligator, Alligator mississippiensis. American Alligator spermatozoa are filiform and slightly curved. The acrosome is tapered at its anterior end and surrounded by the acrosome vesicle and an underlying subacrosomal cone, which rests just cephalic to the nuclear rostrum. One endonuclear canal extends from the subacrosomal cone through the rostral nucleus and deep into the nuclear body. The neck region separates the nucleus and midpiece and houses the proximal centriole and pericentriolar material. The distal centriole extends through the midpiece and has 9 × 3 sets of peripheral microtubules with a central doublet pair within the axoneme that is surrounded by a dense sheath. The midpiece is composed of seven to nine rings of mitochondria, which have combinations of concentrically and septate cristae. The principal piece has a dense fibrous sheath that surrounds an axoneme with a 9 + 2 microtubule arrangement. The sheath becomes significantly reduced in size caudally within the principal piece and is completely missing from the endpiece. Dense peripheral fibers, especially those associated with microtubule doublets 3 and 8, penetrate into the anterior portion of the principal piece axoneme. The data reported here hypothesize that sperm morphology is highly conserved in Crocodylia; however, specific morphological differences can exist between species. J. Morphol. 2011. © 2011 Wiley‐Liss, Inc.     

Spermatozoal Ultrastructure: Evolution and Congruence with a Holomorphological Phylogeny of the Oligochaeta (Annelida)

Plesiomorph characters for the oligochaete spermatozoon are proposed. The chief trends from these plesiomorphies have been elongation of the acrosome and its tube; withdrawal of the primary acrosome vesicle and the axial rod into the acrosome tube and development of a capitulum; development of connectives from the secondary tube to the axial rod (though there is some possibility that the reverse, absence of connectives, is plesiomorph); detorting and shortening of the midpiece (or possibly, again, the reverse) with an increase in numbers of mitochrondria from the plesiomorph four to eight; modification of the base of the tube to form a hen of variable form; and, in one line (lumbricids) flattening of the tip of the nucleus and correspondingly of the limen. Sperm ultrastructure, examined for 9 oligochaete families, corresponds well with taxonomic and phylogenetic groupings recently recognized by the author. However, convergent similarity of the phreodrilid sperm to that of the Lumbricina suggests a corresponding alteration of fertilization biology in the phreodrilids. The results indicate that the Haplotaxidae lie at the base of the opisthopores, though they do not unequivocally contraindicate acceptance of a Haplotaxis-like form as a stem form of the Haplotaxida (opisthopores and Haplotaxidae) and Tubificida. An even more basal position for prosopores, now represented by the Lumbriculida, cannot yet be dismissed.     

FIne structure of the spermatozoon of an onychophoran, Peripatopsis

The spermatozoon of the Onychophoran Peripatopsis moseleyi is described. This cell is characterized by the general filiform shape, the absence of an acrosome, the presence of mitochondrial derivatives, of an annulus and of nine accessory tubules and a manchette of microtubules around the axoneme. All of these characters are typical of highly evolved sperm models, like those of insects and mammals, and suggest a long evolutionary history. Only the position of the mitochondria, inserted between nucelus and axoneme, is reminiscent of annelid features.     

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.     

Ultrastructural observations of spermatozoa of several tetragnathid spiders with phylogenetic implications (Araneae, Tetragnathidae)

The present study reports on the ultrastructure of spermatozoa and spermatogenesis of 12 tetragnathid spiders (10 Tetragnatha species [T. boydi, T. dearmata, T. extensa, T. montana, T. nigrita, T. obtusa, T. pinicola, T. reimoseri, T. shoshone, T. striata]; Pachygnatha listeri and Metellina segmentata). All species develop typical cleistospermia with a coiled nucleus in the center and a coiled axoneme in the periphery of the cell. Remarkable differences in the sperm ultrastructure of the investigated species comprise the shape of the main sperm cell components (nucleus, acrosomal complex, implantation fossa, and centriolar complex). Within the observed Tetragnatha species, three types of sperms were characterized: T. montana-type, T. boydi-type, and T. striata-type. The highly derivative T. montana-type is characterized by the following remarkable features: an extremely elongated nucleus, shaped like a corkscrew and twisted around the axoneme (before coiling); a deep implantation fossa; a corkscrew-shaped acrosomal vacuole; after the coiling process, the nucleus is coiled five to six times in the center of the spermatozoon and the axoneme is coiled five to six times peripheral to the nucleus. The T. boydi-type hardly differs from the T. montana-type, but is remarkable due to the triangular-shaped nucleus (in cross section). The T. striata-type differs especially by a peculiar acrosomal vacuole with a long, slightly curved process and a short appendix, as well as a nucleus that describes only three loose coils around the axoneme (before coiling). The spermatozoa of Pachygnatha listeri and especially Metellina segmentata differ strikingly from the described Tetragnatha-types and are similar to more primitive araneomorph spermatozoa, such as Hypochilus pococki. The described Tetragnatha-types completely correspond with Okuma's (1988a,b, J Fac Agr Kyushu U 32:165-181, 32:183-213) classification of Tetragnatha species. Furthermore, our results suggest an early derivative systematic position of Pachygnatha within Tetragnathinae and the position of Metellina within the Tetragnathidae.     

The spermatozoon of onychophorans. 2. Peripatoides leuckarti

The spermatozoon of the Onychophoran Peripatoides leuckarti is described and compared with that of Peripatopsis previously investigated. The general shape of the cell is the same, with persisting typical characteristic of a manchette and of nine accessory tubules surrounding the axoneme. There is a difference in the mitochondrial derivatives, which are two and partially located in a nuclear posterior concavity. But the most significant finding is the presence of a thin, flat acrosome surrounding the nucleus, which is absent from the other species. The presence of the acrosome is related to the existence in Peripatoides of big eggs, which are absent in Peripatopsis.