Ostreidae Research Articles

OysterDB: A Genome Database for Ostreidae.

The molluscan family Ostreidae, commonly known as oysters, is an important molluscan group due to its economic and ecological importance. In recent years, an abundance of genomic data of Ostreidae species has been generated and available in public domain. However, there is still a lack of a high-efficiency database platform to store and distribute these data with comprehensive tools. In this study, we developed an oyster genome database (OysterDB) to consolidate oyster genomic data. This database includes eight oyster genomes and 208,923 protein-coding gene annotations. Bioinformatic tools, such as BLAST and JBrowse, are integrated into the database to provide a user-friendly platform for homologous sequence searching, visualization of genomes, and screen for candidate gene information. Moreover, OysterDB will be continuously updated with ever-growing oyster genomic resources and facilitate future studies for comparative and functional genomic analysis of oysters ( http://oysterdb.com.cn/ ).

Dominance of transposable element-related satDNAs results in great complexity of “satDNA library” and invokes the extension towards “repetitive DNA library”

Research on bivalves is fast-growing, including genome-wide analyses and genome sequencing. Several characteristics qualify oysters as a valuable model to explore repetitive DNA sequences and their genome organization. Here we characterize the satellitomes of five species in the family Ostreidae (Crassostrea angulata, C. virginica, C. hongkongensis, C. ariakensis, Ostrea edulis), revealing a substantial number of satellite DNAs (satDNAs) per genome (ranging between 33 and 61) and peculiarities in the composition of their satellitomes. Numerous satDNAs were either associated to or derived from transposable elements, displaying a scarcity of transposable element-unrelated satDNAs in these genomes. Due to the non-conventional satellitome constitution and dominance of Helitron-associated satDNAs, comparative satellitomics demanded more in-depth analyses than standardly employed. Comparative analyses (including C. gigas, the first bivalve species with a defined satellitome) revealed that 13 satDNAs occur in all six oyster genomes, with Cg170/HindIII satDNA being the most abundant in all of them. Evaluating the “satDNA library model” highlighted the necessity to adjust this term when studying tandem repeat evolution in organisms with such satellitomes. When repetitive sequences with potential variation in the organizational form and repeat-type affiliation are examined across related species, the introduction of the terms “TE library” and “repetitive DNA library” becomes essential.

The complete mitochondrial genome of Hyotissasinensis (Bivalvia, Ostreoidea) indicates the genetic diversity within Gryphaeidae.

Different from the true oyster (family Ostreidae), the molecular diversity of the gryphaeid oyster (family Gryphaeidae) has never been sufficiently investigated. In the present study, the complete mitochondrial (mt) genome of Hyotissasinensis was sequenced and compared with those of other ostreoids. The total length of H.sinensis mtDNA is 30,385 bp, encoding 12 protein-coding-genes (PCGs), 26 transfer RNA (tRNA) genes and two ribosomal RNA (rRNA) genes. The nucleotide composition and codon usage preference of H.sinensis mtDNA is similar to that of H.hyotis within the same genus. On the other hand, the presence of three trnM and three trnL genes of H.sinensis was not detected neither in H.hyotis nor other ostroid species. Another unique character of H.sinensis mtDNA is that both rrnS and rrnL have a nearly identical duplication. The PCG order of H.sinensis is identical to H.hyotis and the two congener species also share an identical block of 12 tRNA genes. The tRNA rearrangements mostly happen in the region from Cox1 to Nad3, the same area where the duplicated genes are located. The rearrangements within Gryphaeidae could be explained by a "repeat-random loss model". Phylogenetic analyses revealed Gryphaeidae formed by H.sinensis + H.hyotis as sister to Ostreidae, whereas the phylogenetic relationship within the latter group remains unresolved. The present study indicated the mitogenomic diversity within Gryphaeidae and could also provide important data for future better understanding the gene order rearrangements within superfamily Ostreoidea.

Pea crab-oyster interspecific interaction on tropical coast: Brachyuran pinnotherid Zaops ostreum (Say, 1817) living in the host bivalve ostreid Crassostrea brasiliana (Lamarck, 1819)

In this study, we report the association between the pea crab Zaops ostreum (Say, 1817) living in the oyster Crassostrea brasiliana (Lamarck, 1819), collected in an estuarine region of Northeast Brazil. Oysters were collected along the mouth of the Santa Cruz Channel, Barra de Catuama (State of Pernambuco), between 2016 and 2017. A total of 224 oysters and 38 crabs were collected. Relative density of Z. ostreum was 16.96% (7.14% for males and 9.82% for females) in analyzed oysters. Prevalence during dry season ranged from 6.25% to 15.60%, whereas in rainy season ranged from 3.10% to 12.50%. Z. ostreum proportion of females to males was 1:0.73. Most occurrences were female-male couples (79.29%) with no isolated males or triple occupancy being observed. Female-male couples and ovigerous females were detected throughout most of the studied period, possibly indicating a distinct reproduction behaviour on tropical areas. This association expands knowledge on the aspects of social behaviour and host range of Z. ostreum, remarkably associated with bivalves of the Family Ostreidae.

The Complete Mitochondrial Genome of Hyotissa hyotis (Bivalvia: Gryphaeidae) Reveals a Unique Gene Order within Ostreoidea

The mitochondrial (mt) genome is an important tool when studying the evolution of metazoan animals. The oyster family Gryphaeidae, together with Ostreidae, is one of the two extant taxa of superfamily Ostreoidea. Up until now, the available mitochondrial genomes of oysters were all limited to family Ostreidae. In the present study, the first complete mtDNA of family Gryphaeidae represented by Hyotissa hyotis was sequenced and compared with other available ostreoid mtDNA. The mtDNA of H. hyotis is 22,185 bp in length, encoding 13 protein-coding-genes (PCGs), two ribosomal RNA (rRNA) and 23 transfer RNA (tRNA) genes. Within all the intergenic regions that range from 2 to 1528 bp, two large non-coding regions were identified. The first large non-coding region, located between Cox1 and trnA, contains 1528 nucleotides, while the second one is 1191 bp in length and positioned between Cytb and Nad2. The nucleotide composition of the whole mtDNA is A + T biased, accounting for 59.2%, with a negative AT skew value of −0.20 and a positive GC skew value of 0.33. In contrast to the mtDNA of Ostreidae, neither the split of rrnL nor rrnS was detected in that of H. hyotis. The duplication of trnW of H. hyotis was also discovered for the first time within Ostreoidea. The gene order of H. hyotis is quite different from those of ostreids, indicating extensive rearrangements within superfamily Ostreoidea. The reconstructed phylogeny supported H. hyotis as sister to Ostreidae, with the latter clade formed by Ostrea + (Saccostrea + Crassostrea). This study could provide important information for further understanding the mitochondrial evolution of oysters.

Reproductive Characteristics of the Flat Oyster Ostrea denselamellosa (Bivalvia, Ostreidae) Found on the Southern Coast of South Korea

In this study, we investigated the reproductive pattern of the commercially and ecologically important species, Ostrea denelamellosa, to inform stock management strategies in South Korea. Prior to the reproduction experiment, the complete mitochondrial (mt) genome of the flat oyster, Ostrea denselamellosa, was analyzed using next-generation sequencing technology. Then, to determine the reproductive pattern of Ostrea denselamellosa, we investigated monthly changes in the gametogenesis, reproductive cycle, and sex ratio from January to October 2021 in females. The total length of the mt genome sequence of O. denselamellosa was 16,225 bp and contained 37 genes (13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes). Molecular phylogenetic comparison with 20 known species of Pteriomorphia showed that O. denselamellosa belongs to the family Ostreidae. In addition, O. denselamellosa clustered together with the O. denselamellosa Chinese strain, with a bootstrap value of 100%. Histological analysis indicated a discrepancy in gamete development of O. denselamellosa with synchronous maturation of oocytes and asynchronous development of spermatozoa in gonads. The spawning activity occurred between May and September with a temperature range gap of 6.5 °C. The spawning activity occurred from May when the temperature reached 16.7 °C until September when the temperature dropped below 23.2 °C. Furthermore, sex ratio bias was observed. This is the first study to report the complete mt genome sequence and examine the reproductive pattern in native O. denselamellosa in South Korea. Overall, these findings will help enhance the knowledge for the management and sustainable fishery of endangered oyster species including O. denselamellosa in the South Sea of Korea.

Sperm Repository for a Breeding Program of the Eastern Oyster Crassostrea virginica: Sample Collection, Processing, Cryopreservation, and Data Management Plan.

Simple SummaryThe Eastern oyster Crassostrea virginica is one of the most important fishery and aquaculture species in the USA and is a keystone species for coastal reefs. A breeding program was initiated in 2019 to support the fast-growing aquaculture industry for this species in the Gulf of Mexico. Oysters from wild populations in embayment along the U.S. Gulf of Mexico coast were used as broodstock for the program to maximize genetic diversity. A sperm repository of the broodstock, including a total of 102 male oysters from the 17 collection sites, was established to support the breeding project. Sperm collection was accomplished by strip spawn, and fresh sperm production, motility, and fertility were recorded for quality analysis. Cryopreserved sperm samples were sorted, labelled, archived, and stored in liquid nitrogen for future use. Post-thaw motility and plasm membrane integrity were recorded as post-thaw quality parameters. Overall, this study demonstrated sperm sample collection, processing, cryopreservation, and a data management plan involved in the establishment of the sperm repository. The streamlined procedure can serve as a template for construction of oyster germplasm repositories for breeding programs.The Eastern oyster Crassostrea virginica (Family Ostreidae) is one of the most important fishery and aquaculture species in the U.S. and is a keystone species for coastal reefs. A breeding program was initiated in 2019 to support the fast-growing aquaculture industry culturing this species in the Gulf of Mexico. Oysters from 17 wild populations in embayment along the U.S. Gulf of Mexico coast from southwest Florida to the Matagorda Bay, Texas were used as broodstock for the program to maximize genetic diversity in the base population. A sperm repository of the broodstock was established to support the breeding project. The goal of this study was to demonstrate the sperm sample collection, processing, cryopreservation, and the data management plan involved in the establishment of a sperm germplasm repository of base populations. The supporting objectives were to: (1) develop a data management plan for the sperm repository; (2) streamline the procedure for sample collection, processing, and cryopreservation; (3) incorporate sperm quality analysis into the procedure, and (4) archive the cryopreserved samples as a repository for future use in the breeding program. This sperm repository included a total of 102 male oysters from the 17 collection sites (six oysters per site). A data management plan was developed with six categories, including sample collection, phenotype, fresh sperm, genotype, cryopreservation, and post-thaw sperm, as guide for data collection. Sperm collection was accomplished by strip spawn, and fresh sperm production, motility, and fertility were recorded for quality analysis. Cryopreserved sperm samples were sorted, labelled, archived, and stored in liquid nitrogen for future use. Post-thaw motility (1–30%) and plasm membrane integrity (15.34–70.36%) were recorded as post-thaw quality parameters. Overall, this study demonstrated a streamlined procedure of oyster sperm collection, processing, and cryopreservation for establishing a sperm repository that can serve as a template for construction of oyster germplasm repositories for breeding programs.

Morphological and Mitochondrial DNA Analyses of Oysters in the Northern Bay of Bengal, Bangladesh

The geographic boundaries of many important habitat-building shallow estuarine oyster (Family Ostreidae) species are poorly understood, especially in subtropical and tropical waters. These keystone species often have extensive historical and extant ranges, in part because of their ability to adapt to diverse environmental conditions and the transfer and introduction of a few species worldwide for aquaculture production. In addition, oysters exhibit morphological plasticity additionally confounding species identification and taxonomy. Molecular techniques have led to significant improvements in oyster systematics and taxonomy but have not been applied to oysters from many tropical regions, including the coastal areas of the Indian Ocean such as Bangladesh. Because species' identification based on morphological traits alone, in this case primarily shell characteristics, were inadequate, phylogenetic analyses of mitochondrial cytochrome oxidase subunit I gene fragments was also done to confirm the identity of oyster specimens collected from Bangladesh coastal waters. Phylogenetic analyses of collected oyster samples confirmed the two monophyletic subclades of the Ostreidae family Crassostrea and Saccostrea, and five oyster lineages from the region of Bangladesh were identified: Crassostrea gryphoides, Crassostrea belcheri, Saccostrea cuccullata lineage B, S. cuccullata lineage F, and Saccostrea mordax. A new addition to the list of Crassostrea species, C. belcheri was found in Bangladesh, but C. belcheri, C. gryphoides, and S. cuccullata are considered “common” species in the neighboring states of India and Myanmar indicating a widespread distribution of these species along the entire coast of the Bay of Bengal. However, S. mordax, is a new record for the Bay of Bengal region including the coastal waters of Andaman and Nicobar Islands, and thus extends the geographical distribution of this species.

The genome of the oyster Saccostrea offers insight into the environmental resilience of bivalves.

Oysters are keystone species in estuarine ecosystems and are of substantial economic value to fisheries and aquaculture worldwide. Contending with disease and environmental stress are considerable challenges to oyster culture. Here we report a draft genome of the Sydney Rock Oyster, Saccostrea glomerata, an iconic and commercially important species of edible oyster in Australia known for its enhanced resilience to harsh environmental conditions. This is the second reference genome to be reported from the family Ostreidae enabling a genus-level study of lophotrochozoan genome evolution. Our analysis of the 784-megabase S. glomerata genome shows extensive expansions of gene families associated with immunological non-self-recognition. Transcriptomic analysis revealed highly tissue-specific patterns of expression among these genes, suggesting a complex assortment of immune receptors provide this oyster with a unique capacity to recognize invading microbes. Several gene families involved in stress response are notably expanded in Saccostrea compared with other oysters, and likely key to this species’ adaptations for improved survival higher in the intertidal zone. The Sydney Rock Oyster genome provides a valuable resource for future research in molluscan biology, evolution and environmental resilience. Its close relatedness to Crassostrea will further comparative studies, advancing the means for improved oyster agriculture and conservation.

Microbial Ecology of the Bivalvia, with an Emphasis on the Family Ostreidae

Rapid improvements in the technology used to assess microbial communities have led to an expansion of the breadth and scope of microbial ecology research over the past 20 y. The rapid increase in microbiome research, spurred by nextgeneration amplicon sequencing, has allowed researchers to characterize the microbial communities of organisms and environments which were previously poorly understood. Research on marine invertebrates is still developing, with the mechanisms that determine interactions between the host and their associated microbes largely unknown. Bivalves are of particular interest because of their crucial ecological and economic roles. With the anticipation of shifting environmental conditions, defining the natural variation and role of bivalve-associated microbes is vital to more complex research questions. The current knowledge of the spatial and temporal distributions of bivalve-associated microbes, microbial functional and genetic diversity, host-specific and tissue-specific interactions, and core microbial community composition is summarized here, as well as the beginning stages of understanding the role of microbiome in bivalve physiology and disease susceptibility.

Morphogenetic and population structure of two species marine bivalve (Ostreidae: Saccostrea cucullata and Crassostrea iredalei) in Aceh, Indonesia

Ramadhaniaty M, Setyobudiandi I, Madduppa HH. 2018. Morphogenetic and population structure of two species marine bivalve (Ostreidae: Saccostrea cucullata and Crassostrea iredalei) in Aceh, Indonesia. Biodiversitas 19: 978-988. Oysters (Family Ostreidae) are mollusks, with high levels of phenotypic plasticity and wide geographic distribution. Oysters are a challenging group for morphological identification and genetic populations study. Saccostrea cucullata and Crassostrea iredalei are oysters from bivalve class that lives in the intertidal area and mangrove ecosystem. To clarify the morphology, genetic diversity and population structure of the two forms of S. cucullata and C. iredalei, we collected and studied oysters from three locations along the coastal region of Aceh by using morphometric method and 16 S mtDNA sequences analysis. We also added more oysters sequences from China, Japan, and Thailand to determine the connectivity between all populations. Morphometric characteristics of the oyster showed a negative allometric growth pattern, which means the rate of length gain is faster than that of the weight gain. The genetic distance from S. cucullata was 0.003-0.004 (Fst = 0.708) and C. iredalei was 0.000 (Fst = 0.971). The long genetic distance and high fixation index (Fst) in the oysters population are caused by the close geographical distance of the species in the three populations. The haplotype diversity value from S. cucullata and C. iredalei were 20 and 3, respectively. The haplotype showed the connectivity among the oyster populations which indicated by the gene flow pattern. The gene flow was affected by geographical distance and environmental complexity.

Molecular detection of parasites (Trematoda, Digenea: Bucephalidae and Monorchiidae) in the European flat oyster Ostrea edulis (Mollusca: Bivalvia)

Members of the globally distributed bivalve family Ostreidae (oysters) have a significant role in marine ecosystems and include species of high economic importance. In this work, we report the occurrence of digenean parasites of the families Bucephalidae (Prosorhynchoides sp.) and Monorchiidae (Postmonorchis sp.) in Mediterranean native populations of Ostrea edulis (but not in the introduced Magallana gigas). Molecular detection was based on DNA sequencing of the ribosomal intergenic spacer 2 (ITS2) marker. The importance of detecting the presence of overlooked digenean parasites in Mediterranean oysters is discussed.

Finding of the pea crab Pinnaxodes mutuensis Sakai, 1939 (Crustacea: Decapoda: Pinnotheridae) in an unusual host in Busse Lagoon, southern Sakhalin

The symbiotic crab Pinnaxodes mutuensis Sakai, 1939 was found in the mantle cavity of the mud-burrowing bivalve Mya arenaria Linnaeus, 1758 (the family Myidae) in Busse Lagoon at southern Sakhalin Island. Along the Russian coasts, this species has been previously found in the mantle cavity of epifaunal bivalves of the family Mytilidae [Modiolus difficilis (Deshayes in Maillard, 1863), Modiolus modiolus (Linnaeus, 1758), Mytilus edulis Linnaeus, 1758, Crenomytilus grayanus (Dunker, 1853)] and the family Ostreidae [Crassostrea gigas (Thunberg, 1793)]. New data on the morphology and ecology of this crab are presented.

Molecular phylogenetics and systematics of the bivalve family Ostreidae based on rRNA sequence-structure models and multilocus species tree.

The bivalve family Ostreidae has a worldwide distribution and includes species of high economic importance. Phylogenetics and systematic of oysters based on morphology have proved difficult because of their high phenotypic plasticity. In this study we explore the phylogenetic information of the DNA sequence and secondary structure of the nuclear, fast-evolving, ITS2 rRNA and the mitochondrial 16S rRNA genes from the Ostreidae and we implemented a multi-locus framework based on four loci for oyster phylogenetics and systematics. Sequence-structure rRNA models aid sequence alignment and improved accuracy and nodal support of phylogenetic trees. In agreement with previous molecular studies, our phylogenetic results indicate that none of the currently recognized subfamilies, Crassostreinae, Ostreinae, and Lophinae, is monophyletic. Single gene trees based on Maximum likelihood (ML) and Bayesian (BA) methods and on sequence-structure ML were congruent with multilocus trees based on a concatenated (ML and BA) and coalescent based (BA) approaches and consistently supported three main clades: (i) Crassostrea, (ii) Saccostrea, and (iii) an Ostreinae-Lophinae lineage. Therefore, the subfamily Crassotreinae (including Crassostrea), Saccostreinae subfam. nov. (including Saccostrea and tentatively Striostrea) and Ostreinae (including Ostreinae and Lophinae taxa) are recognized. Based on phylogenetic and biogeographical evidence the Asian species of Crassostrea from the Pacific Ocean are assigned to Magallana gen. nov., whereas an integrative taxonomic revision is required for the genera Ostrea and Dendostrea. This study pointed out the suitability of the ITS2 marker for DNA barcoding of oyster and the relevance of using sequence-structure rRNA models and features of the ITS2 folding in molecular phylogenetics and taxonomy. The multilocus approach allowed inferring a robust phylogeny of Ostreidae providing a broad molecular perspective on their systematics.

Spermiogenesis and Taxonomical Values of Sperm Ultrastructures in Male Crassostrea ariakensis (Fujita & Wakiya, 1929) (Pteroirmorphia: Ostreidae) in the Estuary of the Seomjin River, Korea.

Characteristics of the developmental stages of spermatids during spermiogenesis and phylogenetic classicfication of the species using sperm ultrastructures in male Crassostrea ariakensis were investigated by transmission electron microscope observations. The morphology of the spermatozoon of this species has a primitive type and is similar to those of Ostreidae. Ultrastructures of mature sperms are composed of broad, modified cap-shaped acrosomal vesicle and an axial rod in subacrosomal materials on an oval nucleus, four spherical mitochondria in the sperm midpiece, and satellite fibres which appear near the distal centriole. The axoneme of the sperm tail shows a 9+2 structure. Accordingly, the ultrastructural characteristics of mature sperm of C. ariakensis resemble to those of other investigated ostreids in Ostreidae in the subclass Pteriomorphia. In this study, particularly, two transverse bands (stripes) appear at the anterior region of the acrosomal vesicle of this species, unlike two or three transverse bands (stripes) in C. gigas. It is assumed that differences in this acrosomal substructure are associated with the inability of fertilization between the genus Crassostrea and other genus species in Ostreidae. Therefore, we can use sperm ultrastructures and morphologies in the resolution of taxonomic relationships within the Ostreidae in the subclass Pteriomorphia. These spermatozoa, which contain several ultrastructures such as acrosomal vesicle, an axial rod in the sperm head part and four mitochondria and satellite fibres in the sperm midpiece, belong to the family Ostreidae in the subclass Pteriomorphia.

Identifying the true oysters (Bivalvia: Ostreidae) with mitochondrial phylogeny and distance‐based DNA barcoding

Oysters (family Ostreidae), with high levels of phenotypic plasticity and wide geographic distribution, are a challenging group for taxonomists and phylogenetics. As a useful tool for molecular species identification, DNA barcoding might offer significant potential for oyster identification and taxonomy. This study used two mitochondrial fragments, cytochrome c oxidase I (COI) and the large ribosomal subunit (16S rDNA), to assess whether oyster species could be identified by phylogeny and distance-based DNA barcoding techniques. Relationships among species were estimated by the phylogenetic analyses of both genes, and then pairwise inter- and intraspecific genetic divergences were assessed. Species forming well-differentiated clades in the molecular phylogenies were identical for both genes even when the closely related species were included. Intraspecific variability of 16S rDNA overlapped with interspecific divergence. However, average intra- and interspecific genetic divergences for COI were 0-1.4% (maximum 2.2%) and 2.6-32.2% (minimum 2.2%), respectively, indicating the existence of a barcoding gap. These results confirm the efficacy of species identification in oysters via DNA barcodes and phylogenetic analysis.

Specific Detection of Pacific Oyster (Crassostrea gigas) Larvae in Plankton Samples Using Nested Polymerase Chain Reaction

Management of sustainable Pacific oyster fisheries would be assisted by an early, rapid, and accurate means of detecting their planktonic larvae. Reported here is an approach, based on polymerase chain reaction (PCR), for the detection of Pacific oyster larvae in plankton samples. Species-specific primers were designed by comparing partial mitochondrial cytochrome oxidase subunit I (COI) sequences from Crassostrea gigas, with other members of the family Ostreidae including those of Crassostrea angulata. Assay specificity was empirically validated through screening DNA samples obtained from several species of oysters. The assay was specific as only C. gigas samples returned PCR-positive results. A nested PCR approach could consistently detect 5 or more D-hinge-stage larvae spiked into a background of about 146 mg of plankton. The assay does not require prior sorting of larvae. We conclude that the assay could be used to screen environmental and ballast water samples, although further specificity testing against local bivalve species is recommended in new locations.

Restriction enzyme digestion chromosome banding in Crassostrea and Ostrea species: comparative karyological analysis within Ostreidae

Reliable banding techniques are a major necessity for genetic research in oysters. In this study, we carried out the cytogenetic characterization of four oyster species (family Ostreidae) using restriction endonuclease treatments. Chromosomes were treated with three different restriction enzymes, stained with Giemsa, and examined for banding patterns. The following species were studied: Crassostrea gigas (2n = 20; total number of bands with ApaI, 74; HaeIII, 61; PstI, 76), Crassostrea angulata (2n = 20; ApaI, 62; HaeIII, 61; PstI, 55) (subfamily Crassostreinae), Ostrea edulis (2n = 20; ApaI, 82; HaeIII, 59; PstI, 66), and Ostrea conchaphila (2n = 20; ApaI, 68; HaeIII, 62; PstI, 69) (subfamily Ostreinae). Treatment of samples with ApaI, HaeIII, and PstI produced specific banding patterns, which demonstrates the potential of these enzymes for chromosome banding in oysters. This is of special interest, since it has been recently shown in mammalian chromosomes that restriction enzyme banding is compatible with fluorescence in situ hybridization. This study therefore provides a fundamental step in genome mapping of oysters, since chromosome banding with restriction enzymes facilitates physical gene mapping in these important aquaculture species. The analysis of the banded karyotypes revealed a greater similarity within the genera of Crassostrea and Ostrea than between them.

The Middle Cenomanian oldest Agerostrea (Bivalvia; Ostreidae) and its reconstructed mode of life

The Middle Cenomanian oldest Agerostrea (Bivalvia; Ostreidae) and its reconstructed mode of life

A cytogenetic method to obtain chromosomes for studies of banding and fine morphology of karyotypes in bivalve mollusks of the family Ostreidae

The studies of banding patterns of chromosomes in bivalve mollusks of the family Ostreidae have not been developed satisfactorily due to the lack of a suitable method that enables the obtention of chromosomes in a proper condition. The production of chromosomal fields in cold by means of a modification to the dripping and air drying method from embryos and larvae obtained from in vitro fertilization, and the control of the spiralization degree of the chromosomes, are achieved by the application of colchicine pulses for periods of 30, 45 and 60 minutes. These chromosomes show a certain degree of synchronisation due to the use of oyster early embryos and larvae in which the cell division is very frequent. Separation of cells in division was achieved with a 50% acetic acid solution, at 37ºC. Chromosomes obtained in this manner can be stained successfully for the severa1 different bands willing to be studied.