Male occurrence in Austrian populations of Triops cancriformis (Branchiopoda, Notostraca) and ultrastructural observations of the male gonad

Abstract. Recent reports of occasional males in Austrian populations of Triops cancriformis have promoted interest in an analysis of the ultrastructure of the male gonad. It appears as a double thick and well‐defined tubular structure running along the midgut, inside the hemocoel. It is composed of two portions: the wall and the lumen. The former is made up of germ cells that are widespread and intermixed with somatic cells. The lumen is ～200 μm wide and acts as the collecting site of spermatids and sperm. The germ cells are recognizable by their rounded appearance and by the occurrence of exceptionally long synaptonemal complexes in their nuclei. Their maturation implies a volume elongation and an aggregation in a characteristic “cyst” arrangement. The cysts migrate towards the lumen, where they break open, releasing spermatids and sperm. At the end of this process the lumen is filled with maturing gametes. The sperm have very condensed chromatin nuclei and partially reduced cytoplasm where the most striking features are the axoneme and strewn microtubules together with evident pseudopodia. Our morphological data support the full functionality of males in T. cancriformis. However, further work on gametogenesis, distribution of sexes, and genetic analysis of breeding experiments are needed to reach a fuller understanding of the role of males in middle and northern European populations of this species.     

Resorption of unemitted gametes in Lithognathus mormyrus (Sparidae,Teleostei): a possible synergic action of somatic and immune cells

The resorption of unemitted gametes during the post-spawning period of the male and female reproductive cycles in Lithognathus mormyrus was studied by histochemical, histological and cytological methods. The resorption of residual spermatozoa involved the phagocytotic activity of Sertoli cells bounding the seminiferous cysts of spermatozoa, and those associated with spermatogonia lining the lobular lumen. Spermatozoa remaining in the sperm duct were phagocytozed by the lining epithelial cells. Eosinophilic granulocytes and macrophages were identified in the vicinity of residual spermatozoa. The remnants of oocytes underwent an atretic phenomenon in which follicle cells were firstly involved, inducing a progressive fragmentation of the oocyte cytoplasm. Subsequently, eosinophilic granulocytes invaded oocyte degenerative areas and clung to the remaining vitelline inclusions ensuring their biotransformation into waste products (brown bodies). The analogy of the resorption processes of both male and female unemitted gametes during the post-spawning period of natural reproductive cycle, involving first the enveloping somatic cells and then immune cells, is emphasized.     

Ultrastructural observations on the male gametes in Austrognathia sp. (Gnathostomulida,Bursovaginoidea)

The male gametes of the gnathostomulid bursovaginoid Austrognathia sp. were investigated by electron microscopy. All stages of sperm development can be observed in the single saccular male gonad, which is enclosed by a relatively thick basement membrane internally reinforced by thin smooth muscle cells. The spermatogonia are situated close to the testicular theca and produce generally separate primary spermatocytes. From secondary spermatocytes onwards, the nuclear envelope is no longer visible. The spermatids develop synchronously in groups of four, in contrast to arthropod and vertebrate spermatogenesis. A single, large nurse cell, or trophocyte, never observed previously, surrounds each spermatid; perhaps it represents an altered germ cell functioning in nutrition. The spermatid nucleus, initially ovoid, lengthens and takes on the shape of a mushroom head extending into a stalk. Three degrees of chromatin condensation are visible. Anteriorly, a palisade-shaped structure is present just over the highly heterochromatic nuclear zone and is considered to have an acrosome-like function. The outer sperm cytoplasm is characterized by a peripheral tubular labyrinth. Axonemal structures have never been found, but centriole-like structures are present among the medium-density chromatinic strands of the mushroom-like nucleus. No cortical microtubules are evident beneath the cell membrane. The external sperm morphology recalls that of nematode gametes, and some internal features are also similar. Phylogenetic considerations and hypotheses on sperm locomotion are proposed. J. Morphol. 237:165–176, 1998. © 1998 Wiley-Liss, Inc.     

Ionic factors affecting motility,respiration and fertilization rate of the sperm of the bivalvePecten maximus (L.)

Fertilization of the scallopPecten maximus occurs after gametes were naturally released in sea water by the bivalve which has undergone stimulation. The motility of the spermatozoa requires their dilution in sea water (1/40). Dilution triggers an immediate increase of oxygen consumption by sperm, reflecting an activation of a cyanide-sensitive respiration of a cellular origin. When scallops were stimulated by thermal shocks or by serotonin injection, sperm sampled at the urogenital pore output duct shows a respiration-motility activation after sea water dilution which is not seen in sperm scarified from the gonad. Dilution of kidney-sampled sperm into acidic (pH 5) or Na⁺-free artificial sea water reversibly inhibits both respiration and motility. In all cases fertilization rate of sperm is correlated to the increase of respiratory rate and motility measured after dilution in different media. Whether the scallop was stimulated or not, the pH of haemolymph and pericardic fluids were one pH unit below the value of sea water, the pH of the gonad and of the kidney tissues being more acidic (6.5 in average). Our results suggest that the acidic pH of the genital tract maintains the spermatozoa in a quiescent state and that capacitation occurs when male gametes move from the gonad to the kidney from where it is naturally released.Abbreviations ASW artificial sea water - SW sea water - TRIS trishydroxymethyl-aminomethane     

Gonad morphology and sex succession in the protogynous hermaphrodite Hemanthias vivanus (Jordan and Swain)

Hemanthias vivanus , an anthiine serranid common on deep (70–80 m) reefs off eastcentral Florida, is shown to be a protogynous hermaphrodite with observed size ranges as follows: female, 49–77 mm S.L.; transitional 65–74; male, 65–96. Sexes are distinguishable externally as the dorsal spine filaments elongate and colour pattern changes with sex succession. In females, lamellae extend from the lateral and dorsal walls of the bilobed ovary into the lumen. Ova mature within the lamellae and at ovulation pass centrally into the lumen, posteriorly into a common post-ovarian sinus, and exit through the oviduct. Females possess a discrete tissue band (testicular islets) at the border of the alamellar region, from which testicular tissue proliferates during sex succession and replaces the regressing ovarian tissue. In males, spermatozoa are formed in crypts which drain peripherally into a sperm sinus which forms by rupture of muscular and connective tissue layers surrounding the gonad. The sperm sinus drains posteriorly into the vas deferens which is formed by rupture of collagenous tissue surrounding and posterior to the now vestigial post-ovarian sinus. The vas deferens and mesonephric duct join within the urogenital papilla. Two smooth muscle bands associated with the infracarinalis medius muscle bands, the collagenous tissue surrounding the gonoduct, and the intestinal lining are implicated in the extrusion of gametes, urine and faeces. At sex succession, ova are resorbed in one of at least three pathways depending upon their stage of development at the onset of sex transformation: unovulated mature ova become encysted with fibroblasts and invaded by cells of an unknown origin; non-mature yolky ova are invaded and phagocytized by granulosa cells; non-yolky ova are not invaded but fragment.     

Double fertilization in maize: the two male gametes from a pollen grain have the ability to fuse with egg cells

In flowering plants, two male gametes from a single pollen grain fuse with two female gametes, the egg and central cells, to form the embryo and endosperm, respectively. The question then arises whether the two male gametes fuse randomly with the egg and central cells. We investigated this question using two nearly isogenic maize lines with supernumerary B chromosomes (TB10L18) or without (r-tester). B chromosomes regularly undergo non-disjunction at the second pollen mitosis, producing one sperm cell with zero B chromosomes and one with two. We first confirmed earlier studies showing an excess of transmission of the B chromosomes to the embryo rather than to the endosperm. We then tested the possibility of a directed fertilization. For TB10L18 pollen, we could demonstrate the existence of a size dimorphism between the two sperm cells, correlated to the content in B chromosomes, as detected by fluorescence in situ hybridization (FISH). However, no directed fusion of B chromosome containing sperm to egg cells could be detected when using in vitro fertilization. The absence of directed fusion in vitro could also be demonstrated for control lines. We conclude that both male gametes have the capacity to fuse with the egg cell in maize, although sexual reproduction results in a preferential transmission of supernumerary B chromosomes.     

The evolution of gonad expenditure and gonadosomatic index (GSI) in male and female broadcast‐spawning invertebrates

Sedentary broadcast‐spawning marine invertebrates, which release both eggs and sperm into the water for fertilization, are of special interest for sexual selection studies. They provide unique insight into the early stages of the evolutionary succession leading to the often‐intense operation of both pre‐ and post‐mating sexual selection in mobile gonochorists. Since they are sessile or only weakly mobile, adults can interact only to a limited extent with other adults and with their own fertilized offspring. They are consequently subject mainly to selection on gamete production and gamete success, and so high gonad expenditure is expected in both sexes. We review literature on gonadosomatic index (GSI; the proportion of body tissue devoted to gamete production) of gonochoristic broadcast spawners, which we use as a proxy for gonad expenditure. We show that such taxa most often have a high GSI that is approximately equal in both sexes. When GSI is asymmetric, female GSI usually exceeds male GSI, at least in echinoderms (the majority of species recorded). Intriguingly, though, higher male GSI also occurs in some species and appears more common than female‐biased GSI in certain orders of gastropod molluscs. Our limited data also suggest that higher male GSI may be the prevalent pattern in sperm casters (where only males release gametes). We explore how selection might have shaped these patterns using game theoretic models for gonad expenditure that consider possible trade‐offs with (i) somatic maintenance or (ii) growth, while also considering sperm competition, sperm limitation, and polyspermy. Our models of the trade‐off between somatic tissue (which increases survival) and gonad (which increases reproductive success) predict that GSI should be equal for the two sexes when sperm competition is intense, as is probably common in broadcast spawners due to synchronous spawning in aggregations. Higher female GSI occurs under low sperm competition. Sperm limitation appears unlikely to alter these conclusions qualitatively, but can also act as a force to keep male GSI high, and close to that of females. Polyspermy can act to reduce male GSI. Higher male than female GSI is predicted to be less common (as observed in the data), but can occur when ova/ovaries are sufficiently more resource‐intensive to produce than sperm/testes, for which some evidence exists. We also show that sex‐specific trade‐offs between gonads and growth can generate different life‐history strategies for males and females, with males beginning reproduction earlier. This could lead to apparently higher male GSI in empirical studies if immature females are included in calculations of mean GSI. The existence of higher male GSI nonetheless remains somewhat problematic and requires further investigation. When sperm limitation is low, we suggest that the natural logarithm of the male/female GSI ratio may be a suitable index for sperm competition level in broadcast spawners, and that this may also be considered as an index for internally fertilizing taxa.     

Ultrastructure of the gametogenesis of the common Mediterranean starfish,Echinaster (Echinaster) sepositus

Echinaster (Echinaster) sepositus is one of the most abundant sea stars in western Mediterranean rocky bottoms, yet its reproductive biology remains virtually unknown. Here we report the ultrastructure of its gametogenesis over 2 consecutive years. It is a gonochoric species with an annual reproductive cycle spawning gametes in late summer and early autumn. Each arm of every individual contained two gonads (dark red in females and yellow in males). In both sexes, the gonad was a single, large sac composed of several smaller sacs. The gonad wall consisted of two multilayered sacs, outer and inner, separated by the genital haemal sinus. The histology of the gonad wall was consistent with that found in other asteroids. Oogenesis was continuous during the year, but eggs were spawned only in late summer. Oocytes were in close relationship with follicular cells that are suggested to transfer nutrients to the oocytes. Spermatogenesis was restricted to 5–6 months in spring-summer. It occurred in columns with an axial interstitial cell supporting each column, and producing processes towards the lumen that remained connected to spermatogenic cells by intercellular junctions. Developing sperm cells were found along the length of the column, while spermatozoa were found free in the testis lumen. Spermatogenesis followed the pattern described for echinoderms, to give rise to an acrosome-bearing, round-shaped spermatozoon. The histology and cytology of the reproductive process in E. sepositus followed the general pattern found for asteroids.     

Characteristics of the male reproductive system and spermatozoa of leptophlebiidae (ephemeroptera)

This study describes morphological changes in the male reproductive system of Miroculis amazonicus (Savage & Peters) from mature nymphs to subimago stages. The sperm ultrastructure of Massartela brieni (Lestage), Farrodes carioca (Domínguez et al) and Miroculis mourei (Savage & Peters), as well as aspects of cell fragments observed in these species' subimagos deferent ducts were described. Sperm from the three species studied are aflagellated and immotile, while those from F. carioca and Ma. brieni are approximately spherical with a homogenous nucleus and acrosome. Sperm of F. carioca present two or three mitochondria located between the nucleus and the acrosome. In Ma. brieni, only one lateral mitochondria was found. Sperm from Mi. mourei are shaped as a number 'eight', with electron lucent spots inside the nucleus and two mitochondria above the acrosome. Large cell fragments containing degenerative vesicles and some sperm were observed in the deferent duct lumen of the three species. Testes of Mi. amazonicus are extremely reduced in the subimago stage, which suggests that these cell fragments originated from testes degeneration.     

Development of male gametes in flowering plants

The male gametes of angiosperms consist of two sperm cells within a pollen grain or a pollen tube. They are derived from a single generative cell, which is formed as the smaller cell by unequal cell division in the microspore after meiosis. Limited information is available about these male gametic cells, beyond observations by electron microscopy, because each is surrounded by the cytoplasm of a larger vegetative cell. Recently, large quantities of generative cells and sperm cells have been isolated from pollen grains or pollen tubes of various plant species, and their physiological, biochemical and molecular characterization is now possible. Although almost all the available results are still preliminary, it is evident that the male gametic cells are peculiar in terms both of cell structure and composition. For example, they are rich in axial microtubules which maintain the spindle-like shape of each cell. However, they lack plastids which are DNA-containing cytoplasmic organelles. Biochemical characterization of their proteins indicates the presence of male gamete-specific polypeptides. These findings suggest, not unexpectedly, the possibility of male gamete-specific gene expression and of a strict genetic mechanism that controls the formation of male gametes.     

Maternal inheritance of mitochondrial DNA (mtDNA) in the Pacific oyster (Crassostrea gigas): a preliminary study using mtDNA sequence analysis with evidence of random distribution of MitoTracker-stained sperm mitochondria in fertilized eggs

In many bivalve species, paternal and maternal mitochondrial DNA (mtDNA) from sperm and eggs is transmitted to the offspring. This phenomenon is known as doubly uniparental inheritance (DUI). In these species, sperm mtDNA (M type) is inherited by the male gonad of the offspring. Egg mtDNA (F type) is inherited by both male and female somatic cells and female gonadal cells. In Mytilidae, sperm mitochondria are distributed in the cytoplasm of differentiating male germ cells because they are transmitted to the male gonad. In the present study, we investigated maternal inheritance of mtDNA in the Pacific oyster, Crassostrea gigas. Sequence analysis of two mitochondrial non-coding regions revealed an identical sequence pattern in the gametes and adductor muscle samples taken from six males and five females. To observe whether sperm mitochondria were specifically located in the cytoplasm of differentiating germ cells, their distribution was recorded in C. gigas fertilized eggs by vital staining with MitoTracker Green. Although the 1D blastomere was identified in the cytoplasm of differentiating germ cells, sperm mitochondria were located at the 1D blastomere in only 32% of eggs during the 8-cell stage. Thus, in C. gigas, sperm mitochondria do not specifically locate in the germ cell region at the 1D blastomere. We suggest that the distribution of sperm mitochondria is not associated with germ cell formation in C. gigas. Furthermore, as evidenced by the mtDNA sequences of two non-coding regions, we conclude that mitochondrial DNA is maternally inherited in this species.     

Prostaglandins and reproduction of the scallop argopecten purpuratus: II. relationship with gamete release

Levels of prostaglandins E(2) and F(2alpha) were measured in male and female gonadal portions of the functional hermaphroditic scallop Argopecten purpuratus, at the time of spawning. For these measurements, mature scallops were stimulated to initiate their chain of spawning events, and prostaglandins (PGs) were analyzed in samples before stimulation, when animals appeared stimulated to release sperm, during the release of sperm, when animals appeared stimulated to release oocytes, when most of the oocytes had been released, and 24 hr after the end of spawning. The experiment was run twice, once in winter and once in spring. An additional in vitro experiment was carried out to analyze activity of the monoamines dopamine and serotonin on the levels of these prostaglandins. For this, minced tissue of the female portion of the gonad was incubated for different time periods with each of the amines at 10(-5) M. PGs were determined in the tissue samples by radioimmunoanalysis. The results showed that the amounts of the PGs increased significantly in both parts of the gonad during the global process of spawning and decreased when it had been completed. Incubation of minced gonad with the amines affected the time course of PGs variations, i.e., the effect of these compounds depended on the incubation time used. The results support a model for the regulation of spawning which assumes the occurrence of a stimulus which is detected by receptors, processed by nerve cells, and sent to the gonad where intermediation by amines (changing the time course of the process) induces liberation of gametes, in some way modulated by prostaglandins.     

Characteristics of morphogenesis of rudimentary rat gonads transplanted into the testis

The rat embryo (13 and 15 days of development) gonad germs of both sex, as well as isolated primary germ cells (PGC) have been transplanted into testes of mature animals of the same strain and investigated for 1.5 years. The isolated PGC are not able for further development and subjected to reduction. The gonad germs form analogues of the gonads with formation of definitive gonadal cells in 30 days. Further, degeneration of mature gonadal cells takes place. For realization of PGC ++cyto-differential processes and their stage-to-stage transformation into mature gametes certain interactions are necessary with concrete surrounding tissues that are at a strictly synchronized (with germ cells) stages of development.     

Organization of the male gonad in a protogynous fish,Thalassoma bifasciatum (Teleostei: Labridae)

Although the testis in teleosts has been investigated for many years, little attention has been paid to the structure of the outer layers that enclose the testis and to their possible contributions to its organization. The present study in a protogynous male labrid, Thalassoma bifasciatum (bluehead wrasse), describes the arrangement and cytology of these tissues (for convenience, referred to collectively as the outer wall, OW) which include: the outer peritoneal layer and subjacent collagen fibers, myoid cells and diverse other cells and tissues, e.g., fibrocytes, presumptive mesenchyme, macrophages, granulocytes, nerves, and blood vessels. Beneath the OW are two compartments; one is the gamete-laden spermatocysts, the other the interstitium, which is composed of cells and tissues that lie between the spermatocysts. Both OW and interstitium contain similar kinds of tissues and cells. Moreover, the layers of the OW immediately subjacent to the peritoneum are continuous with that in the interstitium. It is suggested that the continuity between these two areas provides opportunities for the exchange of cells that could aid in the maintenance and reorganization of the testis and with the myoid and neural tissue to establish an extensive, coordinated motile system that aids movement of sperm from spermatocysts to the ducts. A recent report on the reexamination of the germinal epithelium concept and its identification in the common snook, Centropomus undecimalis, stimulated us to examine the feasibility of applying this concept to gonad organization and gamete development in T. bifasciatum. In addition, the ultrastructure of the Sertoli cell and formation of spermatocysts are described. Spermatocysts increase in size during the development of gametes. Observations and discussion are presented suggesting how Sertoli cells may accommodate this growth and how new populations of these cells may arise in the mature adult. Finally, ultrastructural characteristics for each stage of spermatogenesis are presented and, using (3H)thymidine and autoradiography, data on the chronology of spermatogonia-sperm cycle are included.     

Functional morphology of the male reproductive system in Callichirus major (Crustacea: Decapoda: Axiidea): Evidence of oocytes in the gonad

Callichirus major inhabits the intertidal region of marine ecosystems and it is frequently used as live bait for fishing. This study aimed to describe the functional anatomy of the male reproductive system by microscopic techniques. The animals were collected along the Corujão beach, Piuma—ES, Brazil, and, in laboratory, the males were classified into two phases: immature (IM) and developed (DE) based on the macroscopic characteristics of the gonads. The gonad and vas deferens were dissected for histological routine and histochemical tests. Histologically, it was noted that in both phases, the more distal region of gonads has ovarian characteristics, showing developing oocytes. Also, different male germ cells were identified: spermatogonium (SPG), spermatocytes I and II (SPTCI, SPTCII), initial and final spermatid (IS, FS) and sperm (SPZ). Accessory cells with spherical or pyramidal nuclei were also present inside the testicular lobules. According to the vas deferens structure, three regions can be characterized: proximal (PVD), middle (MVD) and distal (DVD). In the lumen of the vas deferens, a spermatophoric matrix highly reactive for histochemical tests was observed. The presence of female germ cells in males suggests the occurrence of intersexuality or hermaphroditism in this species.     

Ultrastructure of sperm storage and male genital ducts in a male holocephalan, the elephant fish, Callorhynchus milii.

In chondrichthyes, the process of spermatogenesis produces a spermatocyst composed of Sertoli cells and their cohort of associated spermatozoa linearly arrayed and embedded in the apical end of the Sertoli cell. The extratesticular ducts consist of paired epididymis, ductus deferens, isthmus, and seminal vesicles. In transit through the ducts, spermatozoa undergo modification by secretions of the extratesticular ducts and associated glands, i.e., Leydig gland. In mature animals, the anterior portion of the mesonephros is specialized as the Leydig gland that connects to both the epididymis and ductus deferens and elaborates seminal fluid and matrix that contribute to the spermatophore or spermatozeugmata, depending on the species. Leydig gland epithelium is simple columnar with secretory and ciliated cells. Secretory cells have periodic acid-Schiff positive (PAS+) apical secretory granules. In the holocephalan elephant fish, Callorhynchus milii, sperm and Sertoli cell fragments enter the first major extratesticular duct, the epididymis. In the epididymis, spermatozoa are initially present as individual sperm but soon begin to laterally associate so that they are aligned head-to-head. The epididymis is a highly convoluted tubule with a small bore lumen and an epithelium consisting of scant ciliated and relatively more secretory cells. Secretory activity of both the Leydig gland and epididymis contribute to the nascent spermatophores, which begin as gel-like aggregations of secretory product in which sperm are embedded. Fully formed spermatophores occur in the ductus. The simple columnar epithelium has both ciliated and secretory cells. The spermatophore is regionalized into a PAS+ and Alcian-blue-positive (AB+) cortex and a distinctively PAS+, and less AB+ medulla. Laterally aligned sperm occupy the medulla and are surrounded by a clear zone separate from the spermatophore matrix. Grossly, the seminal vesicles are characterized by spiral partitions of the epithelium that project into the lumen, much like a spiral staircase. Each partition is staggered with respect to adjacent partitions while the aperture is eccentric. The generally nonsecretory epithelium of the seminal vesicle is simple columnar with both microvillar and ciliated cells.     

Development and submicroscopic anatomy of male gametes in Halammovortex nigrifrons (Plathelminthes, Rhabdocoela, ”Dalyellioida”): phylogenetic implications and functional aspects

The steps of spermiogenesis and the submicroscopic anatomy of male gametes in Halammovortex nigrifrons are described. During spermiogenesis the cytophore develops pseudopod-like extensions, and bung-like deposits of dark material become attached to the basal bodies of the cilia. During the phase of cell elongation, cilia stay near the edge of the cytophore. Spermatozoa bear two free cilia or flagella. The axonemata are equipped with glycogen islets appearing at regular spaces. The sperm body is characterized by dot-like dense granules linearly arranged, intense glycogen aggregations in a channel-shaped deposition and giant dense bodies. Events of spermiogenesis and the features of mature male gametes in H. nigrifrons corroborate the hypothesis of the existence of a monophylum within the Rhabdocoela encompassing several, but not all taxa of the ”Typhloplanoida” and ”Dalyellioida”. The Dalyelliidae (including the species of the Temnocephalida) belong to this monophylum.     

Ultrastructure of the male genital tract,spermatogenesis and spermatozoa of hattena cometis domrow (Acari: Gamasida: Ameroseiidae)

The ameroseiid mite Hattena cometis has a male genital system that consists of an unpaired, u‐shaped testis and paired deferent ducts leading into an unpaired accessory genital gland and ejaculatory duct. The genital opening is located anteriorly immediately in front of the sternal shield. Spermatogenesis is simple, probably due to the haploid nature of the male. Eight stages of spermatogenesis could be roughly distinguished. Mature spermatozoa as found in the deferent duct lumen are peculiar in having a bisected nucleus and numerous peripheral flat chambers, which were formed from indentations of the plasmalemma. In inseminated females, spermatozoa were observed in the syncytial tissue of the sperm access system and in the somatic cells of the ovary. These spermatozoa have achieved a new structure, i.e., an electron‐dense plate dividing the cell into two unequal halves. The dense plate has an intricate substructure. Its function is unknown. These sperm cells are considered to represent capacitated spermatozoa. The peripheral chambers are reduced in number inside the female. Similar sperm cells, containing a dense plate, were seen in vacuoles within the epithelium of the deferent duct of one male. These cells are evidently under destruction, but before being completely dissolved had undergone a development leading beyond that of the mature sperm cells found in the deferent duct. Apparently, entering the cell of the deferent duct epithelium or the syncytium tissue triggers the production of the dense plate (or the capacitation process). Our observations are compared with results obtained from other anactinotrichid Acari, mainly Gamasida, and confirm and complete the interpretation of the correlated evolution of components of gamasid reproductive systems. J. Morphol. 274:1010–1025, 2013. © 2013 Wiley Periodicals, Inc.