Spermatic Cysts Research Articles

Reproductive strategies of two invasive sun corals (Tubastraeaspp.) in the southwestern Atlantic

The azooxanthellate sun coralsTubastraea coccineaandT. tagusensisare invasive species which were introduced into Brazilian shallow-water tropical rocky reefs by oil and gas platforms. Both species are simultaneous hermaphrodites and brooders. Histological analysis shows a continuous reproduction with the presence of different stages of development of oocytes, spermatic cysts and larvae occurring together in the same polyps (overlapping). Gametogenesis, embryogenesis, planulation and settlement were observed. Although most of the colonies showed only oocytes, none had only testes. Spermatic cysts were observed in 8.3% ofT. coccineacolonies and in 5.5% of colonies ofT. tagusensis. The maximum diameter of oocyte ofT. tagusensis(1252.5 µm) was greater thanT. coccinea(901.8 µm) and mature spermaries 700 µm in diameter formed the typical arrangement of ‘bouquets’. Although all colonies showed oocytes throughout the year, two reproductive peaks of 3–4 months duration were observed. The larvae ofT. coccineaandT. tagusensishad a competency period of 18 d in aquaria and settled near the parental colony. The investigation of gametogenesis, temporal patterns of reproduction, fecundity and sexual maturation helps to explain the rapid expansion in to new habitats and high population growth in these invasive sun corals.

Sexual reproduction in Sarcotragus spinosulus from two different shallow environments

AbstractThe reproductive cycle of the demosponge Sarcotragus spinosulus from two different shallow environments (La Pierta and La Strea) of the Ionian coasts of Apulia (SE Italy) was studied from February 2006 to February 2007 in 20 tagged specimens. The sponge is viviparous. All the monitored specimens showed sexual reproduction, even if the process usually involved small portions of the sponge tissue. Most of the specimens showed hermaphroditism, with contemporaneous production of oocytes and spermatic cysts in the same reproductive season. Young oocytes occurred from June to September in specimens from La Pierta and from June to October in those from La Strea. Large mature eggs, measuring up to 200 μm, showed a peak in August to September, concomitant with the appearance of spermatic cysts, whose density values were about 100 times higher than those estimated for female elements. At La Pierta, embryos were present for 11 months, whereas at La Strea they were very scarce during the first 4 months of observation, with the results that there was a significant difference in the production of embryos between the two groups of sponges. Embryo development occurred in patches inside the choanosomal region. Cleavage started in September and led in June to a solid stereoblastula, which, only at La Pierta, produced parenchymella larva (371.3 + 31.3 μm on average) from June to July. In the specimens from La Strea, larvae were never observed. The slight differences in the reproductive cycle between the two groups of sponges may be explained in the light of the major variability of the environmental parameters which could have affected the specimens from La Strea negatively.

Sexual reproductive cycle of the epibiotic soft coral Alcyonium coralloides (Octocorallia, Alcyonacea)

Alcyonium coralloides is an epibiotic soft coral overgrowing living colonies of Medi- terranean gorgonians. The main features of the sexual reproductive cycle of this soft coral species are described and quantified for the first time, in a population found at 18 to 22 m depth off the Medes Islands (NW Mediterranean). A. coralloides is a gonochoric internal brooder. The sexual cycle showed a single reproductive event per year. Gametogenesis took 5 to 6 mo, which is the shortest known gametogenesis in littoral octocorals (especially for oogenesis). The maximum mean ± SD diameter was 365 ± 86 µm for spermatic cysts and 632 ± 125 µm for mature oocytes. Sperm was released in spring (late May). Average male and female fecundity in this last phase of the cycle was 15 ± 9 spermatic cysts and 7 ± 4 oocytes per polyp, respectively. Larvae of about 1000 µm in length were observed in the gastrovascular cavities of female colonies in May, before they were released in June. We suggest that the remarkable short gametogenesis and timing shown by A. coralloides is an adaptation to optimize the colonization of its host (in this case the gorgonian octocoral Paramuricea clavata). We conclude that A. coralloides larvae could be ready to settle in early summer when the host P. clavata is probably more vulnerable as a result of its own reproductive cycle coming to an end.

A NGS approach to the encrusting Mediterranean sponge Crella elegans (Porifera, Demospongiae, Poecilosclerida): transcriptome sequencing, characterization and overview of the gene expression along three life cycle stages

Sponges can be dominant organisms in many marine and freshwater habitats where they play essential ecological roles. They also represent a key group to address important questions in early metazoan evolution. Recent approaches for improving knowledge on sponge biological and ecological functions as well as on animal evolution have focused on the genetic toolkits involved in ecological responses to environmental changes (biotic and abiotic), development and reproduction. These approaches are possible thanks to newly available, massive sequencing technologies-such as the Illumina platform, which facilitate genome and transcriptome sequencing in a cost-effective manner. Here we present the first NGS (next-generation sequencing) approach to understanding the life cycle of an encrusting marine sponge. For this we sequenced libraries of three different life cycle stages of the Mediterranean sponge Crella elegans and generated de novo transcriptome assemblies. Three assemblies were based on sponge tissue of a particular life cycle stage, including non-reproductive tissue, tissue with sperm cysts and tissue with larvae. The fourth assembly pooled the data from all three stages. By aggregating data from all the different life cycle stages we obtained a higher total number of contigs, contigs with blast hit and annotated contigs than from one stage-based assemblies. In that multi-stage assembly we obtained a larger number of the developmental regulatory genes known for metazoans than in any other assembly. We also advance the differential expression of selected genes in the three life cycle stages to explore the potential of RNA-seq for improving knowledge on functional processes along the sponge life cycle.

Impact of an invasive alga (Womersleyella setacea) on sponge assemblages: compromising the viability of future populations

The effects of invasive species on native fauna are understudied, even though their consequences should be taken into consideration for the proper conservation and management of marine systems. Furthermore, bioinvasions may have greater consequences if they affect key structural species with slow dynamics such as marine sponges. We propose that reproductive output could be used as a potential early warning signal to detect possible future changes in population trends of long-lived species (i.e. sponges) as a result of biological invasions. The aim of this study was to investigate the effects of invasive algal (Womersleyella setacea) overgrowth on sponge reproduction by comparing the presence of reproductive elements (spermatic cysts, oocytes, embryos, and larvae) in sponges covered by a thick carpet of the invasive algae and in sponges dwelling in the same habitat but without the invasive algae. Three variables were calculated to assess the impact of the invasive alga on sponge reproduction: the reproductive effort, the proportion of individuals in reproduction, and the size of the reproductive structures. We studied eight sponge species representing the main components of the deep rocky reefs of the area. Our results showed that W. setacea had a strong negative effect on sponge reproduction in six out of eight sponge species studied, with lower and even nil reproductive structures on the sponges subjected to the algal overgrowth. Thus, considering that sexual reproduction is necessary for the persistence of most sponge populations, a significant and constant reduction of the reproductive effort may compromise their viability and affect future trends in these benthic systems.

Reproductive demographics, intersex, and altered hormone levels in shortnose sturgeon,Acipenser brevirostrum, from Delaware River, USA

Non-lethal sampling techniques were used to document the reproductive structure of the shortnose sturgeon (Acipenser brevirostrum) population at a fish aggregation site (near Bordentown, New Jersey) in the Delaware River. A total of 68 fish were captured using gill nets (100 × 1.8 m, 12.7 or 15.2 cm mesh) and examined laparoscopically in May–June, and 61 additional fish captured and examined in November during 2006–2011. Six stages of reproductive development were identified in females and five stages were identified in males, encompassing differentiation through maturity in both sexes. Fish captured in the spring were predominantly immature with a higher proportion of females (1 : 1.2 M : F sex ratio), while mature males predominated in the autumn (5.7 : 1 M : F), indicating that the Bordentown area serves as an overwintering/pre-spawn aggregation site. Three distinct forms of intersex were noted in gonads of 11.6% of fish examined: ovo-testis, consisting of scattered spermatic cysts in predominantly immature ovary (3.9%); testis-ova, consisting of ovarian lamellae projecting from a predominantly immature testes (4.7%); and zonal distribution, consisting of multiple, nearly-homogenous pockets of either testicular or ovarian tissues along the gonad (3%). The hormone profile in fish with ovo-testis was similar to that of immature males, while the hormone profile in fish with testis-ova was similar to that of immature females. The relatively high prevalence of intersex raises concerns regarding potential reproductive effects and long-term impacts on shortnose sturgeon in the Delaware River.

Reproductive cycle and larval characteristics of the sponge Haliclona indistincta (Porifera: Demospongiae)

Haliclona indistincta has in some respects, a typical reproductive cycle for a marine haplosclerid sponge. We suggest that oocytes originate from archaeocytes and that spermatozoa originate from choanocytes. Oocytes were first seen in November and matured as eggs by May and June. Immature spermatic cysts were identified from February and mature cysts were present in May and June only. Of the individuals surveyed that had reproductive elements present (150/200), reproductive elements from a single sex were reported in over half of the specimens (59%) but there were also many hermaphrodites (41%). Embryos were first seen in June. Larvae were distributed throughout the mesohyl and were released from the end of June to the end of July. Three mobile larval stages and fusing of sibling larvae were observed. Post-settlement stages from early settlement to the development of oscula and excurrent canals are also shown. However, some elements of the larvae (uniform ciliation and no spicules at posterior pole) are not consistent with larvae from this genus.

High temporal variability in bacterial community, silicatein and hsp70 expression during the annual life cycle of Hymeniacidon sinapium (Demospongiae) in China's Yellow Sea

Hymeniacidon sinapium (De Laubenfels, 1930) (Demospongiae, Halichondrida, Halichondriidae) collected from China's Yellow Sea has been a model sponge species for extensive studies of in vitro cultures of sponge cells and explants in our group since 2002. To better understand its reproductive cycle, the aim of this study is to elucidate the temporal changes in microbial community, the spiculogenesis activity (in terms of silicatein gene expression) and the stress response (in terms of hsp70 gene expression) during its annual life cycle. Histological studies by light microscopy revealed that H. sinapium is a characteristic seasonal species with four distinctive developmental stages of resuscitation, bloom, decline and dormancy during its annual life cycle. The sexual reproductive processes were observed from August to October (summer), with all the reproductive elements (oocytes, sperm cysts, embryos and larvae) documented. There is no direct correlation between seawater temperature and gametogenesis. The gene expression of silicatein and hsp70 was investigated by quantitative real-time RT-PCR during its annual life cycle. Silicatein expression correlated with the histogenesis and reached the highest value in late July (bloom stage). While hsp70 expression correlated with the seawater temperature and also reached the highest value at the same time. We hypothesize that after reaching the maximum biomass growth, sponge should adjust energy distribution to meet the need of gametogenesis and embryogenesis in the reproductive season. Bacterial community variability in a life cycle ranged from 18% to 98% (dice similarity of each two samples) using DGGE, and formed four distinctive clusters consistent with seasons. After sequencing, twelve typical bands from DGGE were compared to GenBank and basically clustered into five phyla: Actinobacteria, α-Proteobacteria, γ-Proteobacteria, Bacteroidetes and Cyanobacteria. This study reported, for the first time, high temporal variability in silicatein, hsp70 and bacterial community during the annual life cycle of H. sinapium. This knowledge is significant for the development of sponge explants culture under controlled laboratory conditions and large-scale sponge seed-rearing technology.

Reproductive cycles of the sympatric excavating sponges Cliona celata and Cliona viridis in the Mediterranean Sea

Abstract. Clionaids are excavating sponges, which live in and grow into calcareous substrates. We studied the sexual reproductive cycles of two clionaid sponges coexisting in a Mediterranean coastal basin (Porto Cesareo, Italy), Cliona viridis and Cliona celata, by analyzing monthly tissue samples of ten specimens of each species collected over a 2-year period. From May to June of the second study year, supplementary samples were taken weekly. Up to 90% of the specimens of C. viridis and 70% of those of C. celata sampled were reproductive during the study. In both species, but particularly in C. viridis, reproductive investment, measured as the percentage of sponge tissue occupied by gametes, was high. Oocytes were present almost year-round in both species, except for a 1–4-month period after zygote release. In contrast, spermatogenesis occurred most frequently in May in both species, when (May–June) oocytes reached their greatest diameters. Cliona viridis and C. celata are hermaphrodites, with oocytes and spermatic cysts coexisting in 10% of the studied individuals in the first year of the study, and in 30% during the second. No developing embryos or larvae were incubated in the sponge tissues, and fertilization was not observed. Temperature may play a role in triggering some important phases of the reproduction of these Cliona, such as oocyte maturation and spermatogenesis, which occurred when water temperature increased from 17°C to 25°C between May and June.

Oogenesis and spermatogenesis in Paraleucilla magna (Porifera, Calcarea)

Gametogenesis in Calcarea is still poorly known; therefore, in this work, we describe the gametogenesis of Paraleucilla magna (Porifera, Calcarea) using light and electron microscopy. Male and female gametes derived from choanocytes. Oocytes grew inside a follicle-like structure composed of pinacocyte-like cells and choanocytes. They were nourished through nutrient transfer from nurse cells and through bacteria phagocytosis, which was never documented for a calcarean species. Mature oocytes were typical, spherical, with nucleolated nuclei and a cytoplasm filled with different types of inclusions and digestive vesicles. Nuage was also found. Spermatogenesis occurred in the lumen of differentiated choanocyte chambers, and spermatic cysts were never formed. Spherical spermatogonia without flagellum or collar were derived from hourglass-shaped primordial germ cells. Spermatozoa were of the ‘aberrant type’, showed a compact electron-dense nucleus and a homogeneous granulated body in its cytoplasm. The gametogenesis of P. magna is similar to what has been observed for other Porifera and Eumetazoa.

Reproductive cycle of the coral‐excavating spongeThoosa mismalolli(Clionaidae) from Mexican Pacific coral reefs

Abstract.Individuals of the recently described demospongeThoosa mismalolliare common on Mexican Pacific coral reefs, excavating burrows in living corals and in other calcareous substrata. To better understand the propagative abilities of this sponge, we conducted a histological study over an 18‐month period (May 2007–November 2008) to identify sexual and asexual reproductive structures. Members of the species are viviparous and hermaphroditic, with various developmental stages of oocytes, spermatic cysts, and embryos co‐occurring in the mesohyl for most of the year. This nearly continuous reproductive activity intensified during the warm season. Fertilization was internal, and embryos developed inside the parental sponge to produce an unciliated hoplitomella larva, characterized by a peculiar siliceous skeleton. In addition to the sexually generated larvae, adults ofT. mismalolliformed gemmules for asexual reproduction. Gemmules occurred within the mesohyl during all months of the year, but were most abundant in the coldest months. This combination of sexual and asexual processes enables individuals ofT. mismalollito reproduce almost continuously. This strategy may facilitate both long‐term persistence within reefs and effective dispersal between distant reefs.

Gamete spawning in Antipathella subpinnata (Anthozoa, Antipatharia): a structural and ultrastructural investigation

Black coral colonies belonging to Antipathella subpinnata (Myriopathidae), found in Adriatic Sea (off the Tremiti Islands) and in Tyrrhenian Sea (Mezzo Canale), were inspected with the aim of investigating their reproductive activity. The small colony (about 42 cm tall) from Adriatic Sea was sexually immature, whereas the larger (about 120 cm tall) five colonies from Tyrrhenian Sea were fertile. Four colonies were males and one was a female, thus confirming the gonochoric condition already known for the black coral. Semithin sections proved that most of the egg and sperm masses flow out through the pharynx, even though small gamete masses were also observed emerging from the tentacles. In the female polyps, egg masses were enveloped by parental tissue derived from the breakage of the mesenterial septa, as observed in the male polyps for the sperm cysts masses. Ultrastructural observations provided details on the characteristics of egg and sperm in this taxon. Sperm stood out for the presence of an acrosome-like structure derived from the merging of pro-acrosomal vesicles. On the whole, the fine organization of the sperm recalled previous descriptions reported for some tropical black coral taxa.

Ultrasonographic Diagnosis of Unilateral Scrotal Hernia, Varicocele and Sperm Granuloma in a Ram

A four-year-old ram was presented with a conspicuous hemilateral scrotal enlargement that was noticed four weeks before. Based on the history, clinical signs, palpation, trans-scrotal ultrasonography and semen collection, a left scrotal hernia was diagnosed. Ultrasonographic examination showed a presumably omental fat scrotal hernia with an atrophic left testis and varicocele, and the presence of two sperm cysts could be observed in the right epididymal tail. The testis appeared as a homogeneous and moderately echogenic structure and it was possible to distinguish atrophy of the left testis that was covered by a hyperechoic area, presumably omental fat, within the hernial sac. In addition, on ultrasound examination non-echogenic tortuous areas were present and diagnosed as varicocele. Post mortem examination confirmed gross lesions identified ultrasonographically. The libido of the ram was normal but the semen showed total azoospermia. Ultrasound imaging can be used as a diagnostic technique to confirm the diagnosis of scrotal hernia, varicocele, sperm cyst and testis mineralization.

Occurrence of somatic cells within the spermatic cysts of demosponges: A discussion of their role

During ultrastructural studies on the spermatogenesis of two demosponges, Raspaciona aculeata and Petrosia ficiformis, somatic cells were detected within their spermatic cysts. In R. aculeata large, amoeboid somatic cells, presumably derived from follicle cells, were found inside cysts filled with secondary spermatocytes. These cells were actively phagocytosing spermatocytes. Such phagocytosis could be directed to eliminate aberrant spermatogenic cells, maintain appropriate cell number within the cysts, or recapture energetic reserves originally allocated to the reproductive process via phagocytosis of spermatocytes. In P. ficiformis, somatic round cells were observed only after the spawning event, phagocytosing unspawned sperm in nearly emptied spermatic cysts. Unlike in R. aculeata, these cells were more similar to archaeocytes (common cells of the demosponge mesohyl with phagocytic activity) than to follicle cells. Phagocytosis of spermatogenic cells and unspawned spermatozoa by somatic cells from the wall of the testes is a well-known process in vertebrates and many invertebrates. Occurrence of somatic cells in the spermatic cysts of sponges, whose function appears to be partially analogous to that of Sertoli cells, reveals that sponges possess cellular mechanisms to regulate testis functioning that are equivalent to those in higher metazoans.

Reproduction in a carnivorous sponge: the significance of the absence of an aquiferous system to the sponge body plan

Sponges usually produce, release, and capture gametes via the aquiferous system, and so the absence of both choanocytes and an aquiferous system in the carnivorous sponge Asbestopluma occidentalis has led to unusual characteristics of development for this Phylum. Sperm are highly specialized elongate cells tightly packed into spermatic cysts in the peripheral tissue of the sponge. Mature spermatozoa have proacrosomal vesicles at the anterior end and a ciliary pit surrounding the flagellum. Clusters of four to five oocytes are in synchronous stages of cleavage, suggesting that fertilization is synchronous. All stages of embryos occur in the same individual. Early cleavage was holoblastic and equal; blastomeres in two-, four- and eight-cell embryos were compact and 16-cell stage embryos were bi-layered. Late-stage embryos show three cellular regions along the anterior-posterior axis: the anterior hemisphere with heterogeneous cells, a mid-region with cells lying perpendicular to the A-P axis in a collagenous matrix, and small cells at the posterior pole. Unusually for Porifera, multiciliated cells cover all but the posterior pole. It is inferred that fertilization occurs by capture of intact spermatic cysts whose surrounding forceps spicules become trapped in the anisochelae of neighboring sponges. The elongate shape of sperm may be designed to penetrate the loose collagenous mesohyl, such that the arrival of a packet of sperm would lead to simultaneous fertilization of oocytes in a cluster. Loss of the water canal system in carnivorous sponges has allowed the evolution of features that are highly specialized for the habitat of this animal, but such modifications were not necessarily a prerequisite for the subsequent evolution of metazoans. Given the extremely versatile mechanisms of gametogenesis, embryogenesis, and tissue/body structure in sponges, generalizations regarding basal metazoan reproduction, development, and structure must be approached with caution.

Embryo development of Corticium candelabrum (Demospongiae: Homosclerophorida)

Abstract. Corticium candelabrum is a homosclerophorid sponge widespread along the rocky Mediterranean sublittoral. Scanning and transmission electron microscopy were used to describe the gametes and larval development. The species is hermaphroditic. Oocytes and spermatocytes are clearly differentiated in April. Embryos develop from June to July when the larvae are released spontaneously. Spermatic cysts originate from choanocyte chambers and spermatogonia from choanocytes by choanocyte mitosis. Oocytes have a nucleolate nucleus and a cytoplasm filled with yolk granules and some lipids. Embryos are surrounded by firmly interlaced follicular cells from the parental tissue. A thin collagen layer lies below the follicular cells. The blastocoel is formed by migration of blastomeres to the morula periphery. Collagen is spread through the whole blastocoel in the embryo, but is organized in a dense layer (basal lamina) separating cells from the blastocoel in the larva. The larva is a typical cinctoblastula. The pseudostratified larval epithelium is formed by ciliated cells. The basal zone of the ciliated cells contains lipid inclusions and some yolk granules; the intermediate zone is occupied by the nucleus; and the apical zone contains abundant electron‐lucent vesicles and gives rise to cilia with a single cross‐striated rootlet. Numerous paracrystalline structures are contained in vacuoles within both apical and basal zones of the ciliated cells. Several slightly differentiated cell types are present in different parts of the larva. Most cells are ciliated, and show ultrastructural particularities depending on their location in the larvae (antero‐lateral, intermediate, and posterior regions). A few smaller cells are non‐ciliated. Several features of the C. candelabrum larva seem to support the previously proposed paraphyletic position of homoscleromorphs with respect to the other demosponges.

Variability in reproductive output across a water quality gradient for a tropical marine sponge

To establish a complete understanding of reproductive variability, larval supply and ultimately population demographics of a species it is important to determine reproduction across a broad spectrum of environmental conditions. This study quantified sexual reproduction of the brooding, gonochoristic sponge Rhopaloeides odorabile from populations across the shelf reefs of the central Great Barrier Reef (GBR). Histological sections of reproductive sponges collected at increasing distances from the coast were used to determine if numbers of reproductive sponges, reproductive output (using a reproductive output index), size at sexual maturity, and sex ratios varied according to their location (distance) from the coastline and therefore from influences of terrigenous/riverine discharge. Significantly higher proportions of reproductive sponges occurred with increasing distance from the coast. The proportion of all reproductive sponges (both male and female) on offshore reefs ranged from 77 to 90%, during November and December, the peak reproductive months of this sponge, compared to 47 to 50% for sponges occurring on coastal reefs. Levels of female reproduction increased with increasing distance from the coastline on two levels. First, oocytes from offshore sponges were significantly larger than oocytes from coastal sponges. Second, sponges from offshore reefs showed a reproductive index (proportions of oocytes, embryos and larvae mm−2) approximately 15 times higher than coastal reef sponges. Therefore, both numbers of oocytes, embryos and larvae in conjunction with larger oocytes contribute to a higher reproductive output index for offshore sponges. The production of spermatic cysts in males was consistent across the GBR. Sex ratios for coastal reef sponges showed a male bias while offshore sponges showed approximate equal sex ratios. The effect of terrigenous riverine input from coastal fluvial plains to the inner GBR is well established and is likely to contribute to the lower levels of reproduction associated with female sponges inhabiting coastal reefs of the central GBR.

Sexual reproduction, larval development and release in Spongia officinalis L. (Porifera, Demospongiae) from the Apulian coast

The reproductive cycle of the bath sponge Spongia officinalis L. has been studied over 1 year on 11 tagged specimens of different sizes (from 82 to 886 ml, in volume) from Ionian coasts of Apulia (SE Italy). According to literature data, the sponge is viviparous. All the monitored specimens showed sexual reproduction, even if the process usually involved small portions of the sponge tissue. Ten specimens were gonochoric (sex ratio 1:1), one specimen showed successive hermaphroditism, with alternate production of oocytes and spermatic cysts in the same reproductive season. Young oocytes occur almost all year round, whereas large mature eggs show a peak in October–November, concomitantly with the appearance of spermatic cysts. No relationships were observed between the sponge size and the presence of sexual elements within the range of the sponge size considered in this research. Embryo development occurs in patches of choanosomal tissue, which contain four or more elements. Cleavage is total and equal; it starts in November and in May leads to a solid stereoblastula, which develops into a parenchymella larva, from May to July. The stereoblastula lacks flagella and its surface is delimited by elongated cells well segregated from the internal ones. Parenchymella larvae are released from June to July, asynchronously, either at the individual or population level, with a few days of de-phasing. Up to 523 larval elements/48 h for a sponge specimen were counted. The free-swimming larvae are ovoid and uniformly flagellated. Flagella are longer at the posterior region, than on the rest of the larval body. Flagellated cells form a pseudo-stratified epithelial layer, delimiting the outermost larval surface, and are filled with electron-lucent vesicles showing a homogenous content. No choanocyte chambers, pinacocytes or skeletal elements are present in the newly released larvae.

Some steps of spermatogenesis in Halichondria semitubulosa (Demospongiae, Halichondriidae)

Spermatogenesis of the marine sponge Halichondria semitubulosa (formerly Pellina semitubulosa) has been investigated at the ultrastructural level. This process can be observed in March when, among the choanocyte chambers of the aquiferous system, spermatic cysts are visible. They are delimited by pinacocyte‐like cells and include elements in progressive development: spermatocytes of the first and second order, spermatids and spermatozoa. The early phase of spermatogenesis was not detected. Spermatocytes of the first order show an elongated shape, several small mitochondria and patched chromatin; spermatocytes of the second order, frequently connected by bridges, show denser chromatin, a single large mitochondrion with numerous tightly adherent cristae, glycogen, and round‐shaped inclusions with a central electron‐dense core. In the spermatids the chromatin tends to be packed in the central region. Spermatozoa have a uniformly dense nucleus in close association with the large mitochondrion. Sperm maturation takes place synchronously within the same cyst but asynchronously within the same specimen.

A 3-year investigation of sexual reproduction in Geodia cydonium (Jameson 1811) (Porifera, Demospongiae) from a semi-enclosed Mediterranean bay

The reproductive cycle of Geodia cydonium in a semi-enclosed Mediterranean bay (Porto Cesareo, SW Apulia) was studied with monthly frequency over a 3-year period. The investigation was carried out by uti- lizing a technique consisting of tagging ten individuals with a PVC stick and cutting oV, by means of a metal cork borer, small samples (cylinders about 5 cm 3 in vol- ume) from each of them for histological analysis. Sex- ual reproductive elements were detected in all individuals, but in the third year some specimens showed reduced reproductive activity or complete infertility. Spermatogenesis occurred in a short period (from June to August) whereas oogenesis lasted longer (from spring to late summer). Spermatic cysts occurred when the frequency of specimens with oocytes reached its maximum values. A relationship between water temperature and the onset of gamete diVerentiation was observed. G. cydonium is here conWrmed ovipa- rous and gonochoric with a sex ratio in favour of the females. However, in contrast with current literature on Porifera—which suggests that only a limited num- ber of sponges, all belonging to the same species are sexually active—the sexual reproduction of this species involves all the examined individuals. This Wnding can be explained by the methodological approach used in this research, which diVers from the traditional way of assessing the sponge reproductive cycle by analysing randomly collected specimens within a population. The study of a series of individuals over time represents a better "model technique" for investigating sponge sex- ual reproduction and the eVect of environmental parameters on gamete diVerentiation.