Marine Invertebrate Cell Cultures: New Millennium Trends

This review analyzes activities in the field of marine invertebrate cell culture during the years 1999 to 2004 and compares the outcomes with those of the preceding decade (1988 to 1998). During the last 5 years, 90 reports of primary cell culture studies of marine organisms belonging to only 6 taxa (Porifera, Cnidaria, Crustacea, Mollusca, Echinodermata, and Urochordata) have been published. This figure represents a 2-fold increase in the annual number of publications over the decade 1988 to 1998. Three other trends distinguish the two reviewed periods. First, in recent years studies attempting to improve cell culture methodologies have decreased, while interest in applications of already existing methodologies has increased. This reflects the effects of short-term cultures in attracting new researchers and scientific disciplines to the field. Second, only 17.8% of the recent publications used long-term cultures, compared with 30.0% of the publications in the previous decade. Third, during recent years research in cell cultures has studied fewer model species more extensively (mainly, Botryllus schlosseri, Crassostrea, Mytilus, Penaeus, and Suberites domuncula), signifying a shift from previous investigations that had studied a more diverse range of organisms. From 1988 to 1998 the phylum Mollusca was the most studied taxon (34.4%), but recent years have seen more studies of Porifera and Crustacea (30.0% and 32.2% of publications) than of Mollusca (21.1%). Still, not even a single established cell line from any marine invertebrate has yet been made available. However, the use of new cellular, genomic, and proteomic tools may fundamentally change our strategy for the development of cell cultures from marine invertebrates.     

Stem cells of marine invertebrates: Regulation of proliferation and induction of differentiation in vitro

The review surveys own and the literature data on the plasticity of marine invertebrate stem cells. Stem and embryonic cell cultures of marine invertebrates are a novel model system characterized by a high level of physiological and synthetic processes. The production of biologically active substances in vitro may be an alternative to chemical synthesis and aquaculture. The factors involved in determination and maintenance of the pluripotency of marine invertebrate stem cells have been analyzed. The technology of the directed differentiation of marine invertebrate stem cells into certain functionally active cells in vitro embraces the use of different growth factors, various natural and artificial substrates, and unique bioactive compounds from marine invertebrate tissues. To increase the expression levels of regulatory genes, we applied genetically engineered constructions with foreign genes. The regulation of growth and differentiation of marine invertebrate stem cells opens new prospective uses for their application in marine biotechnology and is helpful for research in developmental biology.     

Cell Cultures from Marine Invertebrates: New Insights for Capturing Endless Stemness

Despite several decades of extensive research efforts, there is yet no single permanent cell line available from marine invertebrates as these cells stop dividing in vitro within 24–72 h after their isolation, starting cellular quiescence. This ubiquitous quiescent state should be modified in a way that at least some of the quiescent cells will become pluripotent, so they will have the ability to divide and become immortal. Following the above need, this essay introduces the rationale that the discipline of marine invertebrates’ cell culture should gain from applying of two research routes, relevant to mammalian systems but less explored in the marine arena. The first is the use of adult stem cells (ASC) from marine organisms. Many marine invertebrate taxa maintain large pools of ASC in adulthood. Ample evidence attests that these cells from sponges, cnidarians, flatworms, crustaceans, mollusks, echinoderms, and ascidians play important roles in maintenance, regeneration, and asexual cloning, actively proliferating in vivo, resembling the vertebrates’ cancer stem cells features. The second route is to target resting somatic cell constituents, manipulating them in the same way as has recently been performed on mammalian induced pluripotent stem (iPS) cells. While “iPS cells” are the outcome of an experimental manipulation, ASC are natural and rather frequent in a number of marine invertebrates. Above two cell categories reveal that there are more than a few types of seeds (cells) waiting to be sowed in the right soil (in vitro environmental conditions) for acquiring stemness and immortality. This rationale carries the potential to revolutionize the discipline of marine invertebrate cell cultures. When cultured “correctly,” ASC and “iPS cells” from marine invertebrates may stay in their primitive stage and proliferate without differentiating into cells lineages, harnessing the stem cell’s inherent abilities of self-replication versus differentiated progenies, toward the development of immortal cell lines.     

Metagenomic analysis of the marine coastal invertebrates of South Korea as assessed by Ilumina MiSeq

Metagenomic analysis was carried out for the first time on the marine coastal invertebrates of South Korea. Samples collected from coastal areas of Korea were filtered through a 63 µm mesh, then their 18S rDNA V4 regions were amplified. High-throughput sequencing of PCR amplicons using Illumina MiSeq and BLAST against the SILVA database showed that a total of 319 eukaryotic Operational Taxonomic Units were identified at the species level. Annelida, Arthropoda, Mollusca, Nematoda, and Platyhelminthes and for 92.23% of the total 103 metazoan species belonging to 101 genera, 75 families, and 10 phyla. Of these, several taxa previously unreported to exist in Korea were detected at the family level compared with the integrated database from three main Korean biodiversity DBs (MABIK, KOMBIS, and MRBR). Analysis of beta diversity of the community structure of invertebrates indicated that the composition of marine invertebrates is likely to be affected by habitat type rather than geographical distance. The present study showed that metagenomic high-throughput technology can be used to unravel species diversity and for various studies regarding marine invertebrate community structure.     

EGFP基因在中国明对虾原代培养细胞中的导入和表达

本文以我国重要水产养殖动物中国明对虾（Fenneropenaeus chinensis）贴壁培养和悬浮培养的血细胞、植块培养的类淋巴器官（Oka器官）细胞和卵巢细胞为材料,通过磷酸钙共沉淀法、脂质体介导的转染（脂染）和电穿孔法等多种方法进行了导入EGFP基因的实验。结果表明,通过脂染可以成功地将质粒DNA导入悬浮培养的血细胞、植块培养的Oka器官细胞和卵巢细胞,并使报告基因EGFP得到表达。     

Investigating the establishment of primary cultures of hemocytes from <Emphasis Type="Italic">Mytilus edulis</Emphasis>

Anthropogenic influences on the environment have been become a focal point for many social and political endeavors. With an ever-increasing rate of new contaminants being introduced into the environment every year, regulatory policies have begun to shift to prevention rather than mitigation. However, current in vivo testing strategies, in addition to ethical considerations, are too expensive and time consuming to adequately screen potential contaminants within a realistic timeframe. As a result, in vitro testing on cell cultures has been identified as an ideal alternative testing strategy for emerging contaminants. In the context of ecotoxicology, in vitro testing has had limited use particularly with marine invertebrates like the marine mussel Mytilus edulis mainly due to difficulties in establishing longer term cell cultures and cell lines. The aim of this study was to define an optimal technique (extraction and maintenance) for establishing a primary cell culture on M. edulis hemocytes that could be used for screening contaminants.     

Isolation and diversity of planctomycetes from the sponge Niphates sp., seawater, and sediment of Moreton Bay, Australia

Planctomycetes are ubiquitous in marine environment and were reported to occur in association with multicellular eukaryotic organisms such as marine macroalgae and invertebrates. Here, we investigate planctomycetes associated with the marine sponge Niphates sp. from the sub-tropical Australian coast by assessing their diversity using culture-dependent and -independent approaches based on the 16S rRNA gene. The culture-dependent approach resulted in the isolation of a large collection of diverse planctomycetes including some novel lineages of Planctomycetes from the sponge as well as sediment and seawater of Moreton Bay where this sponge occurs. The characterization of these novel planctomycetes revealed that cells of one unique strain do not possess condensed nucleoids, a phenotype distinct from other planctomycetes. In addition, a culture-independent clone library approach identified unique planctomycete 16S rRNA gene sequences closely related to other sponge-derived sequences. The analysis of tissue of the sponge Niphates sp. showed that the mesohyl of the sponge is almost devoid of microbial cells, indicating this species is in the group of ‘low microbial abundant’ (LMA) sponges. The unique planctomycete 16S rRNA gene sequences identified in this study were phylogenetically closely related to sequences from LMA sponges in other published studies. This study has revealed new insights into the diversity of planctomycetes in the marine environment and the association of planctomycetes with marine sponges.     

Barcoding Antarctic Biodiversity: current status and the CAML initiative,a case study of marine invertebrates

The Census of Antarctic Marine Life (CAML) aims to collate DNA barcode data for Antarctic marine species. DNA barcoding is a technique that uses a short gene sequence from a standardised region of the genome as a diagnostic ‘biomarker’ for species. This study aimed to quantify genetic data currently available in GenBank in order to establish whether a representative cross-section of Antarctic marine taxa and bio-geographic areas has been sequenced and to propose priorities for barcoding, with a particular emphasis on marine invertebrate species. It was found that, amongst marine invertebrate fauna, sequence information covers a limited range of taxa and areas—mainly Crustacea, Annelida and Mollusca from the Weddell Sea and the Antarctic Peninsula. Only 15% of genes sequenced in Antarctic marine invertebrates were the standard barcode gene cytochrome c oxidase subunit 1 (CO1), the majority were other nuclear and mitochondrial genes. There is an urgent need for more in-depth genetic barcoding and species identification studies in Antarctic science, from a range of taxa and areas, given the rate of climate-driven habitat changes that might lead to extinctions in the region. CAML hopes to redress the balance, by collecting and sequencing over the circum-Antarctic area, using material from voyages that occurred during 2008 and 2009, within the framework of the International Polar Year (IPY).     

Normal giants? Temporal and latitudinal shifts of Palaeozoic marine invertebrate gigantism and global change

During and after the Cambrian explosion, very large marine invertebrate species have evolved in several groups. Gigantism in Carboniferous land invertebrates has been explained by a peak in atmospheric oxygen concentrations, but Palaeozoic marine invertebrate gigantism has not been studied empirically and explained comprehensively. By quantifying the spatiotemporal distribution of the largest representatives of some of the major marine invertebrate clades (orthoconic cephalopods, ammonoids, trilobites, marine eurypterids), we assessed possible links between environmental parameters (atmospheric or oceanic oxygen concentrations, ocean water temperature or sea level) and maximum body size, but we could not find a straightforward relationship between both. Nevertheless, marine invertebrate gigantism within these groups was temporally concentrated within intervals of high taxonomic diversity (Ordovician, Devonian) and spatially correlated with latitudes of high occurrence frequency. Regardless of whether temporal and spatial variation in sampled diversity and occurrence frequency reflect true biological patterns or sampling controls, we find no evidence that the occurrences of giants in these groups were controlled by optimal conditions other than those that controlled the group as a whole; if these conditions shift latitudinally, occurrences of giants will shift as well. It is tempting to attribute these shifts to contemporary changes in temperature, oxygen concentrations in the atmosphere and the oceans as well as global palaeogeography over time, but further collection‐based studies are necessary on finer stratigraphic and phylogenetic resolution to corroborate such hypotheses and rule out sampling or collection biases.     

鱼类的胚胎干细胞

胚胎干细胞(ES)是未分化的细胞培养物，来自动物的早期胚胎。它们能成为稳定的细胞系和长期冻存。在适当的条件下，ES细胞能分化成各种细胞类型，包括生殖细胞。这样，ES细胞就提供了一个有效的纽带，将动物基因组的体外和体内遗传操作连系起来。ES细胞的魅力就由其在产生和分析基因敲除老鼠中显现出来。目前，ES细胞技术仅见之老鼠，因其它脊椎动物的ES细胞的培养和建系难获成功。在鱼类，人们已做了大量的尝试。我们以青鳉(Oryzias latipes)作为建立鱼类ES细胞技术的模式，通过建立并应用无滋养层细胞的培养条件，获得了来自中期囊胚的ES细胞系。青鳉的ES细胞和老鼠的ES细胞有很多共同特征，如二倍体核型、分化潜力和形成嵌合体。因此，在鱼类建立和应用ES细胞技术是可能的。青鳉ES细胞的培养条件已成功地应用到其它鱼类如斑马鱼甚至海水鱼。本文旨在以青鳉为模式，综述获得和应用模式鱼和经济鱼ES细胞的主要进展和前景。     

Microbial antagonism: a neglected avenue of natural products research

Competition amongst microbes for space and nutrients in the marine environment is a powerful selective force which has led to the evolution of a variety of effective strategies for colonising and growing on surfaces. We are particularly interested in the chemical ecology of marine epibiotic bacteria which live on the surfaces of marine algae or invertebrates. Over 400 strains of surface-associated bacteria from various species of seaweed and invertebrate from Scottish coastal waters were isolated and 35% of them shown to produce antimicrobial compounds. This is a much higher proportion than free living marine isolates or soil bacteria. In addition, many strains which did not normally produce antibiotics could be induced to do so by exposing them to small amounts of live cells, supernatants from other bacterial cultures or other chemicals. Thus the number of strains able to produce antibiotics appears to be much higher than previously thought. Induction of antibiotic production was elicited by other marine epibionts and also by terrestrial human pathogens such as Bacillus subtilis, Escherichia coli and Pseudomonas aeruginosa. An understanding of this type of chemical induction and the factors regulating non-constitutive secretion of antimicrobial compounds will allow more effective strategies for searching for new chemotherapeutic antibiotics to be designed.     

The presence,nature, and role of gut microflora in aquatic invertebrates: A synthesis

This review of the literature concerns the gut microbiota of aquatic invertebrates and highlights the questions and processes that merit attention if an understanding of the role of gut microbes in the physiology of host invertebrates and nutrient dynamics of aquatic systems is to be gained. A substantial number of studies report the presence of gut microbes in aquatic invertebrates. Crustacea, Mollusca, and Echinodermata have received the most attention, with few studies involving other invertebrate groups. Different types of associations (e.g., ingestion, contribution of exoenzymes, incubation, parasitism) are reported to occur between gut microbes and aquatic invertebrates, and it is clear that gut bacterial communities cannot be treated as single functional entities, but that individual populations require examination. In addition, gut microbes may be either ingested transients or residents, the presence of which have different implications for the invertebrate. The most commonly reported genera of gut bacteria are Vibrio, Pseudomonas, Flavobacterium, Micrococcus, and Aeromonas. Quite a number of authors report the physiological properties of gut microbes (including enzyme activities and attributes such as nitrogen fixation), while less attention has been given to consideration of the colonization sites within the digestive tract, the density and turnover of gut bacteria, and the factors affecting the presence and nature of gut microflora. In addition, although a few studies have demonstrated a positive relationship between invertebrates and their gut microbiota, particularly with regard to nutrient gain by the invertebrate, very little conclusive evidence exists as to the role of bacteria in the physiology of host invertebrates. This has resulted from a lack of process-oriented studies. The findings for aquatic gut microbes are compared to those of gut bacteria associated with terrestrial invertebrates, where gut microbes contribute significantly to nutrient gain by the host in some environments.     

Allorecognition and chimerism in an invertebrate model organism

The presence of highly specific histocompatibility reactions in colonial marine invertebrates that lack adaptive immune systems (such as the sponges, cnidarians, bryozoans and ascidians) provides a unique opportunity to investigate the evolutionary roots of allorecognition and to explore whether homologous innate recognition systems exist in vertebrates. Conspecific interactions among adult animals in these groups are regulated by highly specific allorecognition systems that restrict somatic fusion to self or close kin. In Hydractinia (Cnidaria:Hydrozoa), fusion/rejection responses are controlled by two linked genetic loci. Alleles at each locus are co-dominantly inherited. Colonies fuse if they share at least one haplotype, reject if they share no haplotypes, and display transitory fusion if they share only one allele in a haplotype—a pattern that echoes natural killer cell responses in mice and humans. Allorecognition in Hydractinia and other marine invertebrates serves as a safeguard against stem cell or germline parasitism thus, limiting chimerism to closely related individuals. These animals fail to become tolerant even if exposed during early development to cells from a histoincompatible individual. Detailed analysis of the structure and function of molecules responsible for allorecognition in basal marine invertebrates could provide clues to the innate mechanisms by which higher animals respond to organ and cell allografts, including embryonic tissues.Key words: allorecognition, chimerism, invertebrate, innate immune system     

Enhancing the diversity of breeding invertebrates within field margins of intensively managed grassland: Effects of alternative management practices

Severe declines in biodiversity have been well documented for many taxonomic groups due to intensification of agricultural practices. Establishment and appropriate management of arable field margins can improve the diversity and abundance of invertebrate groups; however, there is much less research on field margins within grassland systems. Three grassland field margin treatments (fencing off the existing vegetation “fenced”; fencing with rotavation and natural regeneration “rotavated” and; fencing with rotavation and seeding “seeded”) were compared to a grazed control in the adjacent intensively managed pasture. Invertebrates were sampled using emergence traps to investigate species breeding and overwintering within the margins. Using a manipulation experiment, we tested whether the removal of grazing pressure and nutrient inputs would increase the abundance and richness of breeding invertebrates within grassland field margins. We also tested whether field margin establishment treatments, with their different vegetation communities, would change the abundance and richness of breeding invertebrates in the field margins. Exclusion of grazing and nutrient inputs led to increased abundance and richness in nearly all invertebrate groups that we sampled. However, there were more complex effects of field margin establishment treatment on the abundance and richness of invertebrate taxa. Each of the three establishment treatments supported a distinct invertebrate community. The removal of grazing from grassland field margins provided a greater range of overwintering/breeding habitat for invertebrates. We demonstrate the capacity of field margin establishment to increase the abundance and richness in nearly all invertebrate groups in study plots that were located on previously more depauperate areas of intensively managed grassland. These results from grassland field margins provide evidence to support practical actions that can inform Greening (Pillar 1) and agri‐environment measures (Pillar 2) of the Common Agricultural Policy (CAP). Before implementing specific management regimes, the conservation aims of agri‐environment measures should be clarified by defining the target species or taxonomic groups.     

Conservation of Southern Ocean Islands: invertebrates as exemplars

The Southern Ocean Islands (SOI) have an exceptionally high conservation status, and human activity on the islands is low by comparison with more tropical islands. In consequence, overexploitation, pollution and habitat destruction have had little influence on the invertebrate biotas of the islands, although overexploitation of pelagic species has the potential for an indirect influence via reduction of nutrient inputs to the terrestrial systems. By contrast, invasive alien species, the local effects of global climate change, and interactions between them are having large impacts on invertebrate populations and, as a consequence, on ecosystem functioning. Climate change is not only having direct impacts on indigenous invertebrates, but also seems to be promoting the ease of establishment of new alien invertebrate species. It is also contributing to population increases of invertebrate alien species already on the islands, sometimes with pronounced negative consequences for indigenous species and ecosystem functioning. Moreover, alien plants and mammals are also affecting indigenous invertebrate populations, often with climate change expected to exacerbate the impacts. Although the conservation requirements are reasonably well-understood for terrestrial systems, knowledge of freshwater and marine near-shore systems is inadequate. Nonetheless, what is known for terrestrial, freshwater and marine systems suggests that ongoing conservation of SOI invertebrates requires intervention from the highest political levels internationally, to slow climate change, to local improvements of quarantine measures to reduce the rates and impacts of biological invasions.     

Immunological function in marine invertebrates: Responses to environmental perturbation

The inception of ecological immunology has led to an increase in the number of studies investigating the impact of environmental stressors on host immune defence mechanisms. This in turn has led to an increased understanding of the importance of invertebrate groups for immunological research. This review discusses the advances made within marine invertebrate ecological immunology over the past decade. By demonstrating the environmental stressors tested, the immune parameters typically investigated, and the species that have received the greatest level of investigation, this review provides a critical assessment of the field of marine invertebrate ecological immunology. In highlighting the methodologies employed within this field, our current inability to understand the true ecological significance of any immune dysfunction caused by environmental stressors is outlined. Additionally, a number of examples are provided in which studies successfully demonstrate a measure of immunocompetence through alterations in disease resistance and organism survival to a realized pathogenic threat. Consequently, this review highlights the potential to advance our current understanding of the ecological and evolutionary significance of environmental stressor related immune dysfunction. Furthermore, the potential for the advancement of our understanding of the immune system of marine invertebrates, through the incorporation of newly emerging and novel molecular techniques, is emphasized.     

Spineless and overlooked: DNA metabarcoding of autonomous reef monitoring structures reveals intra- and interspecific genetic diversity in Mediterranean invertebrates

The ability to gather genetic information using DNA metabarcoding of bulk samples obtained directly from the environment is crucial to determine biodiversity baselines and understand population dynamics in the marine realm. While DNA metabarcoding is effective in evaluating biodiversity at community level, genetic patterns within species are often concealed in metabarcoding studies and overlooked for marine invertebrates. In the present study, we implement recently developed bioinformatics tools to investigate intraspecific genetic variability for invertebrate taxa in the Mediterranean Sea. Using metabarcoding samples from Autonomous Reef Monitoring Structures (ARMS) deployed in three locations, we present haplotypes and diversity estimates for 145 unique species. While overall genetic diversity was low, we identified several species with high diversity records and potential cryptic lineages. Further, we emphasize the spatial scale of genetic variability, which was observed from locations to individual sampling units (ARMS). We carried out a population genetic analysis of several important yet understudied species, which highlights the current knowledge gap concerning intraspecific genetic patterns for the target taxa in the Mediterranean basin. Our approach considerably enhances biodiversity monitoring of charismatic and understudied Mediterranean species, which can be incorporated into ARMS surveys.     

A new look at evolution in the Galápagos: evidence from the late Cenozoic marine molluscan fauna

Endemism is not as common in the marine invertebrate fauna of the Galápagos Islands region as in the adjacent terrestrial biota. Marine invertebrates in the Galápagos are largely cosmopolitan species from the Panamic, Indo-Pacific, Californian, or Peruvian faunal provinces. However, an endemic component is also present in the fauna. The observed pattern among marine invertebrate organisms can be accounted for by at least two processes: (1) genetic continuity between mainland and island populations mediated through planktonic larvae; and (2) lower rates of intrinsic evolutionary change. The evolutionary scenario standardly applied to terrestrial organisms in the Galápagos, namely, adaptive radiation and speciation in reproductive isolation from mainland source populations, does not apply to all marine invertebrates. Evidence in support of the alternative scenario for marine invertebrates comes from both published records of species occurring in the islands and recent studies of fossil-bearing deposits on several islands in the archipelago. Two misconceptions–considering the islands and sedimentary deposits to be older than now thought, and equating the rate of evolution of the terrestrial biota with the marine biota–can lead to an incorrect interpretation of evolution in the Galápagos Contrasts between marine invertebrate and terrestrial organisms serve to illustrate some fundamental differences which have important evolutionary implications. Some of these are: endemism; dispersal; taxonomic relationships; island definitions; rates of evolutionary change; and age of fossils. In terms of Darwin's evolutionary scenario, terrestrial organisms represent the paradigm and marine organisms represent the paradox.     

Marine invertebrate cytochrome P450: emerging insights from vertebrate and insects analogies

Cytochrome P450 enzymes (P450s) are responsible for the oxidative metabolism of a plethora of endogenous and exogenous substrates. P450s and associated activities have been demonstrated in numerous marine invertebrates belonging to the phyla Cnidaria, Annelida (Polychaeta), Mollusca, Arthropoda (Crustacea) and Echinodermata. P450s of marine invertebrates and vertebrates show considerable sequence divergence and the few orthologs reveal the selective constraint on physiologically significant enzymes. P450s are present in virtually all tissues of marine invertebrates, although high levels usually are found in hepatic-like organs and steroidogenic tissues. High-throughput technologies result in the rapid acquisition of new marine invertebrate P450 sequences; however, the understanding of their function is poor. Based on analogy to vertebrates and insects, it is likely that P450s play a pivotal role in the physiology of marine invertebrates by catalyzing the biosynthesis of signal molecules including steroids such as 20-hydroxyecdysone (the molting hormone of crustaceans). The metabolism of many exogenous compounds including benzo(a)pyrene (BaP), pyrene, ethoxyresorufin, ethoxycoumarin and aniline is mediated by P450 enzymes in tissues of marine invertebrates. P450 gene expression, protein levels and P450 mediated metabolism of xenobiotics are induced by PAHs in some marine invertebrate species. Thus, regulation of P450 enzyme activity may play a central role in the adaptation of animals to environmental pollutants. Emphasis should be put on the elucidation of the function and regulation of the ever-increasing number of marine invertebrate P450s.     

Occurrence of sulfated galactans in marine angiosperms: evolutionary implications

We report for the first time that marine angiosperms (seagrasses) possess sulfated polysaccharides, which are absent in terrestrial and freshwater plants. The structure of the sulfated polysaccharide from the seagrass Ruppia maritima was determined. It is a sulfated D-galactan composed of the following regular tetrasaccharide repeating unit: [3-beta-D-Gal-2(OSO3)-1-->4-alpha-D-Gal-1-->4-alpha-D-Gal-1-->3-beta-D-Gal-4(OSO3)-1-->]. Sulfated galactans have been described previously in red algae and in marine invertebrates (ascidians and sea urchins). The sulfated galactan from the marine angiosperm has an intermediate structure when compared with the polysaccharides from these two other groups of organisms. Like marine invertebrate galactan, it expresses a regular repeating unit with a homogenous sulfation pattern. However, seagrass galactan contains the D-enantiomer of galactose instead of the L-isomer found in marine invertebrates. Like red algae, the marine angiosperm polysaccharide contains both alpha and beta units of D-galactose; however, these units are not distributed in an alternating order, as in algal galactan. Sulfated galactan is localized in the plant cell walls, mostly in rhizomes and roots, indicative of a relationship with the absorption of nutrients and of a possible structural function. The occurrence of sulfated galactans in marine organisms may be the result of physiological adaptations, which are not correlated with phylogenetic proximity. We suggest that convergent adaptation, due to environment pressure, may explain the occurrence of sulfated galactans in many marine organisms.