Association between Taxonomic Composition of Gut Microbiota and Host Single Nucleotide Polymorphisms in Crohn's Disease Patients from Russia.

Crohn's disease (CD) is a chronic relapsing inflammatory bowel disease of unknown etiology. Genetic predisposition and dysbiotic gut microbiota are important factors in the pathogenesis of CD. In this study, we analyzed the taxonomic composition of the gut microbiota and genotypes of 24 single nucleotide polymorphisms (SNP) associated with the risk of CD. The studied cohorts included 96 CD patients and 24 healthy volunteers from Russia. Statistically significant differences were found in the allele frequencies for 8 SNPs and taxonomic composition of the gut microbiota in CD patients compared with controls. In addition, two types of gut microbiota communities were identified in CD patients. The main distinguishing driver of bacterial families for the first community type are Bacteroidaceae and unclassified members of the Clostridiales order, and the second type is characterized by increased abundance of Streptococcaceae and Enterobacteriaceae. Differences in the allele frequencies of the rs9858542 (BSN), rs3816769 (STAT3), and rs1793004 (NELL1) were also found between groups of CD patients with different types of microbiota communities. These findings confirm the complex multifactorial nature of CD.

Adapting from Low to High: An Update to CO2-Concentrating Mechanisms of Cyanobacteria and Microalgae.

The intracellular accumulation of inorganic carbon (Ci) by microalgae and cyanobacteria under ambient atmospheric CO2 levels was first documented in the 80s of the 20th Century. Hence, a third variety of the CO2-concentrating mechanism (CCM), acting in aquatic photoautotrophs with the C3 photosynthetic pathway, was revealed in addition to the then-known schemes of CCM, functioning in CAM and C4 higher plants. Despite the low affinity of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) of microalgae and cyanobacteria for the CO2 substrate and low CO2/O2 specificity, CCM allows them to perform efficient CO2 fixation in the reductive pentose phosphate (RPP) cycle. CCM is based on the coordinated operation of strategically located carbonic anhydrases and CO2/HCO3- uptake systems. This cooperation enables the intracellular accumulation of HCO3-, which is then employed to generate a high concentration of CO2 molecules in the vicinity of Rubisco's active centers compensating up for the shortcomings of enzyme features. CCM functions as an add-on to the RPP cycle while also acting as an important regulatory link in the interaction of dark and light reactions of photosynthesis. This review summarizes recent advances in the study of CCM molecular and cellular organization in microalgae and cyanobacteria, as well as the fundamental principles of its functioning and regulation.

A leader peptide of the extracellular cyanobacterial carbonic anhydrase ensures the efficient secretion of recombinant proteins in Escherichia coli.

Several forms of EcaA protein, correspondent to the extracellular α-class carbonic anhydrase (CA) of cyanobacterium Crocosphaera subtropica ATCC 51142 were expressed in Escherichia coli. The recombinant proteins with no leader peptide (EcaA and its fusion with thioredoxin or glutathione S-transferase) were allocated inside cells in a full-length form; these cells did not display any extracellular CA activity. Soluble proteins (including that of periplasmic space) of E. coli cells that expressed both ЕсаА equipped with its native leader peptide (L-EcaA) as well as L-EcaA fused with thioredoxin or glutathione S-transferase at N-terminus, mainly contained the processed EcaA. The appearance of mature ЕсаА in outer layers of E. coli cells expressed leader peptide-containing forms of recombinant proteins, has been directly confirmed by immunofluorescent microscopy. Those cells also displayed high extracellular CA activity. In addition, the mature EcaA protein was detected in the culture medium. This suggests that cyanobacterial signal peptide is recognized by the secretory machinery and by the leader peptidase of E. coli even as a part of a fusion protein. The efficiency of EcaA leader peptide was comparable to that of PelB and TorA signal peptides, commonly used for biotechnological production of extracellular recombinant proteins in E. coli.

A new species of the Spirobranchuskraussii complex, S.akitsushima (Annelida, Polychaeta, Serpulidae), from the rocky intertidal zone of Japan.

A new species of Spirobranchus (Annelida: Serpulidae) is described based on specimens collected at the coastal Shonan area of Sagami Bay and the adjacent areas of Honshu, Japan. Spirobranchusakitsushima sp. nov. forms large aggregations in the intertidal rocky zone of warm-temperate Japanese shores. This species was referred to as Pomatoleioskraussii (Baird, 1864) until the monotypic genus Pomatoleios was synonymized with Spirobranchus. This new species is formally described based on morphologically distinct Japanese specimens with supporting DNA sequence data. The calcareous opercular endplate of Spirobranchusakitsushima sp. nov. lacks a distinct talon, but some specimens have a slight rounded swelling on the endplate underside, while in other species of the S.kraussii complex a talon is present, usually extended, and with bulges. We examined sub-fossil tube aggregations of the new species and suggest that such aggregation stranded ashore is a good indicator of vertical land movements (uplift and subsidence) resulting from past events, such as earthquakes, in Honshu, Japan.

Spirobranchus bakau sp. nov. from Singapore: yet another species of S. kraussii-complex (Polychaeta: Serpulidae).

The intertidal serpulid polychaete Spirobranchus kraussii was originally described from South Africa and has since been reported in numerous sub (tropical) localities around the world. Recently, however, S. kraussii was uncovered as a complex of morphologically similar and geographically restricted species, raising the need to revise S. cf. kraussii populations. We formally describe S. cf. kraussii from Singapore mangroves as Spirobranchus bakau sp. nov. based on morphological and molecular data. Despite their morphological similarities, Maximum Likelihood and Bayesian Inference analyses of 18S and Cyt b DNA sequence data confirm that S. bakau sp. nov. is genetically distinct from S. kraussii and other known species in the complex. Both analyses recovered S. bakau sp. nov. as part of a strongly supported clade (96% bootstrap, 1 posterior probability), comprising S. sinuspersicus, S. kraussii and S. cf. kraussii from Australia and Hawaii. Additionally, paratypes of S. kraussii var. manilensis, described from Manila Bay in the Philippines, were examined and elevated to the full species S. manilensis. Finally, we tested the hypothesis that fertilisation and embryonic development of S. bakau sp. nov. can occur under the wide range of salinities (19.630.9 psu) and temperatures (2531C) reported in the Johor Strait. Fertilisation success of ≥70% was achieved across a temperature range of 2532C and a salinity range of 2032 psu. Embryonic development, however, had a narrower salinity tolerance range of 2732 psu. Clarifying the taxonomic status of S. cf. kraussii populations reported from localities elsewhere in Singapore and Southeast Asia will be useful in establishing the geographical distribution of S. bakau sp. nov. and other members of the S. kraussii-complex.

Ecology and biogeography of the 'marine Geitlerinema' cluster and a description of Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov., Sodalinema stali sp. nov. and Baaleninema simplex gen. et sp. nov. (Oscillatoriales, Cyanobacteria).

Filamentous cyanobacteria belonging to the 'marine Geitlerinema' cluster are spread worldwide in saline environments and considered to play an important ecological role. However, the taxonomy of this group remains unclear. Here, we analyzed the phylogeny, ecology and biogeography of the 'marine Geitlerinema' cluster representatives and revealed two subclusters: (1) an 'oceanic' subcluster containing PCC7105 clade and black band disease (BBD) clade with free-living and pathogenic strains distributed in Atlantic, Indian and Pacific Ocean-related localities, and (2) a Sodalinema subcluster containing free-living strains from marine, hypersaline, saline-alkaline and soda lake habitats from the Eurasian and African continents. Polyphasic analysis using genetic and phenotypic criteria demonstrated that these two groups represent separate genera. Representatives of Sodalinema subcluster were phylogenetically attributed to the genus Sodalinema. Our data expand the ecological and geographical distribution of this genus. We emended the description of the genus Sodalinema and proposed three new species differing in phylogenetic, geographic and ecological criteria: Sodalinema orleanskyi sp. nov., Sodalinema gerasimenkoae sp. nov. and Sodalinema stali sp. nov. Additionally, a new genus and species Baaleninema simplex gen. et sp. nov. was discribed within the PCC7105 clade. By this, we put in order the current confusion of the 'marine Geitlerinema' group and highlight its ecological diversity.

Laminatubus (Serpulidae, Annelida) from eastern Pacific hydrothermal vents and methane seeps, with description of two new species.

The bathyal serpulid Laminatubus alvini ten Hove Zibrowius, 1986 was described from the periphery of hydrothermal vents of the Galapagos Rift and has been recorded from other vent communities of the East Pacific Rise (EPR). Here we assessed the biodiversity of serpulids collected from eastern Pacific hydrothermal vents and methane seeps using DNA sequences and morphology. Laminatubus alvini showed little genetic variation over a wide geographic range from the Alarcon Rise vents in southern Gulf of California (~23°N), to at least a point at 38°S on the EPR. Specimens from several methane seeps off Costa Rica and the Gulf of California (Mexico) differed markedly from those of Laminatubus alvini on DNA sequence data and in having seven thoracic chaetigers and lacking Spirobranchus-type special collar chaetae, thus fitting the diagnosis of Neovermilia. However, phylogenetic analysis of molecular data showed that L. alvini and the seep specimens form a well-supported clade. Moreover, among the seep specimens there was minimally a ~7% distance in mitochondrial cytochrome b sequences between a shallow-water (1000 m) seep clade restricted to Costa Rica and a deep-water clade (1800 m) from Costa Rica to Gulf of California. We describe the seep taxa here as morphologically indistinguishable L. paulbrooksi n. sp. and L. joycebrooksae n. sp.

Annelids of the eastern Australian abyss collected by the 2017 RV 'Investigator' voyage.

In Australia, the deep-water (bathyal and abyssal) benthic invertebrate fauna is poorly known in comparison with that of shallow (subtidal and shelf) habitats. Benthic fauna from the deep eastern Australian margin was sampled systematically for the first time during 2017 RV 'Investigator' voyage 'Sampling the Abyss'. Box core, Brenke sledge, and beam trawl samples were collected at one-degree intervals from Tasmania, 42°S, to southern Queensland, 24°S, from 900 to 4800 m depth. Annelids collected were identified by taxonomic experts on individual families around the world. A complete list of all identified species is presented, accompanied with brief morphological diagnoses, taxonomic remarks, and colour images. A total of more than 6000 annelid specimens consisting of 50 families (47 Polychaeta, one Echiura, two Sipuncula) and 214 species were recovered. Twenty-seven species were given valid names, 45 were assigned the qualifier cf., 87 the qualifier sp., and 55 species were considered new to science. Geographical ranges of 16 morphospecies extended along the eastern Australian margin to the Great Australian Bight, South Australia; however, these ranges need to be confirmed with genetic data. This work providing critical baseline biodiversity data on an important group of benthic invertebrates from a virtually unknown region of the world's ocean will act as a springboard for future taxonomic and biogeographic studies in the area.

Mitochondrial genome of Sabella spallanzanii (Gmelin, 1791) (Sabellida: Sabellidae).

We report the mitochondrial genome of Sabella spallanzanii, an invasive Mediterranean sabellid introduced to Australia and New Zealand. The mitogenome is 15,581 bp long and consists of 38 genes, including 13 protein coding genes, two rRNA genes, and 23 tRNA genes. It shows deviations from the putative annelid ground pattern, such as gene order re-arrangements and regions encoding on the negative strand. It is, however, very different from the mitogenome of the closely related serpulid, Spirobranchus giganteus. Phylogenetic analyses of the mitochondrial genes support a sister relationship of Sabella spallanzanii and Spirobranchus giganteus.

Another blow to the conserved gene order in Annelida: Evidence from mitochondrial genomes of the calcareous tubeworm genus Hydroides.

Mitochondrial genomes are frequently applied in phylogenetic and evolutionary studies across metazoans, yet they are still poorly represented in many groups of invertebrates, including annelids. Here, we report ten mitochondrial genomes from the annelid genus Hydroides (Serpulidae) and compare them with all available annelid mitogenomes. We detected all 13 protein coding genes in Hydroides spp., including the atp8 which was reported as a missing gene in the Christmas Tree worm Spirobranchus giganteus, another annelid of the family Serpulidae. All available mitochondrial genomes of Hydroides show a highly positive GC skew combined with a highly negative AT skew - a feature consistent with that found only in the mitogenome of S. giganteus. In addition, amino acid sequences of the 13 protein-coding genes showed a high genetic distance between the Hydroides clade and S. giganteus, suggesting a fast rate of mitochondrial sequence evolution in Serpulidae. The gene order of protein-coding genes within Hydroides exhibited extensive rearrangements at species level, and were different from the arrangement patterns of other annelids, including S. giganteus. Phylogenetic analyses based on protein-coding genes recovered Hydroides as a monophyletic group sister to Spirobranchus with a long branch, and sister to the fan worm Sabellidae. Yet the Serpulidae + Sabellidae clade was unexpectedly grouped with Sipuncula, suggesting that mitochondrial genomes alone are insufficient to resolve the phylogenetic position of Serpulidae within Annelida due to its high base substitution rates. Overall, our study revealed a high variability in the gene order arrangement of mitochondrial genomes within Serpulidae, provided evidence to question the conserved pattern of the mitochondrial gene order in Annelida and called for caution when applying mitochondrial genes to infer their phylogenetic relationships.

Alcohol stress on cyanobacterial membranes: New insights revealed by transcriptomics.

Cyanobacteria are model photosynthetic prokaryotic organisms often used in biotechnology to produce biofuels including alcohols. The effect of alcohols on cyanobacterial cell physiology and specifically on membrane fluidity is poorly understood. Previous research on various primary aliphatic alcohols found that alcohols with a short hydrocarbon chain (C1-C3) do not affect expression of genes related to membrane physical state. In addition, less water-soluble alcohols with a hydrocarbon chain longer than C8 are found to have a reduced ability to reach cellular membranes hence do not drastically change membrane physical state or induce expression of stress-responsive genes. Therefore, hexan-1-ol (C6) is suggested to have the most profound effect on cyanobacterial membrane physical state. Here, we studied the effects of hexan-1-ol on the cyanobacterium Synechocystis sp. PCC 6803 transcriptome. The transcriptome data obtained is compared to the previously reported analysis of gene expression induced by benzyl alcohol and butan-1-ol. The set of genes whose expression is induced after exposure to all three studied alcohols is identified. The expression under alcohol stress for several general stress response operons is analyzed, and examples of antisense interactions of RNA are investigated.

Two new species of Sabellariidae (Annelida, Polychaeta) from the abyss of eastern Australia.

In May-June 2017 an expedition on board RV 'Investigator' sampled benthic communities along the lower slope and abyss of eastern Australia from off Tasmania to the Coral Sea. Over 200 sabellariid specimens of the genera Phalacrostemma and Gesaia were collected during the voyage and deposited in the Australian Museum. Here we describe two new species Gesaia csiro n. sp. (4414-4436 m) and Phalacrostemma timoharai n. sp. (1013-1093 m). We did not formally describe another species of Phalacrostemma due to poor condition of the single specimen. Gesaia csiro n. sp. is the first record of the genus from Australian waters (only a planktonic larva attributed to the genus has previously been recorded), and it can be distinguished from other congeners by the smooth surface of inner paleae, distal thecae of outer paleae with long, irregular and expanded distal fringe and circled distal margin. Phalacrostemma timoharai n. sp. differs from congeners by the following combination of characters: presence of the buccal flap, absence of tentacular filament, 18-22 pairs of outer paleae, two pairs of neuropodial cirri on first thoracic segment, and only one pair of lateral lobes on second thoracic segment. Morphological descriptions are accompanied by mitochondrial cytochrome c oxidase subunit 1 (COI) and ribosomal (16S, 18S and 28S) sequence data. A key to all Australian species of sabellariids is given.

A new species of the Spirobranchus kraussii-complex (Annelida, Serpulidae) from the Persian Gulf and Gulf of Oman.

A recent study (Simon et al. 2019) confirmed that Spirobranchus kraussii is neither a widely distributed tropical species of Indo-Pacific origin nor a Lessepsian migrant to the Mediterranean, but a large complex of species, some of which might be indeed invasive. Thus, a common intertidal gregarious serpulid, previously attributed to S. kraussii in the Persian Gulf and Gulf of Oman, is described herein as Spirobranchus sinuspersicus sp. nov., using a combination of morphological and molecular data. The new species differs from S. kraussii by smaller size, fewer abdominal chaetigers, arrangement of abdominal chaetae and shape of opercular endplate talon. Results of phylogenetic analyses of a dataset combining 18S nucleotide and Cyt-b amino-acid sequences of S. sinuspersicus sp. nov. and Spirobranchus spp. available from GenBank supported monophyly of S. kraussii complex (including S. cariniferus) nested within Spirobranchus and thus, provided molecular support for synonymy of Pomatoleios with Spirobranchus proposed based on morphological criteria. The new species forms a well-supported clade with (S. kraussii (sp. 2 Hawaii + sp. 3 Australia)) clade, which in turn forms a clade with Spirobranchus sp.1 from temperate Japan, while S. cariniferus from New Zealand forms a basal grade. Evidence of substitution saturation of Cyt-b nucleotide sequences suggests that using translated amino-acid sequences to exclude non-informative substitutions should provide a better phylogenetic resolution for the genus Spirobranchus. Further studies are required to determine the invasive status of S. sinuspersicus sp. nov. as well as taxonomic and invasive status of S. cf. kraussii populations from the Mediterranean Sea, Suez Bay, Pakistan, India, Sri Lanka, Philippines, Singapore, and Panama.

A new species of the sanguinea-group Quatrefages, 1866 (Annelida: Eunicidae: Marphysa) from the Philippines.

A new species of the Marphysa sanguinea group, M. iloiloensis n. sp. (Annelida: Eunicida: Eunicidae), is described from the Marine Annelids Hatchery of the Southeast Asian Fisheries Development Center, Aquaculture Department (SEAFDEC- AQD), Iloilo Province, Philippines. It represents the first record of this group in the Philippines. The new species is most similar morphologically to M. hongkongensa Wang, Zhang Qiu, 2018, but can be distinguished from it by having fewer branchial filaments, a pair of faint eyes (absent in M. hongkongensa), and in slight differences in jaw morphology and chaetation. The embryos of the new species develop inside a jelly cocoon attached to the entrance of the adult burrow; this is the first time that egg-containing cocoons have been found in any species of the sanguinea-group. Phylogenetic analysis based on the mitochondrial gene cytochrome c oxidase subunit I (COI) revealed that Marphysa iloiloensis n. sp. is genetically distinct from all other analysed Marphysa species and forms a sister group to M. hongkongensa. A revised identification key to members of the sanguinea-group in Southeast Asia is provided.

A revision of the genus Petta Malmgren, 1866 (Annelida: Pectinariidae), with two new species from deep waters of southeastern Australia, and comments on phylogeny of the family.

Petta Malmgren, 1866 is a small and poorly known genus of the annelid family Pectinariidae Quatrefages, 1866. Prior to this study, the genus comprised four species P. pusilla Malmgren, 1866 (type locality Gullmarsfjord, west coast of Sweden), P. assimilis McIntosh, 1885 (type locality between Prince Edward and Kerguelen Island, southern Indian Ocean), P. pellucida (Ehlers, 1887) (type locality Santarem Channel between Cay Sal Bank and Bahamas, Caribbean Sea) and P. tenuis Caullery, 1944 (type locality Sulu, Philippines, tropical Pacific Ocean), the two last ones were known only from the original description. We revised the genus by re-examining the types and providing updated illustrated re-descriptions of its species, except for P. assimilis of which the type material has been lost. Commonly used morphological characters of the genus are expanded to also include new ones such as the presence of pair of lateral ear-shaped lobes adjacent to dorsal base of cephalic veil, pair of ventral lappets on segment 1, pair of dorso-lateral pads on segment 5, large basal hump on branchiae, and a rounded anterior peg with a blunt tip and a longitudinal row of two major teeth on uncini. The type species P. pusilla is recognised as having four lappets on the anterior margins of cephalic veil and a large lower lip posterior to buccal cavity. Two species P. investigatoris n. sp. and P. williamsonae n. sp. are described from deep water off the coast of southeastern Australia and represent the first records of this genus in Australian waters. A phylogenetic position of one new species was assessed in the framework of a phylogeny based on a fragment of the mitochondrial cytochrome oxidase I gene (mtCOI). An updated taxonomic key to Pectinariidae genera and all species of Petta is given.

Draft Genome Sequences of a Putative Prokaryotic Consortium (IPPAS B-1204) Consisting of a Cyanobacterium (Leptolyngbya sp.) and an Alphaproteobacterium (Porphyrobacter sp.).

A new presumably simple consortium of a Leptolyngbya sp. and a Porphyrobacter sp. was isolated from Tolbo Lake in Mongolia. The draft genome sequences of both species are reported. The consortium has been deposited in the Collection of Microalgae and Cyanobacteria of the Institute of Plant Physiology, Moscow, Russia, under the accession number IPPAS B-1204.

Highly active extracellular α-class carbonic anhydrase of Cyanothece sp. ATCC 51142.

Here, for the first time, we report the presence of highly active extracellular carbonic anhydrase (CA) of α-class in cyanobacterial cells. The enzyme activity was confirmed both in vivo in intact cells and in vitro, using the recombinant protein. CA activity in intact cells of Cyanothece sp. ATCC 51142 reached ∼0.6 Wilbur-Anderson units (WAU) per 1 mg of total cell protein, and it was inhibited by a specific CAs inhibitor, ethoxyzolamide. The genes cce_4328 (ecaA) and cce_0871 (ecaB), encoding two potential extracellular CAs of Cyanothece have been cloned, and the corresponding proteins EcaA and EcaB, representing CAs of α- and ß-class, respectively, have been heterologously expressed in Escherichia coli. High specific activity (∼1.1 × 104 WAU per 1 mg of target protein) was detected for the recombinant EcaA only. The presence of EcaA in the outer cellular layers of Cyanothece was confirmed by immunological analysis with antibodies raised against the recombinant protein. The absence of redox regulation of EcaA activity indicates that this protein does not possess a disulfide bond essential for some α-class CAs. The content and activity of EcaA in a fraction of periplasmic proteins was higher in Cyanothece cells grown at ambient concentration of CO2 (0.04%) compared to those grown at an elevated CO2 concentration (1.7%). At the same time, the level of ecaA gene mRNA varied insignificantly in response to changes in CO2 supply. Our results indicate that EcaA is responsible for CA activity of intact Cyanothece cells and point to its possible physiological role under low-CO2 conditions.

Developmental studies provide new insights into the evolution of sense organs in Sabellariidae (Annelida).

BACKGROUND: Sabellarids, also known as honeycomb or sandcastle worms, when building their tubes, produce chemical signals (free fatty acids) that are responsible for larval settlement and the formation of three-dimensional aggregations. The larval palps and the dorsal hump (becoming the median organ in adults) are presumed to participate in such a substrate selection during settlement. Notably, the sabellariid median organ is an apparently unique organ among annelids that has been attributed with a sensory function and perhaps with some affinities to the nuchal organs of other polychaetes. Nevertheless, detailed investigations of this prominent character complex including ultrastructural examinations are lacking so far. RESULTS: Our comprehensive investigations provide data about the anterior sensory organs in Sabellariidae and inform about their transformation during pelagic larval development. We used a comparative approach including immunostaining with subsequent confocal laser scanning microscopy (clsm), histological sections as well as electron microscopy in a range of larval and adult stages of two sabellariid species. We find that the neuronal innervation as well as the ultrastructure of the sabellariid ciliary structures along the median organ are highly comparable with that of nuchal organs known from other polychaetes. Furthermore, the myoinhibitory protein (MIP) - a protein known to be also involved into chemo-sensation - was detected in the region of the larval median organ. Moreover, we reveal the presence of an unusual type of photoreceptor as part of the median organ in Idanthyrsus australiensis with a corrugated sensory membrane ultrastructure unlike those observed in the segmental ocelli of other polychaetes. CONCLUSIONS: We are describing for the first time the nuchal organ-like structures in different developmental stages of two species of Sabellariidae. The external morphology, neuronal innervation, developmental fate and ultrastructure of the newly-discovered median organ-based ciliary pits are comparable with the characteristics known for annelid nuchal organs and therefore indicate a homology of both sensory complexes. The presence of myoinhibitory peptide (MIP) in the respective region supports such a hypothesis and exhibits the possibility of an involvement of the entire sabellariid median organ complex, and in particular the prominent ciliated pits, in chemo-sensation.

Barcoding and multi-locus phylogeography of the globally distributed calcareous tubeworm genus Hydroides Gunnerus, 1768 (Annelida, Polychaeta, Serpulidae).

Hydroides is a large and diverse group of calcareous tubeworms (Serpulidae, Annelida) recognised by a distinctive but variable two-tiered operculum. Despite considerable research using several species of Hydroides as models in ecological and biofouling studies, phylogenetic and biogeographic relationships within the genus are still poorly understood. Using combined mitochondrial (COI, cytochrome b) and nuclear (18S, 28S and ITS) gene markers for 284 individuals of 45 morphospecies of Hydroides, we investigated the global phylogenetic and biogeographic relationships within the genus. Phylogenetic topologies were well supported and indicated high genetic diversity within Hydroides, revealing potential cryptic species. Present results also include the first COI barcoding data enabling rapid and effective species identification of Hydroides on a global scale. Phylogenetic relationships within Hydroides were more concordant with geographical distributions than morphological similarity of their opercula. Molecular divergence estimates suggested the origin and subsequent diversification in the western Tethys Sea followed by a shift of the historical centre of diversity from the Indo-Mediterranean region to the central Indo-Pacific during the last 50 million years. Further studies on population genetics of species consisting of multiple lineages would provide a better understanding on the status of potential cryptic species. Furthermore, paleogeographic studies based on fossil Hydroides tubes would provide evidence to test this biogeographic hypothesis.