Silica content and spicule size variations in Pellina semitubulosa (Porifera: Demospongiae)

 The variations in both silica content and spicular size were studied in two populations of the demosponge Pellina semitubulosa (Lieberkühn). Samples were collected over a period of 1 year (June 1994 to May 1995) in two Mediterranean coastal basins: Porto Cesareo (southwestern Apulia) and Marsala (northwestern Sicily). The values of spicule size (length and width) and sponge silica content were significantly higher in the population of Porto Cesareo, where the highest water silica concentration was recorded. In both Porto Cesareo and Marsala the sponge silica content showed a seasonal trend, positively correlated with water temperature values. In both populations, the smallest spicules were found in specimens collected from summer to late autumn, after sexual reproduction. Secretion of new spicules may be connected with the process of remodelling occurring in sponges after gamete and larval release. Received: 10 October 1999 / Accepted: 13 April 2000     

Modelling growth forms of the spongeHaliclona oculata (Porifera,Demospongiae) using fractal techniques

The radiate-accretive growth process of the spongeHaliclona oculata, under different environmental conditions, is simulated in a two-dimensional model with fractal modelling techniques. In this model material is added in layers to the object, and growth velocities attain highest values at its protrusions. With this model some aspects of the growth process can be explained. It is possible to simulate thin-branching growth forms, which are normally found under sheltered conditions, and plate-like forms, which are typical for sites more exposed to water movement. These simulated forms are compared with actual growth forms in order to test the validity of the model.     

Predictable annual mass release of gametes by the coral reef sponge Neofibularia nolitangere (Porifera: Demospongiae)

Mass release of gametes of the sponge Neofibularia nolitangere (Duch. & Mich., 1864) occurs simultaneosly along the leeward coast of Curaçao over a period of three subsequent days, without any apparent spatial pattern in the sperad of activity. A population of 99 individual sponges was monitored from August through November 1984 for development and subsequent release of gametes. Release started every day of 3 3-d period (12 to 14 October) at about 1400 hrs and lasted until just after sunset (1830 hrs). Ninety percent of the population showed reproductive activity. Exactly one lunar month later (11 to 12 November), a second release of gametes occurred. In the following year the same sequence of events was observed for the original population (2 to 4 October and 1 to 2 November, 1985). In all instances the first gamete release began on the third day after the full moon. These and earlier observations on this phenomenon show a strong correlation between moon phase and the time of gamete release. Histological and field observations show separate development and release of gametes (sex-ratio males: females 1.5:1) with external fertilization. No sex-reversal occurred in the population during release activity the following year, demonstrating a clear gonochoristic and oviparous type of reproduction for N. nolitangere. First development of oocytes and spermatocytes has been observed at 36 and 7 d, respectively, before the date of first release. In both males and females, a major part of the mesohyl of the total sponge was involved in gamete development. Spermatozoa are released through the osculum as a dense white smoke; eggs consisting of oocyte-nurse cell globules, reinforced with spicules, are separately released en masse with the outgoing water stream of the female sponge. Shortly after release the eggs become sticky and show a negative buoyancy. The reproductive strategy of N. nolitangere appears to be directed at maximizing the number of surviving recruits by maintaining a high reproductive output at a short specific time interval.     

Sessile and non-sessile morphs of Geodia cydonium (Jameson) (Porifera, Demospongiae) in two semi-enclosed Mediterranean bays

Morphological plasticity and ecological aspects of the demosponge Geodia cydonium (Jameson) were studied from seasonal samples collected over 1 year in two semi-enclosed Mediterranean bays of the Southern Italian coast (Marsala lagoon and Porto Cesareo basin). Sponge specimens present two morphs: sessile and non-sessile, both of which showed constant size distribution and density over the studied year. Sessile specimens were larger in size than non-sessile ones. This feature is particularly evident at Porto Cesareo, where these sponges have a more compact skeletal network than at Marsala (evident both in the cortical spicule size and sponge silica content). Sessile specimens adhere to hard rocky substrates (Porto Cesareo) or phanerogam rhizomes (Marsala); non-sessile ones occur on soft bottom areas. Several morphological and structural features of the non-sessile forms differ in the two environments, but the difference in body shape seems to play the most relevant role in enhancing the colonization of incoherent substrates. Indeed, at Marsala, where the large amount of silt and clay determines the occurrence of a markedly reduced anoxic layer just below the surface of the sediment, non-sessile specimens of G. cydonium are fairly spherical and thus able to roll, dragged by slow circular currents. In addition, the usual association with the red alga Rytyphlöea tinctoria, which almost constantly forms a thick and continuous layer around the sponge, allows them to avoid contact with the substrate. The non-sessile specimens from Porto Cesareo inhabit sandy soft bottoms and are flattened. In such an environment, affected by moderate wave turbulence, the flattened shape widens the contact surface between the body and the substrate, thereby reducing the risk of stranding. The evident signs of abrasion, provided by scanning electron microscopy investigations, on both cortical spicules and outermost sponge surface suggest that sponges rub on the bottom. Sediment, epibiontic organisms, and the phanerogam leaves protect this sciaphilous sponge from high solar radiation, allowing the specimens to live in these shallow environments.     

The intrasponge fauna of Spheciospongia vesparia (Porifera,Demospongiae) at Curaçao and bonaire

The infauna of 35 individuals of Spheciospongia vesparia (Lamarck, 1814) of different volumes and from different sites and depths have been inventoried and compared. The number of sponge-inhabiting taxa is logarithmically related to sponge volume. Biomass and total number of the animals contained in the sponge are directly proportional to sponge volume. Numerical and taxonomic composition of infaunas from different sampling sites is fairly constant. Biomass and total number of sponge-inhabiting animals is not significantly different for any of the 4 sampling sites. Several taxa, however, are more abundant in sponges from one or more localities. The ratio of total biomass to total number of intrasponge fauna is found to be significantly smaller for sponges collected in deep water than in shallow water. Differences from and similarities with Pearse's results (1932, 1950) on the infauna of the same sponge species at Dry Tortugas and Bimini are discussed. The relation of the number of contained taxa and the volume of a sponge is compared with the relation of island size and number of taxa present according to MacArthur and Wilson's island-theory (MacArthur, 1972). Finally the erratic occurrence of some taxa as opposed to the highly regular occurrence of some other taxa is discussed. It is concluded that the composition of the sponge-infauna in specimens larger than 11 is highly constant and that the sponge-inhabiting fauna constitutes an ecological community.     

Sexual and asexual reproduction in two species of Tethya (Porifera: Demospongiae) from a Mediterranean coastal lagoon

The sexual and asexual phases of reproductive cycles of two sponges, Tethya citrina and T. aurantium, living sympatrically in a Mediterranean coastal lagoon (Stagnone di Marsala, NW Sicily) were studied from samples collected over an 18-mo period. Both species are oviparous and gonochoric. They have a summer, partially overlapping, period of oocyte production, although T. citrina appear to mature earlier. No males were found, possibly due to the very short period of spermatogenesis. Both species produce asexual buds during the autumn/winter months. However, they seem to follow different reproductive strategies, with T. citrina showing a significantly lower production of buds than T. aurantium; by contrast, egg production is significantly lower in the latter species. The difference in the reproductive resource allocation is consistent with data reported in the literature on the anatomy features, genetic population structure and ecological distribution.     

Unravelling host and symbiont phylogenies of halichondrid sponges (Demospongiae, Porifera) using a mitochondrial marker

We present the first comparative phylogenetic analysis of a selected set of marine sponges and their bacterial associates. The Halichondrida form an important order in demosponge systematics and are of a particular interest due to the production of secondary metabolites. We sequenced a fragment of the cytochrome oxidase subunit 1 (CO1) gene of the sponges and their bacterial associates, compared the reconstructed phylogenies and found evidence for radiation in coevolution. The tree of six host-species associations showed four supported cospeciation events between the sponges and the bacteria. In addition, we present the first gene tree of sponges based on a mitochondrial marker. The tree shows major congruences with previous morphological studies and suggests the applicability of a mitochondrial marker in sponge molecular systematics.     

Pigments of the Porifera: Demospongiae. I. Carotenoids of Axinella verrucosa

Studies were made of some carotenoids extracted from Axinella verrucosa (O. schmidt) (Porifera: Demospongiae), a species which occurs in the Gulf of Naples. -carotene, renieratene, isorenieratene, and an unknown isomer of renieratene have been isolated.     

Genetic, morphological, and chemical divergence in the sponge genus Latrunculia (Porifera: Demospongiae) from New Zealand

We undertook a comprehensive study of Latrunculia in New Zealand to determine the relationship between taxonomic, environmental, and chemical variation within the genus. Sponges were collected from five locations around New Zealand: Three Kings Islands, Tutukaka, Wellington, Kaikoura, and Doubtful Sound. Allozyme electrophoresis at nine polymorphic loci indicated that sponges from each geographic location were genetically distinct, and that they displayed genetic differences of the magnitude usually associated with reproductively isolated species (Nei's D between locations =0.375-2.476). Additionally, the comparisons revealed that the green and brown colour morphs of Latrunculia that are sympatric at Three Kings Islands and Kaikoura are distinct from each other, and that there are two genetic groups within the green sponges in Doubtful Sound. On the basis of genetic data we conclude that there are at least eight species of Latrunculia in New Zealand waters, not one to four as had been previously thought. Morphological comparisons of the eight genetic species based on skeletal characters (i.e. skeletal organisation of the choanosome, spicule composition, size, and geometry) indicated that the eight Latrunculia species fell into only two morphological groups that could be easily diagnosed on the basis of discorhabd type. Within these two primary morphological groups, skeletal characteristics among the eight species largely overlap and are not diagnostic. These findings emphasise the limitations of traditional taxonomic methods based solely on skeletal characters for distinguishing species of Latrunculia. However, multivariate analysis (MANOVA and CDA) based on six measured skeletal variables did reveal significant morphological variation among the species (Pillai's Trace=3.28, F=6.90, P<0.0001), supporting the division of the genus into eight species. Comparisons of chemical extracts from Latrunculia also showed that the amounts of five different bioactive compounds (discorhabdins A, B, C, D, and J) varied predictably among the eight species. This finding suggests that discorhabdin variation within Latrunculia, previously thought to be associated with intra-specific environmental variability, is more likely to reflect differences among species rather than phenotypic plasticity. Our results also highlight the importance of thorough taxonomic studies associated with marine natural products research to understand fully the variation in bioactive properties among individuals. The potential processes underlying the unusually high speciation rates in New Zealand Latrunculia that are indicated in our study are discussed.     

N-acyl homoserine lactone production by bacteria within the sponge Suberites domuncula (Olivi, 1792) (Porifera, Demospongiae)

Many bacteria live in close association with sponges. Within these consortia, molecules of communication such as quorum-sensing and hormone-like molecules may occur in order to regulate the partnership. Of particular interest, bacterial N-acyl-l-homoserine lactones (AHLs) were screened in supernatants from Suberites domuncula-associated bacteria using an E. coli bioluminescent reporter system. These sponge-associated bacteria were beforehand isolated on several media supplemented or not with a sponge extract to attempt to isolate sponge-specific bacteria. Out of 81 AHL-producing bacteria, three strains requiring sponge extract to grow were selected for AHL characterization. The in vitro produced AHLs, that is, in bacterial culture supernatants, were identified as N-(3-butanoyl)-l-homoserine lactone and N-(3-oxododecanoyl)-l-homoserine lactone and quantified using LC–ESI–MS/MS. The in vivo production of AHLs by sponge-associated bacteria has also been demonstrated in a healthy host for the first time: N-(3-oxododecanoyl)-l-homoserine lactone, N-(3-hexanoyl)-l-homoserine lactone, and N-(3-heptanoyl)-l-homoserine lactone. This AHL production in sponges may suggest a potential role of these molecules between sponge-associated bacteria and/or between sponge-associated bacteria and the sponge.     

Carotenoid patterns in twenty-nine species of sponges in the order Poecilosclerida (Porifera: Demospongiae): a possible tool for chemosystematics

We assessed the utility of separated carotenoid mixtures for sponge systematics. Carotenoids were extracted from 29 species of 22 genera of 6 families for the demosponge order Poecilosclerida. Mixtures were separated (by thinlayer chromatography on silica gel) without chemical modification and after alteration by saponification, reduction or acetylation or a combination thereof. This approach allowed analysis of individual colonies of less than 1 g wet weight. Relationships among taxa were determined through use of Lawson's similarity index and discriminative analysis. Analysis of multiple runs of fractions from one individual of Ophlitaspongia pennata showed the method to be consistent and reliable. Comparison of specimens of species collected at different localities and times showed high correspondence of carotenoid patterns except in those species suspected of representing species complexes. Analysis of members of the family Clathriidae and of relationships within the order Poecilosclerida suggest that fatty acids esterified to carotenoids may be family-specific and of more taxonomic value than carotenoids. The importance of testing for seasonal, geographic and habitat variability in biochemical patterns is stressed. We discuss the significance of these methods to sponge systematics and their use in comparative studies.     

Location of toxicity within the Mediterranean sponge Crambe crambe (Demospongiae: Poecilosclerida)

Within-specimen location of toxicity in Crambe crambe (Schmidt) has been addressed by complementary procedures on specimens collected in north-east Spain (Western Mediterranean) in winter of 1993. The toxicity of the distal (ectosome) and basal (choanosome) sponge parts have been analysed and the main cellular types present in these two layers have been studied by light and electron microscopy. The toxicity of the three main cell types, separated by the gradient-density method, has also been analysed. Three main fractions, each of them enriched in a different cellular type, were obtained: Fraction 1 (interface between 2 and 5% Ficoll) contained 90±0.9% (mean±SE) of spherulous cells and 10% of different cell types consisting of choanocytes (5±0.54%), and unidentified cells or cell debris (5±0.84%); Fraction 2 (interface between 5 and 8% Ficoll) was enriched in choanocytes (70±0.95%), and also contained spherulous cells (11.8±0.73%), archeocytes (6.2±0.74%) and unidentified sponge cells (12±0.74%); Fraction 3 (interface between 8 and 11% Ficoll) mainly consisted of archeocytes and archeocyte-like cells (75±0.66%), together with spherulous cells (7±0.74%) and other unidentified sponge cells and cell aggregates mainly formed by choanocytes (18±0.41%). Toxicity [measured in toxicity units, TU, using the Microtox^® procedure] was significantly higher in the sponge ectosome (12.45±1.4 TU) than in the choanosome (2.58±0.92 UT). Only the abundance of spherulous cells in the sponge tissues correlated well with the pattern of toxicity observed, and this was corroborated by the toxic behaviour of the three cellular fractions obtained: the one enriched in spherulous cells was highly toxic (9.08 UT), whereas those enriched in choanocytes and in archeocytes were almost inactive (0.48 UT) or totally innocuous, respectively. All these results point to the spherulous cells being responsible for the storage (and possibly production) of the toxic compounds in C. crambe. Toxicity is concentrated in the sponge periphery. Spherulous cells are also concentrated in this area and can also be observed outside the sponge exopinacoderm. These results correlate well with the assumption of a defensive role of toxicity, since encounters with potential epibionts, predators and competitive neighbours take place through this peripheral zone. However, we found two types of spherulous cells (orange and colourless, respectively) coexisting in the same sponge zones as well as in Cell Fraction 1. Thus, we cannot at present determine whether one or both types are responsible for the toxicity encountered, although it is likely that the two correspond to different states of the same cell type.     

Reproductive strategies and diet in deep-sea nuculanid protobranchs (Bivalvia: Nuculoidea) from the Rockall Trough

Although the taxonomy of deep-sea protobranch bivalves is becoming better known, relatively little information is available on their reproductive biology and whether or not populations show reproductive periodicities. We have examined the reproductive biology of three common sympatric species as part of a long-term time-series of samples taken from 2900 m in the Rockall Trough from 1973 to 1983. Malletia cuneata Jeffreys, 1876 produces a maximum of 30 oocytes at any one time and these grow to a maximum size of 240 m. Maximum fecundity of Ledella pustulosa (Jeffreys, 1876) and Yoldiella jeffreysi (Hidalgo, 1877) is 174 and 360, respectively, and both species produce an egg of 120 m in diameter. These data indicate lecithotrophic early development in L. pustulosa and Y. jeffreysi, but direct development in M. cuneata; however, evidence from the prodissoconch length of M. cuneata suggests lecithotrophic development. L. pustulosa and Y. jeffreysi also differ from M. cuneata in having a distinct reproductive cycle with spawnout in the winter months. Both the continuously breeding M. cuneata and the seasonally breeding L. pustulosa ingest diatoms, coccoliths and foraminiferans, but whereas the diet of M. cuneata appears to be constant throughout the year there is an apparent reduction in the feeding activity of L. pustulosa concomitant with the deposition of phytodetritus on the deep-sea bed.     

Genetic differentiation between morphotypes of the marine sponge Suberites ficus (Demospongiae: Hadromerida)

Sponges of three morphotypes of Suberites ficus (Johnston, 1842) were collected during February and March 1985 off the south-west of the Isle of Man, and were compared by using spicule size distributions and genetic allele frequencies of isozyme loci. The populations did not show any significant differences of spicule size or type, but could be easily differentiated into three separate species based on isozyme patterns. Samples of pale orange S. ficus growing on gastropod shells inhabited by hermit crabs (Pagurus spp.) were reproductively isolated from the redorange and the pale yellow colour morphs encrusting the bivalve Chlamys opercularis. These latter two colour morphs were genetically similar, but significant differences were observed at two of the 19 gene loci assayed. All the sponges studied were sympatric, and therefore the genetic differences, indicating reproductive isolation, are strong evidence for separate gene pools and, hence, that they are different species. The genetic identity between the two colour morphs of S. ficus on C. opercularis shells was 0.977, whilst between each of these and S. ficus on hermit crabs it was about 0.65. In all three species genetic variability was high, with mean expected and observed heterozygosity values per locus ranging from 0.17 to 0.36.     

Reproductive strategies of two deep-sea gastropod species from the Porcupine Seabight (Northeast Atlantic)

Two species of small gastropods (<6 mm in length), Amphissa acutecostata (Philippi, 1844) and Gymnobela subaraneosa (Dautzenberg and Fischer, 1896), widely distributed in the northeast Atlantic, were found in large numbers in the Porcupine Seabight (Northeast Atlantic). Except for some aspects of taxonomy and distribution, as well as some data on larval development, the biology of these species is unknown. This study describes basic aspects of the life-history strategies of both species. Histological studies showed that oocyte and sperm development in both species was similar to the gametogenetic patterns observed in other deep-sea gastropods. In females, oogonia proliferated in the germinal epithelium and developed into previtellogenic oocytes (30–40 m), which grew into vitellogenic primary oocytes. Vitellogenic oocytes were covered by a thin layer of follicle cells involved in the vitellogenic processes. The maximum size for mature oocytes was 99.06 m for A. acutecostata and 114.82 m for G. subaraneosa. In A. acutecostata most of the volume of the ovary was occupied by previtellogenic and early vitellogenic oocytes, whereas in G. subaraneosa most of the volume was filled by large vitellogenic oocytes. Both species showed quasi-continuous production of oocytes. The oocyte size-frequency diagrams suggested a continuous release of a small number of oocytes throughout the year for A. acutecostata, and asynchronous periodic spawning events for G. subaraneosa. Gonad development and gametogenesis could be strongly affected by presence of parasites in one of the populations of G. subaraneosa.Communicated by J.P. Thorpe, Port Erin     

Asexual reproduction in homoscleromorph sponges (Porifera; Homoscleromorpha)

Asexual reproduction by external budding in Homoscleromorpha is reported for the first time. Two Mediterranean sponge species were studied, Oscarella lobularis and O. tuberculata. Buds are formed in the marginal basal part of sponge. Budding takes from 1 to 4 days and is defined in three budding stages. First, small irregular protuberances, consisting of external parental tissue, are formed. Second, they elongate and acquire more regular, nipple-like shape. These protuberances are tube like, their internal cavity derived from parental exhalant canal. The wall consists of three layers: (a) external layer is flagellated exopinacoderm, (b) internal one is flagellated endopinacoderm and (c) intermediate one is a thin layer of mesohyl. Third, a spherical bud with a large central cavity is formed. During budding, we did not observe cell proliferation or transdifferentiation either in budding zone or in any special mitotically active region. The bud attached to the substrate is similar to the rhagon developing after larva metamorphosis, it has a syconoid organization. Morphogenetically, budding in Oscarella differes from that in other sponges. Occurring by epithelial morphogenesis, it is similar to morphallaxis during regeneration. The presence in Homoscleromorpha of an epithelial morphogenesis is unique among sponges. This feature is shared by Homoscleromorpha and Eumetazoa.     

A 3-year investigation of sexual reproduction in <Emphasis Type="Italic">Geodia cydonium</Emphasis> (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 utilizing a technique consisting of tagging ten individuals with a PVC stick and cutting off, by means of a metal cork borer, small samples (cylinders about 5 cm³ in volume) from each of them for histological analysis. Sexual 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 differentiation was observed. G. cydonium is here confirmed oviparous 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 number of sponges, all belonging to the same species are sexually active—the sexual reproduction of this species involves all the examined individuals. This finding can be explained by the methodological approach used in this research, which differs 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 sexual reproduction and the effect of environmental parameters on gamete differentiation.     

Morphological evidence for vertical transmission of symbiotic bacteria in the viviparous sponge<Emphasis Type="Italic"> Halisarca dujardini</Emphasis> Johnston (Porifera,Demospongiae, Halisarcida)

All stages of vertical transmission of symbiotic bacteria, from the penetration into oocytes to the formation of rhagon, were investigated in the White Sea (Arctic) representatives of Halisarca dujardini Johnston (Demospongiae). Small populations of free-living specific symbiotic bacteria inhabit the mesohyl of H. dujardini. They are represented by a single morphotype of small spiral gram-positive bacteria. Vertical transmission of symbiotic bacteria between generations in sponges may occur in different ways. In the case of H. dujardini the bacteria penetrate into growing oocytes by endocytosis. A part of the bacteria plays a trophic role for oocytes and the other part remains undigested in membrane-bound vacuoles within the cytoplasm. In cleaving embryos bacteria are situated between the blastomeres or in the vacuoles. In the blastula all bacteria are disposed in the blastocoel. The symbionts are situated in intercellular spaces in free-swimming larvae and during metamorphosis. Symbiotic bacteria do not play any trophic role in the period of embryonic and postembryonic development of H. dujardini. No signs of destruction and digestion of bacteria were revealed at any stage of development.Communicated by O. Kinne, Oldendorf/Luhe     

Reproductive behaviour ofNereis diversicolor (Annelida: Polychaeta)

Nereis diversicolor O. F. Müller, collected on the tidal flats of the Jadebusen (North Sea, FRG) in autumn 1987 and 1988, was exposed to different temperatures in the laboratory. Results indicated that maturation was induced by temperatures above 6°C; spawning in early spring was synchronized by raising temperatures after a period of low temperatures in winter, and occurred mainly at new and full moon. During reproduction the female stays inside the burrow; the male releases sperm in front of it; the resultant larvae remain in the tube for 10 to 14 d protected by the female.     

Sexual reproduction,larval development and release in <Emphasis Type="Italic">Spongia officinalis</Emphasis> 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.