Genus Diadema Research Articles

Introgression of the gamete recognition molecule, bindin, in the sea urchin Diadema.

Hybridization is important in evolution, because it is a necessary (though not sufficient) step in the introgression of potentially adaptive variation between species. Bindin is a gamete recognition protein in echinoids and asteroids, capable of blocking cross-fertilization between species to varying degrees. Four species of the sea urchin genus Diadema are broadly sympatric in the Indo-Pacific: D. paucispinum, D. savignyi, D. clarki, and D. setosum. Data from three published studies, one of identification of hybrids through allozymes, one of the phylogeography of mitochondrial DNA, and one of the phylogeny of bindin, were combined to assess the degree of bindin introgression between these four species. I analyzed sequences of the ATPase 8 and ATPase 6 mitochondrial genes and of bindin, sampled throughout the species ranges, with an Isolation-Migration algorithm, IMa3. IMa3 uses a coalescent approach to produce Bayesian estimates of effective population sizes and gene flow between populations. The results showed that bindin alleles coalesce completely within the species bounds of D. clarki, and of D. setosum. The sister species D. paucispinum and D. savignyi, however, were estimated as having exchanged a bindin allele at an average of every one to two-and-a-half generations since they speciated from each other. As the allozyme study detected nine hybrids between three of these species in Okinawa (most of them between D. setosum and D. savignyi) in a single sample, hybrids between these species are produced, but bindin does not introgress. Therefore, bindin must not be efficient in blocking heterospecific fertilizations. Complete, or almost complete, reproductive isolation between species of Diadema must result from low hybrid fitness.

Phylogenetic Relationship of Diadema: Emphasis on The Two Distinct Clades of D. Setosum With The Inclusion of Long Spine Black Sea Urchin From Malaysian Borneo

Diadema urchins (family Diadematidae) are ecologically important bioindicators of coral reef ecosystems and seagrass beds. Diadema urchins which are widely distributed and broadcast spawners, have been frequently utilized as model invertebrate species for zoogeography research of the Indo-West Pacific region. So far, Malaysian Borneo, located at the geographic center of Maritime Southeast Asia, has been under-sampled. This study aims to fill this sampling gap and provide the first record of Diadema setosum from Malaysian Borneo using genetic diagnostics to conclusively establish the clade-level identity of the species. According to Cytochrome Oxidase I gene analysis, Diadema is monophyletic. Seven species of Diadema namely Diadema palmeri, Diadema clarki, Diadema mexicanum, Diadema antillarum, Diadema paucispinum, Diadema africanum, and Diadema savignyi, formed their subclades with strong bootstrap values, demonstrating interspecific variation. The findings of this study provide further evidence for the presence of two distinct monophyletic clades, with all D. setosum individuals forming a monophyletic clade that later split into two distinct subclades, dividing Red Sea population (D. setosum-b) and Indo-West Pacific populations (D. setosum-a), supported by a significant genetic divergence value ranging from 6.3% to 9.1%. This study also revealed notable levels of nucleotide and population subdivision between the D. setosum from the Indo-West Pacific and the Red Sea populations (Nst = 0.891; Fst = 0.886) with a low number of migrants per generation (Nm = 0.065). This may suggest geographic isolation due to ecological factors preventing each other from surviving in the territory of the other, or that the two clades of D. setosum were a separate species. Additional morphological and molecular analysis is required in the future to ascertain the level of divergence and further resolve the taxonomic confusion within the genus Diadema.

Development of Novel Pharmaceutical Forms of the Marine Bioactive Pigment Echinochrome A Enabling Alternative Routes of Administration.

Echinochrome A (EchA), a marine bioactive pigment isolated from various sea urchin species, is the active agent of the clinically approved drug Histochrome®. EchA is currently only available in the form of an isotonic solution of its di- and tri-sodium salts due to its poor water solubility and sensitivity to oxidation. Electrospun polymeric nanofibers have lately emerged as promising drug carriers capable of improving the dissolution and bioavailability of drugs with limited water solubility. In the current study, EchA isolated from sea urchins of the genus Diadema collected at the island of Kastellorizo was incorporated in electrospun micro-/nanofibrous matrices composed of polycaprolactone and polyvinylpyrrolidone in various combinations. The physicochemical properties of the micro-/nanofibers were characterized using SEM, FT-IR, TGA and DSC analyses. The fabricated matrices exhibited variable dissolution/release profiles of EchA, as evidenced in in vitro experiments using gastrointestinal-like fluids (pH 1.2, 4.5 and 6.8). Ex vivo permeability studies using the EchA-loaded micro-/nanofibrous matrices showed an increased permeation of EchA across the duodenum barrier. The results of our study clearly show that electrospun polymeric micro-/nanofibers represent promising carriers for the development of new pharmaceutical formulations with controlled release, as well as increased stability and solubility of EchA, suitable for oral administration, while offering the potential for targeted delivery.

Sea Urchen (Echinoidea) Diversity in the Coastal Area at Mawasangka District, Central Buton Regency

Sea urchins are marine invertebrates that are grouped in the Echinoidea class and Echinodermataphylum. Mawasangka is a district that has a large coastal area with a fairly good seagrass and coral reef ecosystem that plays an important role in the life cycle process of marine organisms, for instant as a habitat and food source for sea urchins. However, until now, information about the diversity of sea urchins in the coastal areas in Mawasangka District has not been reported. Thus, this research is very important. This research began with a location survey, field observation, and sampling. Supporting data such as temperature, pH, brightness, depth and salinity were also measured. The results showed that the number of species in 3 research locations in the coastal area of Mawasangka District was 5 species, consisting of 3 species from the genus Diadema, namely Diadema cytosum, Diadema antillarium, and Diadema savignyi, and 2 species from the Echinotrix genus, namely Echinothrix calamaris and Echinothrix diadema. The highest number of species diversity was found on the Pasi Kobungi beach. This happened because the habitat and environmental conditions at Pasi Kobungi Beach were very compatible for 5 species found. The species with the greatest abundance was sea urchins from the species of Diadema cytosum. It was found out that the coral reef substrate and seagrass in three research locations were important habitats for the growth of Diadema setosum and were easy to adapt to the environment. Due to the abundance of sea urchins from the Diadema cytosum species as well as many benefits of it for the environment, it can be concluded that the condition of the coastal area of Mawasangka District is still classified as healthy and well preserved.

Echinoderm research perspectives: A Central American bibliometric review

Introduction: Central America, a narrow strip of land dividing the Atlantic and Pacific oceans, has a high diversity of marine and terrestrial species. Echinoderms are one of the most diverse marine groups with 420 reported species. Objective: To summarize echinoderm research in Central America. Methods: We compiled the literature from SCOPUS, Web of Science, SciELO, Google Scholar, Biodiversity Heritage Library, the Internet Archive and the Smithsonian Library. Results: We found 324 publications dating from 1840 to 2020; the early studies had a strong taxonomic focus, but after the 1970s, ecology, evolution and reproduction gained prominence. Echinoidea is the most studied class (38% of publications) due to its use in evolutionary studies as well as the importance of the genus Diadema in reef ecology and dynamics. Conclusion: We recommend more research on fisheries management, conservation and environmental education; and greater integration of local and international research.

Struktur Komunitas Echinodermata pada Musim Barat dan Musim Peralihan I di Ekosistem Lamun Perairan Tanjung Benoa, Bali

Echinoderms in marine ecology have a role as deposit feeders. This shows the diversity of the Echinoderms phylum found in seagrass ecosystems. Seagrass beds serve as protection and a source of nutrients that maintain the food chain. Tanjung Benoa waters are located in the waters of South Bali which has a seagrass ecosystem. Echinoderms as invertebrate animals can be influenced by abiotic factors, namely salinity and temperature which are affected by the season. This study aims to determine changes in the structure of the Echinodermata community in the western and transitional seasons I in seagrass ecosystems and determine the environmental factors that influence the structure of the Echinoderms community in the waters of Tanjung Benoa. Echinoderms data collection method used is the Underwater Visual Census (UVC) method. Data is taken by using purposive sampling technique. The results showed that in both seasons, the western season and the transitional season I, the phylum of Echinoderms found consisted of 4 classes namely Holothuroidea, Ophiuroidea, Echinoidea and Asteroidea. The diversity index and uniformity of the Ecinodermal phylum found in both seasons shows stable diversity and uniformity. Based on the index of dominance there is one genus that dominates, namely the genus Diadema. Based on the analysis of PCA in the west season, the density of Echinoderms is influenced by phosphate, nitrate, DO, salinity, pH and temperature. Whereas in the transitional season I density is influenced by phosphate, salinity, temperature, nitrate and pH.

New data on distribution of muscle and serotonin-containing cells in larvae of diadematid sea urchins from Nha Trang Bay (South China Sea)

ABSTRACT With staining by antibodies, the general morphology and topography of serotonin-containing cells (SCC) and cells expressing high levels of actin have been compared between three developmental stages in ‘Echinopluteus transversus’ type larvae of sea urchins from genus Diadema. At an early pluteus stage single SC cells are found in the preoral buccal lobe of the pluteus as a component of the ciliary band. The cells expressing high levels of actin form the oesophageal muscles. At the middle pluteus stage, SC cells form two ganglion-shaped clusters in the anterior part of the larva, as well as a distributed neuropil running along the ciliary band; the bodies of the SC cells are included in the ciliary band epithelium. At this developmental stage the oesophageal musculature and little dilator muscles at the mouth were visualized. In late pluteus stage, the ganglion-shaped groups of SC cells merge into one in the anterior part of the larva; the distributed neuropil in the ciliary band is preserved. At this developmental stage, the cells expressing high levels of actin are in the oesophagus muscles and in three separate well developed muscles: ventral adductor muscle, dorsal adductor muscle, and abductor muscle. These muscles carry out movements of the larval arms.

Unexpected discovery of Diadema clarki in the Coral Triangle

Sea urchins of the genus Diadema, key herbivores in coral reef ecosystems, also provide habitat for other organisms. Our research extended Diadema biogeography in seaways east and west of Sulawesi and identified Diadema species associated with the endemic Banggai cardinalfish (Pterapogon kauderni) using field surveys and molecular DNA barcoding methods. Field observations (20 sites, n = 11,223) found urchins with morphological phenotypes typical of Diadema setosum (≈ 74%, all sites), D. savignyi (≈ 24%, 19 sites) and atypical or mixed traits (≈ 2%, 19 sites). Distribution of these phenotype groups across the three main habitat types (i.e. coral reef, reef flat and seagrass beds) differed significantly (χ2 = 533.03, p < 2.2e−16), indicating overlapping but non-equivalent ecological niches. Pterapogon kauderni associated with all urchin morphological phenotypes present. Diadema mtDNA CO1 sequences were obtained from tissue samples collected (4 sites, n = 62) from specimens with typical D. savignyi and D. setosum phenotypes. Phylogenetic tree analysis resolved the sequences into four clades. Three clades from our analysis were identified as D. savignyi, D. setosum and D. clarki based on additional sequences obtained from GenBank. This unexpected first record of D. clarki mtDNA in the Coral Triangle implies a substantial extension of the known range of this recently resurrected species. Our findings indicate the occurrence and/or introgression of D. clarki may be widespread, and misidentification of Diadema urchins based on external morphology may be relatively common. Further research is required to determine the distribution and functional roles of Indo-Pacific Diadema species, contributing to our understanding of processes underpinning biodiversity.

How to distinguish three sea urchin species of the genus Diadema in Japan.

How to distinguish three sea urchin species of the genus Diadema in Japan.

A Tale of Two Urchins - Implications for In-Situ Breeding of the Endangered Banggai Cardinalfish (Pterapogon kauderni)

The endangered Banggai cardinalfish Pterapogon kauderni , endemic to the Banggai Archipelago in Central Sulawesi, Indonesia, is a national and global priority conservation species. To support stock recovery based on in-situ breeding, using the symbiosis between the Banggai cardinalfish and its microhabitat (especially urchins of Genus Diadema ), specific research objectives were: (i) identify the Diadema species associated with Banggai cardinalfish in the wild; (ii) investigate Banggai cardinalfish preference between these Diadema species. Belt transect data (5 sites) found wild Banggai cardinalfish of all size classes associated with Diadema setosum and Diadema savign yi. Preference trials were conducted in a controlled environment (concrete tanks) with three replicates. Nine sub-adult Banggai cardinalfish (35-42 mm SL), 12 D. setosum and 12 D. savigny i were placed in each tank. Banggai cardinalfish association ( D. savignyi, D. setosum , none) was recorded hourly (06:00-18:00) for three days and results analysed in RStudio-1.0.143. Banggai cardinalfish did not show significant preference for either D. savignyi or D. setosum . These results indicate that D. savignyi and D. setosum can be used impartially in further research on in-situ breeding to facilitate recovery of Banggai cardinalfish stocks. However stock recovery measures should consider genetic connectivity and the natural balance between the two urchin species.

Evolution of gamete attraction molecules: evidence for purifying selection in speract and its receptor, in the pantropical sea urchin Diadema.

Many free-spawning marine invertebrates, such as sea urchins, lack any courtship or assortative mating behavior. Mate recognition in such cases occur at the gametic level, and molecules present on the sperm and egg are major determinants of species-specific fertilization. These molecules must also coevolve in relation to each other in order to preserve functional integrity. When sea urchins release their gametes in seawater, diffusible molecules from the egg, termed sperm-activating peptides, activate and attract the sperm to swim toward the egg, initiating a series of interactions between the gametes. Although the compositions and diversity of such sperm-activating peptides have been characterized in a variety of sea urchins, little is known about the evolution of their genes. Here we characterize the genes encoding the sperm-activating peptide of the egg (speract) and its receptor on the sperm, and examine their evolutionary dynamics in the sea urchin genus Diadema, in the interest of determining whether they are involved in reproductive isolation between the species. We found evidence of purifying selection on several codon sites in both molecules and of selectively neutral evolution in others. The diffusible speract peptide that activates sperm is invariant across species, indicating that Diadema egg peptides do not discriminate between con- and hetero-specific sperm at this stage of the process. Speract and its receptor do not contribute to reproductive isolation in Diadema.

On the fourth Diadema species (Diadema-sp) from Japan.

Four long-spined sea urchin species in the genus Diadema are known to occur around the Japanese Archipelago. Three species (D. savignyi, D. setosum, and D. paucispinum) are widely distributed in the Indo-Pacific Ocean. The fourth species was detected by DNA analysis among samples originally collected as D. savignyi or D. setosum in Japan and the Marshall Islands and tentatively designated as Diadema -sp, remaining an undescribed species. We analyzed nucleotide sequences of the cytochrome oxidase I (COI) gene in the “D. savignyi-like” samples, and found all 17 individuals collected in the mainland of Japan (Sagami Bay and Kyushu) to be Diadema-sp, but all nine in the Ryukyu Archipelago (Okinawa and Ishigaki Islands) to be D. savignyi, with large nucleotide sequence difference between them (11.0%±1.7 SE). Diadema-sp and D. savignyi shared Y-shaped blue lines of iridophores along the interambulacrals, but individuals of Diadema-sp typically exhibited a conspicuous white streak at the fork of the Y-shaped blue iridophore lines, while this feature was absent in D. savignyi. Also, the central axis of the Y-shaped blue lines of iridophores was approximately twice as long as the V-component in D. savignyi whereas it was of similar length in Diadema-sp. Two parallel lines were observed to constitute the central axis of the Y-shaped blue lines in both species, but these were considerably narrower in Diadema-sp. Despite marked morphological and genetic differences, it appears that Diadema-sp has been mis-identified as D. savignyi for more than half a century.

Diadema ascensionisMortensen, 1909 (Echinodermata: Echinoidea) is not restricted to Oceanic Islands: evidence from morphological data

The genus Diadema presently consists of seven species, two of which are known from the Brazilian coast: D. antillarum and D. ascensionis. The first is usually known for shallow coastal areas, while the second was apparently restricted to oceanic islands. In February 2011, a dense population of D. ascensionis was observed on the coastal reefs of Praia do Francês (Alagoas State, northeastern Brazil). Five specimens were collected and transported to the laboratory where morphological studies of the test and pedicellariae were conducted. Subsequently, visits were made to scientific collections in order to compare and confirm species identifications. Our observations confirm the presence of tridentate pedicellariae with narrow and strongly curved valves. The axial cavity in the tips of the spines is filled with dense nonreticular tissue. This taxonomic data confirms the occurrence of D. ascensionis in coastal areas. On the coastal reefs of Praia do Francês, animals were observed from the beach to the reef formations about 200 m offshore in areas with a sandy substrate and in reef cavities, usually in clear and well illuminated waters. Solitary individuals or groups of up to 15 individuals formed dense populations in the area. We stress the importance of pedicellariae for the specific identification of the Diadematidae, considering that they are quite constant and reliable at this taxonomic level. Our results demonstrate that D. ascensionis is not restricted to insular environments and that this species may be common in shallow coastal habitats.

Temporal variation of the sea urchin (Diadema mexicanum) population density at Bahias de Huatulco, Western Mexico

Sea urchins of the genus Diadema play an important role as controlers of algal growth in coral reef and rocky reef communities, but high densities cause bioerosion of the reef framework. Between January 2006 and February 2007 (except April, July and August), population densities and mean test diameter of Diadema mexicanum were determined at Isla Montosa, La Entrega, Isla Cacaluta and San Agustin, Bahias de Huatulco, Mexico. Mean density of the sea urchins was relatively constant through time at all localities: lowest at San Agustin (0.26±0.13 ind.m-2) and highest at La Entrega (4.17±1.4 ind.m-2). There were significant differences between La Entrega and other localities. Mean test diameter ranged between 4.41±0.88 cm (Isla Cacaluta) and 4.72±0.27 (San Agustin), and did no vary significantly between localities, but there were monthly variations. Test diameter agrees with other studies. The calculated amount of CaCO3 removed by D. mexicanum showed variations between localities. The lowest rate of bioerosion occurred at San Agustin (0. 25 kg.m-2.yr-1 ), and the highest at La Entrega (4 kg.m-2.yr-1). The recent urchin population decrease means a reduction in their removal of coral CaCO3: 5.55% to 2.36% at Isla Cacaluta, 5.08% to 1.40% at San Agustin and 16.59% to 3.08% at Isla Montosa. The only locality where bioerosion increased was La Entrega, from 27.04 % to 33.05 %. This reduction of urchin activities could be beneficial for coral reef growing and recovery from stress, nevertheless it could also signify an increase in algal biomass and competition with corals for light and space. We recommend a permanent monitoring and evaluation of population densities of D. mexicanum and fishes, as well as coral and algal cover at the area, to discern if changes in sea urchin densities in Bahias de Huatulco are a continuous phenomenon, or part of a natural cycle of increments and reductions. Rev. Biol. Trop. 56 (Suppl. 3): 255-263. Epub 2009 January 05.

POPULATION STRUCTURE AND SPECIATION IN TROPICAL SEAS: GLOBAL PHYLOGEOGRAPHY OF THE SEA URCHIN DIADEMA

Abstract.— The causes of speciation in the sea are rarely obvious, because geographical barriers are not conspicuous and dispersal abilities or marine organisms, particularly those of species with planktonic larvae, are hard to determine. The phylogenetic relations of species in cosmopolitan genera can provide information on the likely mode of their formation. We reconstructed the phylogeny of the pantropical and subtropical sea urchin genus Diadema, using sequences of mitochondrial DNA from 482 individuals collected around the world, to determine the efficacy of barriers to gene flow and to ascertain the history of possible dispersal and vicariance events that led to speciation. We also compared 22 isozyme loci between all described species except D. palmeri. The mitochondrial DNA data show that the two deepest lineages are found in the Indian and West Pacific Oceans. (Indo-Pacific) Diadema setosum diverged first from all other extant Diadema, probably during the initiation of wide fluctuations in global sea levels in the Miocene. The D. setosum clade then split 3-5 million years ago into two clades, one found around the Arabian Peninsula and the other in the Indo-West Pacific. On the lineage leading to the other species of Diadema, the deepest branch is composed of D. palmeri, apparently separated when the climate of New Zealand became colder and other tropical echinoids at these islands went extinct. The next lineage to separate is composed of a currently unrecognized species of Diadema that is found at Japan and the Marshall Islands. Diadema mexicanum in the eastern Pacific separated next, whereas D. paucispinum, D. savignyi, and D. antillarum from the western and central Atlantic, and (as a separate clade) D. antillarum from the eastern Atlantic form a shallow polytomy. Apparently, Indo-Pacific populations of Diadema maintained genetic contact with Atlantic ones around the southern tip of Africa for some time after the Isthmus of Panama was complete. Diadema paucispinum contains two lineages: D. paucispinum sensu stricto is not limited to Hawaii as previously thought, but extends to Easter Island, Pitcairn, and Okinawa; A second mitochondrial clade of D. paucispinum extends from East Africa and Arabia to the Philippines and New Guinea. A more recent separation between West Indian Ocean and West Pacific populations was detected in D. setosum. Presumably, these genetic discontinuities are the result of water flow restrictions in the straits between northern Australia and Southeast Asia during Pleistocene episodes of low sea level. Diadema savignyi is characterized by high rates of gene flow from Kiribati in the central Pacific all the way to the East African Coast. In the Atlantic, there is a biogeographic barrier between the Caribbean and Brazil, possibly caused by fresh water outflow from the Amazon and the Orinoco Rivers. Diadema antillarum populations of the central Atlantic islands of Ascension and St. Helena are genetically isolated and phylogenetically derived from Brazil. Except for its genetic separation by the mid-Atlantic barrier, Diadema seems to have maintained connections through potential barriers to dispersal (including the Isthmus of Panama) more recently than did Eucidaris or Echinometra, two other genera of sea urchins in which phylogeography has been studied. Nevertheless, the mtDNA phylogeography of Diadema includes all stages expected from models of allopatric differentiation. There are anciently separated clades that now overlap in their geographic distribution, clades isolated in the periphery of the genus range that have remained in the periphery, clades that may have been isolated in the periphery but have since spread towards the center, closely related clades on either side of an existing barrier, and closely related monophyletic entities on either side of an historical barrier that have crossed the former barrier line, but have not attained genetic equilibrium. Except for D. paucispinum and D. savignyi, in which known hybridization may have lodged mtDNA from one species into the genome of the other, closely related clades are always allopatric, and only distantly related ones overlap geographically. Thus, the phylogenetic history and distribution of extant species of Diadema is by and large consistent with allopatric speciation.

Hybridization and introgression between Indo-Pacific species of Diadema

We present the first case of hybridization between echinoid species evaluated through genetic markers and morphology. We examined the three tropical Indo-Pacific species of the genus Diadema: D. paucispinum A. Agassiz, D. savignyi (Audouin) Michelin and D. setosum (Leske). Specimens morphologically intermediate between two of these species, D. savignyi and D. setosumhave previously been noted. Fertile hybrids have also been produced in the laboratory. To determine extent of hybridization, we first assayed the allozyme products of 22 loci in individuals which, on the basis of morphology and collection locality, could be unambiguously assigned to one of the three species. We found four loci that were either diagnostic or semi-diagnostic between D. setosum and the other two species, and one locus semi-diagnostic between D. savignyi and D. paucispinum.We then assayed individuals of intermediate morphology to find out whether they had hybrid genotypes. In the Ryukyu Islands, where D. setosum and D. savignyi coexist, we found one specimen which on the basis of all four diagnostic loci was an F1 hybrid, and several individuals that could be either F2 (or later-generation) hybrids or progeny of backcrosses.We also found one individual that on both genetic and morphological grounds appeared to belong to D. paucispinum (even though this spcies has only been reported from Hawaii and Kiribati) and three other individuals that carried alleles characteristic of D. paucispinum. Thus, previous reports of hybridization between D. setosum and D. savignyi were correct; it is also possible that larvae of D. paucispinum occasionally arrive at localities outside Hawaii, reach sexual maturity, and hybridize with the other two species. Counts of pure and hybrid morphotypes in other populations across the western tropical Pacific revealed a low but widespread incidence of apparent F1 hybrids and backcrosses of D.savignyi and D. setosum. However, the existence of diagnostic or semi-diagnostic loci, low interspecific gene-flow estimates based on F st statistics, and the lack of Hardy-Weinberg or linkage disequilibria among individuals of pure morphology all suggest that gene introgression between the three species is limited.

Sexual dimorphism and food habits of the clingfish, Diademichthys lineatus, and its dependence on host sea urchin

Stomach contents of the clingfish Diademichthys lineatus, 10–56 mm standard length, revealed changes in food habits with growth and sexual differences. Soon after settlement, D. lineatus obtained food from their host sea urchin (genus Diadema) and other associated symbionts. They became less dependent on the host with growth. The juveniles ate pedicellariae and sphaeridia of the host and commensal copepods, whereas the adult fish ate burrowing bivalves in corals as well as tube feet of their host and eggs of a commensal shrimp. The young fish were transitional in their food habits. The change in food habits of the fish coincided with behavioral changes; i.e. enlargement of home ranges and less dependency on the host. The adult females, having a longer snout, ate shrimp eggs and bivalves more frequently than the adult males, which ate tube feet of the host more often than the females did. Sexual difference in food habits was apparent after the sex of the fish became identifiable by comparing snout shapes. The polygynous mating system of this species suggests that conspicuous sexual dimorphism might have developed under sexual selection. However, niche partitioning of food is also likely to be related to this sexual dimorphism.

CHAMBERS WITHIN THE VALVE OFDIADEMA, GEN. NOV.

A new genus Diadema is described, which is a naviculoid diatom with hollow parietal chambers within the valve wall and an unusual valve structure. The only known species is D. luxuriosa, formerly included in Navicula. The structure of the parietal chambers is compared with analogous features of Mastogloia, Dictyoneis, Diploneis, and Scoliotropis.

Diadema

The new genus Diadema is described for six species of alpine pyrenomycetes from the Himalayas and western North America: Diadema acuta on Poa from California and on Trisetum from Kashmir, Diadema cincta on Carex from Punjab, Diadema curta on Biebersteinia (Gentianaceae) from Kashmir, Diadema hexamera on Poa from California, Diadema obtusa on Potentilla and Trisetum from Kashmir, and Diadema tetramera on various grasses and Juncus from California.

Genetic Analysis of Two Sympatric Sea Urchins from Genus Diadema (Echinodermata: Echinoidea: Diadematidae) from Malaysian Borneo

Genus Diadema (Echinoidea: Diadematidae) has been reported to be the most widespread and ecologically important shallow water tropical sea urchins. Morphological variations and species distributions are complicated to elucidate due to complexity in making reliable identifications. Genus Diadema had involved in many debates, particularly on the mode of speciation and the specific status of Diadema setosum and Diadema savignyi. Therefore, relationships among Diadema species found in Malaysian Borneo have been examined using 16S rRNA gene analysis. Monophyletic clade of genus Diadema with respect to the outgroup was obtained with high bootstrap values of 100% (MP), 100% (NJ), 100% (ML) and Bayesian Posterior Probability is equal to 1.00. Two monophyletic clades were apparent separating D. setosum (Clade I) and D. savignyi (Clade II), with strong support of 100% (MP), 100% (NJ), 80% (ML) and Bayesian Posterior Probability is equal to 1.00. In addition, high genetic variation among species had been recorded (9.85%), suggesting that D. setosum and D. savignyi are two distinct entities. Furthermore, D. setosum and D. savignyi are sympatric species based on their distribution and overlapping ranges in Malaysian Borneo.