Sipuncula Research Articles

Characterization of metabolomic differences in peanut worm Sipunculus nudus between breeding and nonbreeding seasons

Peanut worm, Sipunculus nudus, is an important economic and ecological species. This study aims to characterize differences in the coelomic fluid of S. nudus between breeding and nonbreeding seasons. Animals were obtained in July and November. The diameter of oocytes was measured and analyzed. Results showed that the number of oocytes formed a primary peak at a diameter of approximately 160 μm in July, while almost all oocytes were below 50 μm in November. A metabolomics approach based on LC–MS and GC–MS was used to investigate differences in coelomic fluid and gain insights into the mechanisms underlying the oocyte development of S. nudus. In the metabolomics assay, 44 and 32 significantly differential metabolites were obtained via LC–MS and GC–MS (VIP > 1 and P < 0.1), respectively. S. nudus changed its metabolic status under different development conditions. The analysis of further integrated key metabolic pathways showed that S. nudus possessed different capabilities for valine, leucine, and isoleucine biosynthesis; phenylalanine, tyrosine, and tryptophan biosynthesis; aminoacyl-tRNA biosynthesis; butanoate metabolism; tyrosine metabolism; alanine, aspartate, and glutamate metabolism; galactose metabolism; and ubiquinone and other terpenoid-quinone biosynthesis between breeding and nonbreeding seasons. S. nudus may exhibit high anabolic ability to store nutrients and hold the high activity of neurotransmitter precursors to regulate oocyte development during the breeding season. This metabolomics study is the first to identify crucial metabolites and key pathways to understand the metabolic mechanism of oocyte development. The results provide theoretical basis for artificial breeding of S. nudus.

Anti-inflammatory action of two novel peptides derived from peanut worms (Sipunculus nudus) in lipopolysaccharide-induced RAW264.7 macrophages.

Peanut worm (Sipunculus nudus Linn.) protein was hydrolyzed by three proteases, and NO scavenging activity of the protein hydrolysates was evaluated. The hydrolysate obtained using Alcalase® showed the highest NO scavenging activity. This hydrolysate was fractionated using 10-, 5-, and 3 kDa molecular weight cut-off membranes, and the lowest MW fraction (<3 kDa) exhibited the highest NO scavenging activity. The <3 kDa fraction was further purified by gel filtration and high-performance liquid chromatographies. The peptides in the HPLC fraction with the strongest anti-NO activity were identified by quadrupole-time-of-flight mass spectrometry as LSPLLAAH (821.48 Da) and TVNLAYY (843.42 Da). Both peptides and the corresponding pure synthetic peptides inhibited NO production by RAW 264.7 macrophages without cytotoxicity. Quantitative real-time RT-PCR analysis showed that peptides LSPLLAAH and TVNLAYY reduced expression of proinflammatory cytokine genes iNOS, IL-6, TNF-α, and COX-2 in RAW 264.7 macrophages, suggesting that these peptides are novel anti-inflammatory candidates.

Variable-Temperature ESI-IMS-MS Analysis of Myohemerythrin Reveals Ligand Losses, Unfolding, and a Non-Native Disulfide Bond.

Variable-temperature electrospray ionization combined with ion mobility spectrometry (IMS) and mass spectrometry (MS) techniques are used to monitor structural transitions of the protein myohemerythrin from peanut worm in aqueous ammonium acetate solutions from ∼15 to 92 °C. At physiological temperatures, myohemerythrin favors a four-helix bundle motif and has a diiron oxo cofactor that binds oxygen. As the solution temperature is increased from ∼15 to 35 °C, some bound oxygen dissociates; at ∼66 °C, the cofactor dissociates to produce populations of both folded and unfolded apoprotein. At higher temperatures (∼85 °C and above), the IMS-MS spectrum indicates that the folded apoprotein dominates, and provides evidence for stabilization of the structure by formation of a non-native disulfide bond. In total, we find evidence for 18 unique forms of myohemerythrin as well as information about the structures and stabilities of these states. The high-fidelity of IMS-MS techniques provides a means of examining the stabilities of individual components of complex mixtures that are inaccessible by traditional calorimetric and spectroscopic methods.

Annual reproductive cycle of peanut worm, Sipunculus nudus from Thailand

Annual reproductive cycle of peanut worm, Sipunculus nudus from Thailand

Digestive solubilization of particle-associated arsenate by deposit-feeders: The roles of proteinaceous and surfactant materials

Solubilization of arsenate in guts of deposit-feeders is a key process for their dietary uptake of arsenate from contaminated sediments. The present study explored this digestive solubilization with in vitro extraction experiments that quantified arsenic (As) release from substrates (natural sediment and As-enriched iron oxides) in the presence of various digestive agents (proteins, amino acids and surfactants collected from gut fluid of a sipunculan worm). To investigate potential mechanisms for the influence of digestive agents, analyses determined correlations between As and Fe concentrations, the size distribution of the As bound to the digestive agents, and the adsorption of the digestive agents on the substrates. Both the digestive surfactants and proteinaceous materials increased arsenate mobilization, with the surfactants enhancing the effects of the proteinaceous materials. Arsenate reduction and reductive dissolution of iron oxides were not observed and correlations between the concentrations of released As and Fe were weak. These findings indicate that dissolution release of Fe did not appear to be the main route by which the digestive agents mobilized particle-associated As. Most of the released As (>70%) was distributed in the <10 kDa fraction of the digestive agents, showing that the As mobilization was also not caused by complexation with proteins in the digestive agents. In contrast, adsorption of the digestive agents occurred along with the release of arsenate from the arsenate-rich substrates, suggesting that competitive adsorption was the mechanism by which the digestive agents mobilized sedimentary arsenate. Our work demonstrated that the presence of digestive surfactants significantly enhances arsenate availability during deposit feeding.

Bioturbation of peanut worms Sipunculus nudus on the composition of prokaryotic communities in a tidal flat as revealed by 16S rRNA gene sequences.

To understand the impacts of peanut worms Sipunculus nudus on the prokaryotic community composition in a tidal flat, an onsite investigation was conducted in Suixi in the Beibu Gulf (109.82E, 21.35N) in the burrow sediments, non‐burrow sediments and the sediments without peanut worm disturbance (control). The16S rRNA gene Illumina MiSeq sequencing was used to investigate the microbial communities and their response to bioturbation by S. nudus in a sandy tidal flat. A total of 18 bacteria phyla were detected, and Proteobacteria and Cyanobacteria constituted the majority of the prokaryotic community in the samples. The distribution of the relative abundances of genera showed that approximately 6.99%–17% of the reads in the samples were classified into 25 known genera. Sulfate‐reducing bacteria (Desulfococcus and Desulfosarcina) were the most abundant taxa, followed by Thermodesulfovibrionaceae LCP‐6, indicating that sulfate reduction is the main process in the sandy tidal flat. The abundances of Desulfococcus, LCP‐6 and Cyanobacterium in the non‐burrow sediment were greater than in the burrow sediment, suggesting that the anoxic condition is more suitable for Desulfococcus and LCP‐6 when the activity of S. nudus is absent. The biomass of Cyanobacterium was decreased by the feeding bioturbation of S. nudus. Meanwhile, the relative abundance of the Bacteroidetes Luteimonas in the burrow sediments was significantly greater than in the non‐burrow sediment, and there was a strong relationship between S. nudus bioturbation and increased in oxygen contents and oxidation‐reduction potentials in the burrow sediment. The abundances of Desulfococcus and LCP‐6 were greater in the middle layer (20–30 cm) than in the top layer in the non‐burrow sediment. However, the middle and bottom layers (20–30, 30–40 cm) had higher abundances of these genera than did the upper layers (0–10, 10–20 cm) in the burrow sediments. The abundances of the Fusobacteria Propionigenium and the Spirochaetes Spirochaeta were greater in the middle and bottom layers (20–30 cm, 30–40 cm) than in the top layers (0–10, 10–20 cm) in the burrow sediment, but this phenomenon was not found in the non‐burrow sediment. This study demonstrates that bioturbation by S. nudus plays an important role in reshaping the bacterial community composition in intertidal regions.

A report on two large collections of the squat lobster Munidopsis platirostris (Decapoda, Anomura, Munidopsidae) from the Caribbean, with notes on their parasites, associates, and reproduction

ABSTRACTThe reproduction and parasite associates of the squat lobster Munidopsis platirostris (A. Milne Edwards and Bouvier, 1894) were investigated based on collections made in the Bahamas and Curaçao with grassmat and bundled fishing net traps used to collect sipunculan worms and other small invertebrates. Size of ovigerous M. platirostris was significantly correlated with clutch size for females from both localities but females from the Bahamas produced significantly more eggs (on average 10.1 eggs/clutch) than females from Curaçao (on average 6.6 eggs/clutch). Early embryos of M. platirostris from the Bahamas were 0.74–0.82 mm in diameter, similar to some other species of Munidopsidae as well as Chirostylidae. Two species of crustaceans, another squat lobster and a leptostracan, as well as a limpet mollusc, were collected with M. platirostris in the Bahamas, while a sipunculan was an associated species in a Curaçao collection. One specimen of M. platirostris had an unidentified cryptoniscoid epicaridean isopod, possibly representing a new genus and species. Two specimens of M. platirostris each had one rhizocephalan externa of a species belonging to Lernaeodiscus Müller, 1862 but their morphology does not match that of L. schmitti Reinhard, 1950, the only species in the genus known from squat lobsters in the western Atlantic. Additional materials and tools, such as DNA analysis, are needed to describe these potentially new parasites and we suggest that use of these traps may be an effective method to obtain additional samples.

Population density of the peanut worm Siphonosoma australe australe (Keferstein, 1865) (Sipunculus: Phascolosomatidae) in the mangrove forest of Gianh river, Quang Binh province

The peanut worm, Siphonosoma australe australe (Keferstein, 1865), is a non-segmented worm, with a coelom, most live in areas of shallow water, tidal areas or the sea. Currently, the number of individuals in Peanut worm populations are declining considerably due to over-exploitation and habitat degradation. However, information on individual density and biomass of Peanut worm populations in Vietnam is still lacking, as is information on environmental factors affecting them. This study was carried out at various sites in the lower reaches of mangrove forest of the Gianh river, Quang Binh province. We calculated individual and hole densities per month by counting the number of individuals and holes according to each site area. We found significant differences (p ≤ 0.037) among sampled sites in hole density (from 1.43 to 2.54 holes/m2, average of 1,96 holes/m2), individual number (from 45 to 81 individuals, average of 62 individuals/site area), and biomass (from 20.27 to 51.16 g/m2, average of 34.57 g/m2). However, individual density (from 0.51 to 0.98 individuals/m2, average of 0.68 individuals/m2) was not significantly different among sites. Water temperature, pH, and salinity have the significant effect on individual and hole densities, individual number, and biomass of peanut worms (p ≤ 0.001; excepting water temperature affects the biomass of peanut worms). Excepting biomass, average individual and hole densities, as well as individual number of peanut worms, were greater in the dry season than in the rainy season (p &lt; 0.0001).&#x0D; Keywords: Siphonosoma australe australe, biomass, density, mangrove forest, peanut worms, Gianh river.&#x0D; Citation: Nguyen Thi My Huong, Ngo Dac Chung, Le Huy Ba, 2018. Population density of the peanut worm Siphonosoma australe australe (Keferstein, 1865) (sipunculus:phascolosomatidae) in the mangrove forest of gianh river, Quang Binh province. Tạp chí Sinh học, 40(2): 138–144. https://doi.org/10.15625/0866-7160/v40n2.8511.&#x0D; *Corresponding author: myhuong_s4qt@quangbinh.edu.vn

Population density of the peanut worm Siphonosoma australe australe (Keferstein, 1865) (Sipunculus: Phascolosomatidae) in the mangrove forest of Gianh river, Quang Binh province

The peanut worm, Siphonosoma australe australe (Keferstein, 1865), is a non-segmented worm, with a coelom, most live in areas of shallow water, tidal areas or the sea. Currently, the number of individuals in Peanut worm populations are declining considerably due to over-exploitation and habitat degradation. However, information on individual density and biomass of Peanut worm populations in Vietnam is still lacking, as is information on environmental factors affecting them. This study was carried out at various sites in the lower reaches of mangrove forest of the Gianh river, Quang Binh province. We calculated individual and hole densities per month by counting the number of individuals and holes according to each site area. We found significant differences (p ≤ 0.037) among sampled sites in hole density (from 1.43 to 2.54 holes/m2, average of 1,96 holes/m2), individual number (from 45 to 81 individuals, average of 62 individuals/site area), and biomass (from 20.27 to 51.16 g/m2, average of 34.57 g/m2). However, individual density (from 0.51 to 0.98 individuals/m2, average of 0.68 individuals/m2) was not significantly different among sites. Water temperature, pH, and salinity have the significant effect on individual and hole densities, individual number, and biomass of peanut worms (p ≤ 0.001; excepting water temperature affects the biomass of peanut worms). Excepting biomass, average individual and hole densities, as well as individual number of peanut worms, were greater in the dry season than in the rainy season (p &lt; 0.0001).&#x0D; Keywords: Siphonosoma australe australe, biomass, density, mangrove forest, peanut worms, Gianh river.&#x0D; Citation: Nguyen Thi My Huong, Ngo Dac Chung, Le Huy Ba, 2018. Population density of the peanut worm Siphonosoma australe australe (Keferstein, 1865) (sipunculus:phascolosomatidae) in the mangrove forest of gianh river, Quang Binh province. Tạp chí Sinh học, 40(2): 138–144. https://doi.org/10.15625/0866-7160/v40n2.8511.&#x0D; *Corresponding author: myhuong_s4qt@quangbinh.edu.vn

The complete mitochondrial genome of the cryptic species in peanut worm Sipunculus nudus (Sipuncula, Sipunculidae) from Beibu Bay

The peanut worm Sipunculus nudus is an economic important species in the fishery and aquaculture in Indo-West Pacific. However, it is a species complex consisting of cryptic species, which can be difficult to identify based on morphology. Here, we report the complete mitochondrial genome sequence of S. nudus from Beibu Bay. The mitogenome has 15,375 base pairs and made up of total of 38 genes (13 protein-coding, 23 transfer RNAs, and two ribosomal RNAs), and a putative control region. There were 5948 mutations sites between Chinese and French populations. This study adds a distinct mitogenome of S. nudus, and will provide useful genetic information for future genetic variation identification and genetic diversity evaluation of this economic valuable marine benthic invertebrate.

Molecular Detection of Eukaryotic Diets and Gut Mycobiomes in Two Marine Sediment-Dwelling Worms, &lt;i&gt;Sipunculus nudus&lt;/i&gt; and &lt;i&gt;Urechis unicinctus&lt;/i&gt;

The present study aimed to reveal the eukaryotic diets of two economically important marine sediment-inhabiting worms, Sipunculus nudus (peanut worm) and Urechis unicinctus (spoon worm), using clone libraries and phylogenetic analyses of 18S rRNA genes. Fungal rDNA was also targeted and analyzed to reveal mycobiomes. Overall, we detected a wide range of eukaryotic phylotypes associated with the larvae of S. nudus and in the gut contents of both worms. These phylotypes included ciliates, diatoms, dinoflagellates, eustigmatophytes, placidids, oomycetes, fungi, nematodes, flatworms, seaweeds, and higher plants. Oomycetes were associated with the planktonic larvae of S. nudus. The composition of eukaryotic diets shifted greatly across the larval, juvenile, and adult stages of S. nudus, and among different gut sections in U. unicinctus, reflecting lifestyle changes during the ontogeny of the peanut worm and progressive digestion in the spoon worm. Malassezia-like fungi were prevalent in mycobiomes. Epicoccum and Trichosporon-related phylotypes dominated mycobiomes associated with larval individuals and in the gut contents of adults, respectively. The gut mycobiome of S. nudus was successively characterized through the midgut, aspiratory intestines, hindgut, and rectum as having a high proportion of Climacodon-Rhizochaete, Ceriporiopsis, Cladosporium-Pseudomicrostroma, and Malassezia-related species in the libraries. These results emphasize the dynamics of diets and gut mycobiomes in marine benthic animals.

Deep-water Bryozoa from the Kuril Basin, Sea of Okhotsk

Benthic samples collected at six stations in the Kuril Basin, Sea of Okhotsk, at depths of 3301 to 3366 m, and at two northwestern Pacific stations in Bussol Strait and on the western slope of the Kuril-Kamchatka Trench, at depths 2267 and 3374 m, yielded three cyclostome, two ctenostome, and two cheilostome bryozoan species. Among these, Oncousoecia viskovae sp. nov. is the deepest record for a species in this genus. Triticella maiorovae sp. nov., a symbiont on a sipunculid worm, is the second species of the genus discovered in the northwestern Pacific. Our study yielded the deepest records for Bicrisia abyssicola and Buchneria teres, and the first records for Triticella minini and B. teres from the Sea of Okhotsk. The proportion of cheilostomes in the samples was much lower than expected from previous studies, although the sample size and total diversity were also low. Dead colonies of four cheilostome species, Einhornia arctica, Porella alba, Cryptosula zavjalovensis and Cheilopora praelucida, were found encrusting pebbles at two abyssal sites; we interpret these as allochthonic elements due to ice transport of pebbles from shallow waters to the Kuril Basin. Stenobathic and eurybathic species common to both the Kuril Basin and northwestern Pacific indicate connectivity between deep water faunas in these adjacent regions.

The complete mitogenome of a peanut worm Phascolosoma pacificum (Sipuncula, Phascolosomatida, Phascolosomatidea)

Sipuncula (peanut worms) is a traditional phylum which consists of unsegmented bilateral symmetric marine worms. Although it is accepted as a phylum, the phylogenetic position of Sipuncula has been questionable. There is lack of molecular record on Sipuncula species while morphological data is not enough to distinguish the closer relationships between Annelida and Sipuncula. In order to add more data to genomic library of sipunculan species, Phascolosoma pacificum (Keferstein, 1866) was collected from seagrass area of Chuuk lagoon/Micronesia and its complete mitochondrial genome sequenced. Furthermore, phylogenetic relationship of the phylum Sipuncula and the other Trochozoan phyla investigate due to mitochondrial protein coding genes. Although there is lack of recorded data, our results support the idea that Sipuncula are nested within Annelida according to phylogenetic analyses of mitochondrial protein coding genes.

Edible peanut worm (Sipunculus nudus) in the Beibu Gulf: Resource, aquaculture, ecological impact and counterplan

Sipunculus nudus is an important economic species because of its high nutritional and medicinal values. The exploitation and utilization of S. nudus primarily occur in the coastal regions of the Beibu Gulf. However, wild resource of S. nudus is rapidly decreasing because of the overexploitation, which has led to considerable developments of artificial breeding techniques. The cultivation scale of S. nudus has increased in response to successful artificial breeding; however, methods for culturing S. nudus in tidal flats or ponds require further study. Most studies have focused on the breeding, nutrition, medical value and ecological impact of these worms. Studies on the distribution, sediment requirements, nutrition characteristics, breeding techniques and aquaculture ecology of this species are summarized in this paper to promote the development of the aquaculture industry for S. nudus. The high biomass of S. nudus in the Beibu Gulf is positively correlated with the sediment characteristics and water quality of the region. The production of peanut worm has improved to some extent through culturing; however, the nutrient value and ecological environment problems have been observed, which reflect the over exploitation of trace elements and the sediment. These problems will worsen unless they are resolved, and the release of organic materials, nitrogen and phosphorus during harvesting impacts the coastal environment. Moreover, genetic erosion is a potential risk for larvae in artificial breeding programs in tidal flats. Therefore, culturing and collecting methods should be improved and the wild resource conservation should be implemented to promote the sustainable development of the peanut worm.

Komposisi Kimia Cacing Kacang (Sipunculus nudus) di Kabupaten Raja Ampat dan Kabupaten Manokwari

Filum Sipuncula adalah biota laut unik, dari penampilan luarnya. Hewan ini mirip dengan cacing, sehingga diistilahkan peanut worm. Masyarakat pesisir Papua khususnya di Papua Barat telah memanfaatkan organisme ini sebagai bahan pangan, tetapi komposisi gizi dari spesies inu belum banyak dibahas. Penelitian dilakukan Maret-April 2014, bertujuan untuk mengetahui komposisi kimia dari Sipuncula nudus yang diambil dari perairan Raja Ampat dan Manokwari. Hasil menunjukkan bahwa kadar air S. nudus dari Kelurahan Sowi 4 Manokwari) yaitu 8.06%, kadar lemak tertinggi terdapat pada Kampung Amdui Raja Ampat) yaitu 1.70%, kadar protein tertinggi berasal dari Kampung Amdui Raja Ampat) yaitu 82.46%, karbohidrat tertinggi berasal dari Kelurahan Sowi 4 Manokwari) yaitu 7.26% dan kadar serat kasar Kelurahan Sowi 4 Manokwari) yaitu 1.05%. Sedangkan untuk kadar mineral besi dan kalsium tertinggi sampel dari Kampung Amdui Raja Ampat 11.07 Mg/100g dan kalsium sebesar 297.01Mg/100g. Sedangkan kadar mineral kalium tertinggi dari lokasi Kelurahan Sowi 4 Manokwari yaitu 207.48Mg/100g. Perbedaan ukuran panjang dan berat tidak memberikan pengaruh yang besar terhadap persentase kandungan gizi dan mineral dari Sipunculus nudus.

Recombinants from the crosses between amphidiploid and cultivated peanut (Arachis hypogaea) for pest-resistance breeding programs

Peanut is a major oilseed crop worldwide. In the Brazilian peanut production, silvering thrips and red necked peanut worm are the most threatening pests. Resistant varieties are considered an alternative to pest control. Many wild diploid Arachis species have shown resistance to these pests, and these can be used in peanut breeding by obtaining hybrid of A and B genomes and subsequent polyploidization with colchicine, resulting in an AABB amphidiploid. This amphidiploid can be crossed with cultivated peanut (AABB) to provide genes of interest to the cultivar. In this study, the sterile diploid hybrids from A. magna V 13751 and A. kempff-mercadoi V 13250 were treated with colchicine for polyploidization, and the amphidiploids were crossed with A. hypogaea cv. IAC OL 4 to initiate the introgression of the wild genes into the cultivated peanut. The confirmation of the hybridity of the progenies was obtained by: (1) reproductive characterization through viability of pollen, (2) molecular characterization using microsatellite markers and (3) morphological characterization using 61 morphological traits with principal component analysis. The diploid hybrid individual was polyploidized, generating the amphidiploid An 13 (A. magna V 13751 x A. kempff-mercadoi V 13250)4x. Four F1 hybrid plants were obtained from IAC OL 4 × An 13, and 51 F2 seeds were obtained from these F1 plants. Using reproductive, molecular and morphological characterizations, it was possible to distinguish hybrid plants from selfed plants. In the cross between A. hypogaea and the amphidiploid, as the two parents are polyploid, the hybrid progeny and selves had the viability of the pollen grains as high as the parents. This fact turns the use of reproductive characteristics impossible for discriminating, in this case, the hybrid individuals from selfing. The hybrids between A. hypogaea and An 13 will be used in breeding programs seeking pest resistance, being subjected to successive backcrosses until recovering all traits of interest of A. hypogaea, keeping the pest resistance.

A census of deep-water sipunculans (Sipuncula)

The Sipuncula, or peanut worms, are a small taxon of lophotrochozoan worms that live mostly in warm shallow waters, but little is known about the diversity and distribution of this group in the deeper parts of the ocean (>2000 m). To address this point, all existing information from the scientific literature on deep-water sipunculans was retrieved, and a census was organised in several data matrices by species and by geographic and bathymetric distribution. From this data, deep-water sipunculan fauna were found to include representatives of 4 families, 10 genera, 51 species and 3 subspecies. Geographical range maps for all the censused species were created. The most ubiquitous species are Nephasoma diaphanes (Gerould, 1913); Phascolion lutense Selenka, 1885; Golfingia muricaudata (Southern, 1913); Apionsoma murinae (Cutler, 1969), G. margaritacea (Sars, 1851) and Onchnesoma magnibathum Cutler, 1969. By contrast, 18 species of various genera in the dataset are considered to be extremely rare, with only one previous record. No endemic species have been detected on the sea bottoms investigated to date. With regard to vertical distribution, most deep-water sipunculans were collected at depths ranging from 2500 to 3000 m, whereas there were fewer ultra-abyssal and hadal records (>6500 m). This also applies to the deepest depths investigated (>7000 m), where only three isolated records of three different species (N. diaphanes, P. lutense and P. pacificum Murina, 1957) were found. By relating species richness to depth, a significant linear regression was found, with lower richness values at greater depths. Finally, attempts to relate the species richness values to latitudinal or longitudinal gradients have as yet proved unsuccessful. The conclusion drawn from this census is that sipunculan fauna down to a depth of 2000 m is characterised as remarkably sensitive to bathymetry, with the lowest species richness values recorded in the deeper bottoms.

Morphology, Biology, and Phylogenetic Position of the Bivalve Platomysia rugata (Heterodonta: Galeommatoidea), a Commensal with the Sipunculan Worm Sipunculus nudus.

The bivalve superfamily Galeommatoidea is characterized by its symbiotic associations with other marine invertebrates. However, for many galeommatoideans, the host species remains unknown. Platomysia (Galeommatoidea) is a monotypic genus including a single species P. rugata, which is distinguished from other galeommatoideans in having distinct and evenly spaced commarginal ribs on its shell surface. This species was described based on a single right valve shell collected in Nanao Bay, Japan Sea, by Habe in 1951 and has been known only from Japanese waters. However, the biology of living animals has never been reported. We found that this species lives in the burrows of the sipunculan worm Sipunculus nudus in mud flats in the Seto Inland Sea, Japan. We investigated its host association and described its shell morphology and anatomy. In addition, we performed a phylogenetic analysis using two nuclear (18S and 28S ribosomal RNA) genes to determine its phylogenetic position in Galeommatoidea. The result suggests that this species belongs to the clade of commensal bivalves together with Pseudopythina, Byssobornia, and Pergrinamor. Platomysia rugata and other two groups of sipunculan-associated galeommatoideans were not monophyletic, suggesting that association with sipunculans occurred at least three times in the galeommatoid evolution.

Genetic structure in two Phascolosoma species in the Pacific Ocean

ABSTRACTPhascolosoma agassizii, a commonly reported species of sipunculan worm, occurs at various depths throughout the north Pacific. However, previous studies have shown that this nominal species is actually comprised of two genetically divergent lineages. Phascolosoma agassizii is isolated to the eastern Pacific, whereas a second species, here referred to Phascolosoma sp., is located in the western Pacific and represents a unique, non-sister taxon to P. agassizii. Both species exhibit the same developmental mode with a long-lived, planktotrophic, pelagosphera larval stage, which may facilitate long-distance dispersal, although developmental timing differs. Using an inter-simple sequence repeat polymerase chain reaction (ISSR-PCR) genetic fingerprinting approach, this study examines non-coding polymorphic regions of the nuclear genomes of P. agassizii from four eastern Pacific populations and of Phascolosoma sp. from six western Pacific locations. Small-scale spatial genetic variation was analysed separately for each coastline using an Analysis of Molecular Variance. The data pointed to the potential presence of fine-scale genetic structure within P. agassizii, and recovered significant genetic structure within Phascolosoma sp. from the western Pacific. This study shows that ISSR-PCR is a relatively fast and cost-effective way to study fine-scale genetic diversity in marine invertebrates, although possible analyses and interpretations of the data are subject to the same limitations as other size polymorphism-based approaches.

A hermit crab living in association with a mobile scleractinian coral, Heteropsammia cochlea

Mobile free-living corals of the scleractinian genus Heteropsammia (Dendrophylliidae) are well known for their association with an endosymbiotic sipunculan worm (Yonge 1975; Hoeksema and Best 1991). This association is considered a mutualism, which allows them to inhabit soft substrata. It starts as the coral settles on a small gastropod shell that is already inhabited by the worm, after which it overgrows the shell and continues to provide shelter for the worm. The worm can protrude from its hole and pull the coral over the sediment, enabling it to migrate over the sediment (Goreau and Yonge 1968). Not much is known about the ecology of these mobile corals as most of their records are from greater depths and based on dry specimens (Hoeksema and Matthews 2015), but from an evolutionary perspective, it is clear that they show various traits that give them a unique position within their family (Arrigoni et al. 2014). On March 3, 2016, a living coral of Heteropsammia cochlea (Spengler, 1781) inhabited by a small hermit crab, Diogenes sp. (Diogenidae), was discovered on the sandy sea floor at 31 m depth in Ikomo Bay (28°05'46. N, 129°14'26. E), south of Kakeromajima Island, Kagoshima, southern Japan (Fig. 1). No sipunculan was found inside this coral (length 1.4 cm, width 1.2 cm, height 1.1 cm) in contrast to 17 other individuals of H. cochlea that were observed at the same site (5–30 m depth). This report represents the first observation of an association of a scleractinian coral with a hermit crab. Further surveys to understand the symbiotic relationships between mobile corals and their episymbionts are urgent as shallow habitats of free-living corals are mostly inside sheltered bays (e.g., Hoeksema and Best 1991; Cairns 2004; Hoeksema and Matthews 2015) and tend to be threatened by human activities, such as land reclamation and other disturbances causing runoff.