The ultrastructure of the spermatozoa of Boa constrictor occidentalis, with considerations on its mating system and sperm competition theories

Sperm ultrastructure has been described for several families of Squamata in which it has been considered a valuable character source for phylogenetic studies. However, sperm competition and mating systems have been demonstrated to influence variations in the sperm morphology and dynamics. The mating system of Boa constrictor occidentalis is likely to have a high degree of sperm competition. We investigated, for the first time, the ultrastructure of the spermatozoa of B. c. occidentalis and, thus, of the family Boidae. Active mating groups were captured from the field, and the spermatozoa of the males was collected by ejaculation and processed to obtain transmission electron micrographs and fluorescence micrographs. The spermatozoa are filiform and their morphology fits the general model described for snakes, and several synapomorphies belonging to the squamates can be identified in these cells. Nevertheless, the head is 25% longer and the midpiece presents a lower frequency of mitochondrial transformations than that of other snakes. We propose that this last trait, along with the extraordinary elongation of the midpiece and the system of multilaminar membranes covering this section (both synapomorphies of the snake spermatozoa), are adaptive responses to processes of sperm competition and sperm storage.     

The ultrastructure of the spermatozoon ofParadynomene tuberculata Sakai, 1963 (Crustacea,Brachyura, Dynomenidae): Synapomorphies with dromiid sperm

The dynomenid spermatozoon, exemplified here byParadynomene tuberculata, resembles the spermatozoa of the Dromiidae, Homolidae and lyreidine raninoids and differs markedly from those of other crabs (the heterotreme, thoracotremes, raninines and raninoidines) in the depressed, discoidal form of the acrosome and the capitate form of the perforatorium. Four or five apparent dynomenid—dromiid sperm synapomorphies are recognizable. (1) Dynomenids (P. tuberculata) and dromiids differ from homolids and lyreidines in the greater depression of the acrosome (ratio of length to width=0.3); (2) the capitate head of the perforatorium is bilaterally prolonged inP. tuberculata as in dromiids though symmetrical in homolids; (3) dynomenid and dromiid sperm lack the—albeit variably developed—posterior median process of the nucleus seen in homolids, anomurans, raninoids and lower heterotremes; (4)P. tuberculata, like dromiids and less distinctly homolids, has an apical protuberance of subopercular material through the opercular perforation, unknown in other crabs, being distinct from the apical button of thoracotreme sperm; (5) a less certain synapomorphy is the anterolateral electron-pale peripheral zone of the acrosome. These synapomorphies endorse a sister-group relationship of dynomenids and dromiids,P. tuberculata sperm differs notably from the sperm of dromiids in the more complex zonation of the acrosome. The perforatorium lacks the radial rays (“spiked wheel”) of homolid sperm and does not show the “amoeboid” form seen in lyreidines. Absence of internal corrugations of the perforatorial chamber is a major difference from all examined raninids. Centrioles are only very tentatively identifiable. Nuclear arms are absent in glutaraldehyde fixed spermatozoa ofP. tuberculata and have not been observed in the dromiidPetalomera lateralis but are present as three small radial vertices in the dromiidDromidiopsis edwardsi and in homolids.P. tuberculata resemblesPetalomera lateralis in the large size of the sperm nucleus relative to the acrosome compared withD. edwardsi and homolids.     

An Ultrastructural Study of Spermatozoa of the Majidae with Particular Reference to the Aberrant Spermatozoon of Macropodia longirostris (Crustacea,Decapoda, Brachyura)

A total of 17 species, in 14 genera of majids have been examined for sperm ultrastructure. The present account describes the sperm of six of these species, in two subfamilies: Pisinae—Sphenocarcinus orbiculatus and Sphenocarcinus stuckiae and Inachinae—Cyrtomaia furici, Grypacheus hyalinus, Platymaia rebierei and Macropodia longirostris. M. longirostris has the only eubrachyuran sperm in which the acrosome is known to depart radically from a subspheroidal form. The acrosome is semilunar in shape and is bordered by a very thin layer of cytoplasm and an unusually uniform, narrow band of chromatin. The apical surface of the acrosome is almost flat, though slightly concave, whereas the posterior surface forms a hemisphere, and is almost completely occupied by the thin, centrally perforate, electron dense operculum. The bulk of the acrosome consists of a homogeneous, moderately electron dense outer acrosome zone. This surrounds a small inner acrosome zone internal to which is an ellipsoidal, pale perforatorium capped by a central acrosome zone. Majid sperm are distinguished by a flattened and/or centrally depressed operculum; a further characteristic is that the pointed perforatorium is relatively short and frequently does not reach the operculum. They vary inter alia with regard to presence or absence of a posterior median process and, apparently, of centrioles and of microtubules in the nuclear arms, and in the number of these arms. Perforation of the operculum, seen in the Pisinae, is not constant in the Inachinae. Spermatozoal ultrastructure offers no certain support for a close relationship of majids with parthenopids or hymenosomatids.     

Consecutive virgin births in the new world boid snake, the Colombian rainbow Boa, Epicrates maurus

Until recently, facultative automictic parthenogenesis within the squamate reptiles exhibiting ZZ:ZW genetic sex determination has resulted in single reproductive events producing male (ZZ) or female (ZW) offspring. With the recent discovery of viable parthenogenetically produced female (WW) Boa constrictors, the existence of further parthenogenetic events resulting in WW females was questioned. Here, we provide genetic evidence for consecutive virgin births by a female Colombian rainbow boa (Epicrates maurus), resulting in the production of WW females likely through terminal fusion automixis. Samples were screened at 22 microsatellite loci with 12 amplifying unambiguous products. Of these, maternal heterozygosity was observed in 4, with the offspring differentially homozygous at each locus. This study documents the first record of parthenogenesis within the genus Epicrates, a second within the serpent lineage Boidae, and the third genetically confirmed case of consecutive virgin births of viable offspring within any vertebrate lineage. Unlike the recent record in Boa constrictors, the female described here was isolated from conspecifics from birth, demonstrating that males are not required to stimulate parthenogenetic reproduction in this species and possibly other Boas.     

Interspecific Variation in Structural Organisation of the Spermatozoon in the Asian Bandicoot Rats,Bandicota Species (family Muridae)

The structural organisation of the spermatozoon from two species of bandicoot rats Bandicota bengalensis and Bandicota indica was investigated by light and electron microscopy together with the effect of incubation in Triton-X 100 and sodium dodecyl sulphate. The sperm head of B. bengalensis is invariably falciform, has a uniform electron-dense nucleus capped by an acrosome with a posteriolateral equatorial segment, a subacrosomal cytoskeleton with a large rostral perforatorium, and a sperm tail, attached to the lower concave surface of the sperm head, with typical coarse fibres and fibrous sheath. By contrast, the sperm head shapes of B. indica are generally conical or bulbous, the nucleus contains a few large vacuoles, the acrosome lacks an equatorial segment, no recognisable perforatorium occurs, and the sperm tail, which is attached basally, is very short with only modest development of coarse fibres and fibrous sheath. These results indicate that, within the genus Bandicota, huge interspecific differences in morphology of the spermatozoon have evolved. The spermatozoa of B. bengalensis are similar to those of Rattus and many other murids and thus presumably represent the ancestral condition, whereas those of B. indica (and B. savilei) are unlike spermatozoa from any other eutherian mammal so far described. © 1998 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd. All rights reserved     

TELEOGRYLUS EMMA精子体外顶体反应的超微结构比较研究

采用相同种类卵水诱导的方法对直翅目,蟋蟀科,黄脸油葫芦的受精囊精子的顶体反应过程进行系统观察.发现黄脸油葫芦精子顶体反应可划分为3个阶段,第1阶段,精子质膜膨胀、断裂或丢失;第2阶段,顶体复合体的顶体外层与顶体本体外膜发生融合,囊泡化;第3阶段,顶体复合体大部分脱落,只留有短锥状的顶体位于核前端.据观察,蟋蟀精子质膜不参与囊泡形成,此结果与家蝇及哺乳类的猪、牛、绵羊、猕猴精子的顶体反应结果很相似.经过比较发现卵水对受精囊内精子的诱导率明显高于精巢内,据分析,可能与精子的生理成熟有关,即便受精囊内精子比精巢内精子更趋于成熟.与其他学者的实验结果相比,蟋蟀精子顶体反应率与家蝇的相似,但明显低于其他动物.这可能与动物的授精方式有关.     

Sperm head structure of a murid rodent from Southern Africa: The red veld rat Aethomys chrysophilus

The morphology of spermatozoa from the red veld rat, Aethomys chrysophilus, of Southern Africa is described; two very different types were found, which came from animals from two separate, as-yet-undescribed, species. In individuals from South Africa the sperm head had a somewhat disc-shaped nucleus and a large acrosome with a huge apical segment that, during epididymal transit, changed in form from initially projecting anteriorly to a highly complex structure that was flexed caudad and lay alongside part of the rest of the sperm head. In addition, the chromatin generally appeared to be not fully condensed. Spermatozoa from animals collected in Malawi were very different in morphology and had a head with a typical apical hook, a perforatorium, fully condensed chromatin, and a 4-μm-long ventral spur. Its sperm tail was also significantly longer. The time of divergence of these two groups of animals from a common ancestor is not known, but the present results show that a considerable morphological change in the sperm nucleus, acrosome, and subacrosomal space can evolve even between two, presumably closely related, species.     

Fine structure of the spermatozoon of <Emphasis Type="Italic">Diopatra neapolitana</Emphasis> (Polychaeta,Onuphidae)

The identification of Diopatra species lacks of clear diagnostic features of taxonomic importance and the knowledge of their reproductive characters is scant. The spermatozoa of Diopatra neapolitana were ultrastructurally investigated by electron microscopy in order to correlate the mode of reproduction with sperm cells morphology. The mature male gamete has a depressed subspherical nucleus, a cone-like acrosome, and a long flagellum. The acrosome is conical in shape and radially symmetrical, with a base diameter twice the height. Within the acrosome vesicle, the basal region includes a very electron-dense thickened ring composed of paracrystalline substances. The subacrosomal space is filled with a poorly electron-dense material, with straight filaments axially arranged to form a perforatorium. The nucleus contains the complete axial canal, holding the hind perforatorium region. The middle piece consists of five mitochondria with well-distinct membranes and tubulo-vesicular cristae. Two centrioles are located perpendicularly to each other. The proximal one lies in the central fossa and the distal one, slightly eccentric to the sperm axis, anchors to the plasma membrane by nine satellite rays of the pericentriolar complex. The axoneme has a 9+2 arrangement of microtubules. In general, the spermatozoon of D. neapolitana conforms exteriorly to the typical ect-aquasperm; the acrosome complex ultrastructure, however, shows noticeable modifications from the basic form. This finding agrees with the previously observed reproductive pattern (broadcast spawning—free-swimming larvae) of D. neapolitana belonging to Santa Gilla population, and may be helpful to solve the taxonomic problems of the D. neapolitana complex as well.     

Parthenogenesis in a Brazilian Rainbow Boa (Epicrates cenchria cenchria)

A 22‐year‐old captive Brazilian rainbow boa (Epicrates cenchria cenchria) gave birth to four offspring after being housed with a vasectomized male. Sexual reproduction as a result of failed prior vasectomy, recanalization of the vas deferens, or prolonged sperm storage was ruled out using the clinical history, histopathology, and gross necropsy. Short tandem repeat (STR) DNA markers were genotyped in the male, female, and four offspring. None of the offspring possessed a diagnostic STR allele present in the potential sire. In addition, all offspring were homozygous at each STR locus evaluated, supporting parthenogenetic reproduction. This is the first report of parthenogenesis in a Brazilian rainbow boa and has implications for the conservation of reptiles maintained in captive breeding programs. Zoo Biol. 32:172–176, 2013. © 2012 Wiley Periodicals, Inc.     

Ultrastructural observations on the spermatozoa of a species of <Emphasis Type="Italic">Lepidodasys</Emphasis> (Gastrotricha,Macrodasyida)

The ultrastructure of the spermatozoon of a species in the marine gastrotrich genus Lepidodasys is described. The filiform cell is composed of a cork-screw acrosome, a long single mitochondrion surrounded by a helical nucleus, and a flagellum with a 9 × 2 + 2 axonemal arrangement. The structure of the sperm of this species from Denmark appears closely similar to those of the other two species of Lepidodasys studied so far from Italy and Florida (US). Peculiar features (cylindrical nucleus, absence of a periaxonemal sheath) place this genus far from the others in the family Lepidodasyidae. The absence of synapomorphies between Lepidodasys and other genera of Lepidodasyidae suggests that the family is polyphyletic. The sperm ultrastructure fully fits the species of Lepidodasys into the marine order Macrodasyida, with the sperm ground plan of which its sperm shares a number of details.     

Sperm Ultrastructure of Tarsius bancanus(Tarsiidae, Primates): Implications for Primate Phylogeny and the Use of Sperm in Systematics

The ultrastructure of the epididymal sperm of Tarsius bancanus is described. The sperm possess the typical eutherian pattern of a dorsoventrally flattened, ovate sperm head, comprising a nucleus capped by a symmetrical acrosome, and a distinct midpiece and principal piece containing a 9 + 9 + 2 arrangement of outer coarse fibres and microtubules. However, unique features are also present. The overall head length (9 μm) equals the greatest for any primate yet examined, and the subacrosomal space ("perforatorium" or "pseudoperforatorium") tilted at 30° to the sagittal axis of the sperm, is described for the first time for mammals. The acrosome extends only a short distance beyond the length of the nucleus of the mature sperm, and a significant reduction in the acrosome to nuclei ratio appears to occur during the final stages of sperm maturation. In contrast to earlier predictions based on the spermatid of Tarsius syrhicta , the mature spermatozoa of Tarsius shows greatest morphological similarity with the sperm of the Anthropoidea, which have a short symmetrical acrosome, than with the Strepsirhini, which have a relatively long acrosome that can be either symmetrical (Lemuriformes) or asymetrical (Lorisiformes). Four proposed phylogenies of the Primates are assessed using comparative sperm ultrastructure. Placing the Tarsiidae as a sister group to the Lorisidae appears the least likely. The sperm data are consistent with the Tarsiidae being a sister group to the Anthropoidea, to the Strepsirhini, or even to the extant primate groups as a whole. Use of sperm morphology to provide characters in phylogenetic systematics of the primates is discussed, and the principle of "total evidence" is preferred to the common practice of "hanging" sperm on phylogenetic hypotheses based on other evidence. © 1997 The Royal Swedish Academy of Sciences. Published by Elsevier Science Ltd.     

Das system der blutkapillaren des auges,insbesondere der brille,von Python reticulatus Schneider 1801, Eryx johnii Russel 1801, Eryx conicus Schneider 1801 und Corallus enydris cooki Gray 1842 (Boidae)

Zusammenfassung Die mit Scribtol injizierten Augen der untersuchten Boidae (Python reticulatus, Eryx johnii, Eryx conicus und Corallus enydris cooki) zeigen im Vergleich zu den Augen aller bisher daraufhin geprüften Colubridae (Natrix natrix, Coluber najadugn, Ahaetulla nasuta und der für these Arbeit gesondert hinzugezogenen Elaphe longissima) eine unterschiedliche, möglicherweise stammesgeschichtlich bedingte Struktur ihres Brillenkapillarnetzes. Während bei den Colubridae bevorzugt eine vertikale Orientierung der langgestreckten Maschen ihres Kapillarnetzes gefunden wird, ist für die Boidae durch die Lage der zu- und abführenden Gefäße eine mehr radiäre Struktur bei weniger gestreckten Maschen kennzeichnend.Die Dichte der Maschen des Kapillarnetzes in dem von den Ocularia freien Brillenteil liegt für Python reticulatus bei 11,4, für Eryx johnii bei 9,2, für Eryx conicus bei 6,3, für Corallus enydris cooki bei 1,8 (!) und für Elaphe longissima bei 11,6 Maschen/mm².Für die untersuchten Arten liegt in dem von den Ocularia freien Brillenteil die Durchschnittszahl der Kapillarmaschen mit einem Quotienten der Koordinatendifferenzwerte (Abszissen- zu Ordinatenwert, Abszisse=Grenze der Supralabialia) 1 und bezogen auf die Gesamtmaschenzahl für Python reticulatus bei 44,1 %, für Eryx johnii bei 36,5%, für Eryx conicus bei 47,1%, für Corallus enydris cooki bei 49,3%, dagegen fur Elaphe longissima bei 20,3%.Die Lage dieser Kapillarmaschen mit einem Quotienten 1 gibt Auskunft darüber, ob ein oder mehrere Sektoren der Brille eine bevorzugte Maschenform aufweisen. Bei dem radiär strukturierten Brillenkapillarnetz von Python reticulatus ist dies im Gegensatz zu dem ähnlich angeordneten von Gekko gecko nicht der Fall.Im proximalen Teil der Aa. chorioideae, d.h. um den Sehnervenaustritt liegt bei Python reticulatus vorwiegend temporal, dorsal und nasal, aber weniger ventral ein relativ großlumiges Gefäßnetz, dessen Maschen verwunden und mehrfach mit der Choriocapillaris verbunden Bind. Fine ähnliche, wenn auch nicht so starke Anastomosenbildung zwischen den Aa. chorioideae und den Aa. ciliares communes nasalis bzw. temporalis wird auch bei Corallus enydris cooki und Elaphe longiwima festgestellt. Die A. ciliaris communis temporalis gibt bei Eryx conicus kurz vor ihrem Übergang in die A. iridis temporalis einen dorsalen und danach einen ventralen, langen diinnen Zweig ab.Die Choriocapillaris von Corallus enydris cooki wird dorsal von fünf bis sechs Abflüssen, ventral von einer V. chorioidea, neben einem an der Sehnervenscheide liegenden Ringgefäß drainiert.

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The eyes, especially the spectacles blood capillary system of Python reticulatus Schneider 1801, Eryx johnii Russel 1801, Eryx conicus Schneider 1801 and Corallus enydris cooki Gray 1842 (Boidae)

Summary Study of the eyes of the Boidae (Python reticulatus, Eryx johnii, Eryx conicus and Corallus enydris cooki) following the injection of Scribtol revealed that the structure of the spectacle capillary network was different from that in Elaphe longissima and the previously investigated Colubridae (Natrix natrix, Coluber najadum and Ahaetulla nasuta), probably due to evolution. While in the Colubridae the orientation of the stretched meshes found in the capillary network is normally vertical, in the Boidae the meshes of the network are typically less tightly stretched and the structure is more radiating, because of the position of the influx and efflux vessels.The density of the meshes of the capillary network in the part of the spectacles not covered by ocularia is 11.4 in Python reticulatus, 9.2 in Eryx johnii, 6.3 in Eryx conicus, 1.8 (!) in Corallus endyris cooki, and 11.6 meshes/mm² in Elaphe longissima.When the quotient of the values for the coordinate difference (abscissa to ordinate value, abscissa=border of the supralabiala) 1 in the species investigated the average number of capillary meshes in the part of the spectacles not covered by ocularia represents in Python reticulatus 44.1% of all the meshes, 36.5% in Eryx johnii, 47.1% in Eryx conicus and 49.3% in Corallus endyris cooki, values significantly higher than the 20.3 % found in Elaphe longissima.The location of the capillary meshes with a quotient 1 provides information as to whether one or more sectors of the spectacles possess a preferred mesh form. With the radiating structure of Python reticulatus this is not the case, however, in contrast to the similar structure found in Gekko gecko.In the proximal part of the Aa. chorioidaea, that is, in the area where the optic nerve leaves the bulbus, there is a relatively wide luminal vessel network in Python reticulatus, this extends slightly in a ventral direction but more in temporal dorsal and nasal directions, and its meshes are twisted and often connected with the choriocapillaris. The vessel network of Corallus enydris cooki and Elaphe longissima was found to be similar, except that not as many connections were observed between the Aa. chorioideae and the Aa. ciliares communes nasalis or temporalis. In Eryx conicus the A. ciliaris communis temporalis has a dorsal branch shortly before it becomes the A. iridis temporalis, and later a long narrow ventral branch. The choriocapillaris of Corallus enydris cooki is drained dorsally by five or six veins, and ventrally by one V. chorioidea and a ring vessel surrounding the sheath of the optic nerve.

     

Aflagellate sperm in three species of leptophlebiidae (Ephemeroptera)

Immotile spermatozoa of 3 species of Ephemeroptera, Habroleptoides umbratilis, Habrophlebia eldae and Choroterpes picteti (Leptophlebiidae) are described. In all 3 species, sperm present a coccoidal shape and lack flagella or microtubule systems. Habrophlebia eldae shows very atypical sperm with a roundish nucleus and scarce cytoplasm, including an apical acrosome. By contrast, a fibrillar perforatorium and a mitochondrion are present in the sperm of H. umbratilis and C. picteti. This latter species also shows electron-dense bodies located in the space between the nucleus and the cell membrane. Our findings suggest that sperm/egg interaction should depend in leptophlebiids on the contraction of the genital duct muscles.     

Caryospora corallae n. sp. (Apicomplexa: Sporozoea, Eimeriidae) from the Emerald Tree Boa Corallus caninus (Serpentes: Boidae)

Oocysts of Caryospora corallae n. sp. were isolated from the feces of three Emerald Tree Boas Corallus caninus. The spherical oocysts of C. corallae averaged 22.4 μn (range 18.7 to 24.6) in diameter and were lacking a micropyle and oocyst residuum; a polar granule was present. The ovoid sporocysts measured 19.1(17.6-20.0) × 13.1(11.7-14.0) μm and a sporocyst residuum and a Stieda body were present. The oocyst wall was approximately 1 μm thick. The sporulation was completed in about 5–6 days at 23 ± 2°C. This is the first report of the genus Caryospora from Corallus caninus a member of the Boidae.     

Salmon: a new autosomal mutation demonstrating incomplete dominance in the boine snake Boa constrictor

An unusual and attractive pigmentation pattern mutation termed "salmon" has been identified in the United States in several captive colonies of the common neotropical boine snake boa constrictor [Boa constrictor (Boidae)]. Boa constrictors expressing the Sa pigmentation pattern appear to be restricted to regions of Panama. Animals with the Sa phenotype exhibit a sharp decrease in melanophore pigments (e.g., melanin) and an increase of xanthophore pigments (e.g., pteridines and carotenoids) throughout the body, including ventral and caudal regions. Moreover, the dorsal saddles (blotches) and lateral diamond patterns are greatly reduced and/or absent. Our study was initiated using a female B. constrictor born in captivity and expressed the Sa pigmentation pattern. Results from breeding experiments indicated an inheritance mode of autosomal incomplete dominance for the Sa and Wt alleles.     

The Ultrastructure of the Spermatozoa of Squamata—I. Scincidae,Gekkonidae and Pygopodidae (Reptilia)

Abstract Squamate autapomorphies seen in sperm of the Scincidae (e.g. Ctenotus robustus, Carlia pectoralis, Cryptoblepharus virgatus, and Lampropholis delicata) are penetration of the fibrous sheath of the axoneme into the midpiece, and the paracrystalline subacrosomal cone. Sphenomorphus group spermatozoa (e.g. Ctenotus) and the Egernia group (Tiliqua) differ from the more derived Eugongylus group (C. virgatus, L. delicata and C. pectoralis) in that the acrosome is elongate and apically depressed; the perforatorium is strongly oblique; the midpiece is relatively short, with four dense ring structures in longitudinal succession; mitochondria are columnar; and enlarged peripheral fibres 3 and 8 do not show the gross anterior enlargement seen in Carlia and Lampropholis. Heteronotia binoei (Gekkonidae) sperm have no epinuclear electron-lucent region; nuclear shoulders are smooth, as in sphenomorph but not Eugongylus group skinks; mitochondria are columnar; unlike skinks, the median surfaces of the mitochondria are indented by triangular, sometimes longitudinally, interconnected dense bodies. In Lialis burtonis (Pygopodidae) sperm, the perforatorium extends virtually to the tip of the fore-shortened apically domed acrosome; nuclear shoulders are absent; the mitochondria alternate singly or in groups with one or more dense bodies which also form an interrupted collar around the distal centriole. Spermatozoal ultrastructure suggests that a common ancestry of snakes and pygopods deserves consideration.     

Is Sperm Ultrastructure Useful in Polychaete Systematics? An Example Using 20 Species of the Fabriciinae (Polychaeta: Sabellidae)

The utility of sperm morphology in the systematics of polychaetes has been questioned in the past. This doubt stems from a problem with methodology, not with sperm morphology. It is argued that sperm characters used in combination with other morphological features have utility at various hierarchical levels. As a test of this proposition males in species from each of the following 10 fabriciin genera: Augeneriella, Fabricia, Fabriciola, Fahricinuda, Manayunkia, Novafabricia, Parafabricia, Pseudofabricia, Pseudofabriciola and an undescribed new Genus A (Fitzhugh et al., in preparation), were examined in order to provide new characters for phylogenetic systematic studies. All species were found to have a dorsal sperm duct running beneath the faecal groove of the thoracic region. No sabellin sabellids or serpulids have this duct. The above Fabriciinae have spermatids developing in large clusters of several hundred cells. Serpulids and sabellins nearly always have sperm developing in tetrads or small groups. Fabriciins studied also have a sperm structure distinct from the Sabellinae and the Serpulidae. Proposed synapomorphies for the members of the Fabriciinae, based on sperm structure, include (1) a thick glycocalyx over the plasma membrane; (2) a distinctive nuclear projection, with an anterior thickening of the nuclear membrane; (3) a thickened. spiraling ridge of nuclear membrane; (4) an extra-axonemal sheath and (5) a unique sheath of mitochondrial material in the midpiece. Within the sub-family there were differences among species in sperm structure. This variability involves acrosome morphology; the structure of the sperm nucleus and nuclear projection; the spiral of thickened nuclear membrane; the structure of the extra-axonemal sheath; the mitochondrial sheath. The monophyly of the Fabriciinae (sensu Fitzhugh, 1991, 1993) is well supported by this analysis. The status of Caobangia is still unresolved and a close examination of this genus is warranted.     

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.