Pharmaceutical Residues in Edible Oysters along the Coasts of the East and South China Seas and Associated Health Risks to Humans and Wildlife.

The investigation of pharmaceuticals as emerging contaminants in marine biota has been insufficient. In this study, we examined the presence of 51 pharmaceuticals in edible oysters along the coasts of the East and South China Seas. Only nine pharmaceuticals were detected. The mean concentrations of all measured pharmaceuticals in oysters per site ranged from 0.804 to 15.1 ng g-1 of dry weight, with antihistamines being the most common. Brompheniramine and promethazine were identified in biota samples for the first time. Although no significant health risks to humans were identified through consumption of oysters, 100-1000 times higher health risks were observed for wildlife like water birds, seasnails, and starfishes. Specifically, sea snails that primarily feed on oysters were found to be at risk of exposure to ciprofloxacin, brompheniramine, and promethazine. These high risks could be attributed to the monotonous diet habits and relatively limited food sources of these organisms. Furthermore, taking chirality into consideration, chlorpheniramine in the oysters was enriched by the S-enantiomer, with a relative potency 1.1-1.3 times higher when chlorpheniramine was considered as a racemate. Overall, this study highlights the prevalence of antihistamines in seafood and underscores the importance of studying enantioselectivities of pharmaceuticals in health risk assessments.

Histology and transcriptomic analyses of barnacles with different base materials and habitats shed lights on the duplication and chemical diversification of barnacle cement proteins.

BACKGROUND: Barnacles are sessile crustaceans that attach to underwater surfaces using barnacle cement proteins. Barnacles have a calcareous or chitinous membranous base, and their substratum varies from biotic (e.g. corals/sponges) to abiotic surfaces. In this study, we tested the hypothesis that the cement protein (CP) composition and chemical properties of different species vary according to the attachment substrate and/or the basal structure. We examined the histological structure of cement glands and explored the variations in cement protein homologs of 12 barnacle species with different attachment habitats and base materials. RESULTS: Cement gland cells in the rocky shore barnacles Tetraclita japonica formosana and Amphibalanus amphitrite are eosinophilic, while others are basophilic. Transcriptome analyses recovered CP homologs from all species except the scleractinian coral barnacle Galkinia sp. A phylogenomic analysis based on sequences of CP homologs did not reflect a clear phylogenetic pattern in attachment substrates. In some species, certain CPs have a remarkable number of paralogous sequences, suggesting that major duplication events occurred in CP genes. The examined CPs across taxa show consistent bias toward particular sets of amino acid. However, the predicted isoelectric point (pI) and hydropathy are highly divergent. In some species, conserved regions are highly repetitive. CONCLUSIONS: Instead of developing specific cement proteins for different attachment substrata, barnacles attached to different substrata rely on a highly duplicated cementation genetic toolkit to generate paralogous CP sequences with diverse chemical and biochemical properties. This general CP cocktail might be the key genetic feature enabling barnacles to adapt to a wide variety of substrata.

Sponge symbiosis is facilitated by adaptive evolution of larval sensory and attachment structures in barnacles.

Symbiotic relations and range of host usage are prominent in coral reefs and crucial to the stability of such systems. In order to explain how symbiotic relations are established and evolve, we used sponge-associated barnacles to ask three questions. (1) Does larval settlement on sponge hosts require novel adaptations facilitating symbiosis? (2) How do larvae settle and start life on their hosts? (3) How has this remarkable symbiotic lifestyle involving many barnacle species evolved? We found that the larvae (cyprids) of sponge-associated barnacles show a remarkably high level of interspecific variation compared with other barnacles. We document that variation in larval attachment devices are specifically related to properties of the surface on which they attach and metamorphose. Mapping of the larval and sponge surface features onto a molecular-based phylogeny showed that sponge symbiosis evolved separately at least three times within barnacles, with the same adaptive features being found in all larvae irrespective of phylogenetic relatedness. Furthermore, the metamorphosis of two species proceeded very differently, with one species remaining superficially on the host and developing a set of white calcareous structures, the other embedding itself into the live host tissue almost immediately after settlement. We argue that such a high degree of evolutionary flexibility of barnacle larvae played an important role in the successful evolution of complex symbiotic relationships in both coral reefs and other marine systems.

Effects of polystyrene microplastics on larval development, settlement, and metamorphosis of the intertidal barnacle Amphibalanus amphitrite.

The effects of microplastic on mortality and sublethal responses on larval development of meroplankton are still largely unknown. Present study investigated the effects of four sizes of virgin spherical polystyrene microplastics (diameter 1.7, 6.8, 10.4, 19.0 µm) on naupliar (stage II-VI) and cypris larvae of barnacle Amphibalanus amphitrite at environmentally relevant concentrations (1, 10, 100, 1000 beads mL-1). Essential life-history traits, including mortality, development time and rates of growth, settling, and metamorphosis were measured throughout the entire larval development. Feeding experiments were conducted to evaluate if microplastics decreased naupliar feeding due to physical impacts or selective feeding of nauplii. The results showed that A. amphitrite stage II nauplii were able to ingest and efficiently egest all sizes of microplastics. All the life-history endpoints measured were not significantly affected by all sizes of microplastics at any concentration tested. Presence of all sizes of microplastics did not cause physical interference on naupliar feeding and all stages of nauplius larvae (stage III-VI) did not selectively feed on microplastics. However, the feeding ability of stage III nauplius appeared to be affected by 1.7 µm at 1000 beads mL-1 which was possibly due to individual variations rather than microplastics' impacts. Overall, the full larval development of barnacle A. amphitrite was not affected by microplastics at environmentally relevant concentrations under laboratory condition.

Mitochondrial genome of Tesseropora rosea: molecular evidence for non-monophyly of the genus Tetraclita.

The complete mitochondrial genome of Tesseropora rosea (Tetraclitidae) was presented. The genome is a circular molecule of 15,330 bp, which encodes 13 PCGs, two rRNA genes, and 22 tRNA genes. The length of all non-coding regions is 768 bp, with the longest one speculated as the control region (255 bp), which is located between 12S rRNA and trnK. Phylogenetic analysis based on mitochondrial PCGs shows that T. rosea is nested within the genus Tetraclita, more closely related to Tetraclita japonica than to Tetraclita rufotincta or Tetraclita serrata. Thus, the monophyly of the genus Tetraclita is not supported.

Description of five new coral associated Barnacles of the genus Trevathana (Balanomorpha: Pyrgomatidae) in Pacific Waters.

Five new species of coral inhabiting barnacles of the genus Trevathana (Balanomorpha: Pyrgomatidae), T. dongshaensis sp. nov., T. conica sp. nov., T. doni sp. nov., T. longidonta sp. nov. and T. taiwanus sp. nov., are described. These species are found in West Pacific waters including Japan, Taiwan (mainland and adjacent outlying islands including Dongsha Atoll) and Papua New Guinea. The species exhibit morphological differences in the scutum, the tergum, and cirri II and III, and form distinct clades in a phylogenetic tree based on DNA sequences of two genes, 12S rDNA and cytochrome C oxidase subunit I. Three of the five species, T. dongshaensis sp. nov., T. conica sp. nov. and T. taiwanus sp. nov., have relatively narrow distribution ranges and were recorded from the Dongsha Atoll (T. dongshaensis sp. nov. and T. conica sp. nov.) and the Taiwanese mainland (T. taiwanus sp. nov.). Trevathana longidonta sp. nov. and T. doni sp. nov. have wider distributions. Trevathana longidonta sp. nov. was collected from Japan, Taiwan and Dongsha Atoll and T. doni sp. nov. was collected from Taiwan, Dongsha Atoll and Papua New Guinea. In the waters of Japan, Taiwan and Dongsha Atoll, all the recorded Trevathana species inhabit corals of the family Merulinidae. However, in Papua New Guinea, T. doni sp. nov. is also recorded in the coral Oxypora, belonging to the family Lobophylliidae, and individuals living on Lobophyllidae and Merulinidae did not exhibit great variation in the divergence of the COI and 12S genes.

A unique duplication of gene cluster (S2-C-Y) in Epopella plicata (Crustacea) mitochondrial genome and phylogeny within Cirripedia.

Barnacles (Crustacea: Cirripedia) are important model species in invertebrate larval biology, intertidal ecology, and anti-fouling researches. The complete mitochondrial genome of the intertidal barnacle Epopella plicata Gray, 1843 (Cirripedia: Sessilia: Tetraclitidae) is presented. The mitochondrial genome of E. plicata of 15 296 bp in length encodes 13 PCGs, 2 rRNA genes, and 25 tRNA genes. The genome of E. plicata has a duplicate gene cluster (trnS2-trnC-trnY) that is unique in the infraclass Cirripedia. The two copies of trnC share identical sequences, but nucleotide substitutions are observed in the other two pairs of tRNAs. Comparison of the two trnS2 indicates that DHU arm and acceptor stem have nucleotide variation. In the two trnY, nucleotide variations are found in the acceptor stem, TψC arm, DHU arm, and variable loop. However, there is no nucleotide variation in the anticodon arm of the three tRNAs. Epopella plicata mitochondrial genome shares seven gene rearrangements with that of Tetraclita japonica (Tetraclitidae), including trnK, trnA, trnE/trnS1, trnP/trnT, trnI/trnQ, trnY and trnC. Comparison of gene orders in the two tetraclitid barnacles and the pancrustacean ground pattern suggests that the arrangement of E. plicata mitochondrial genome is a derived character in this species within the family Tetraclitidae. Sequence analysis of all available barnacle mitochondrial genomes shows that within the order Sessilia, E. plicata and Tetraclita japonica cluster together, resulting in monophyly of Tetraclitidae. Notochthamalus scabrosus (Chthamalidae) is at the basal position of the order Sessilia. Monophyly of the family Balanidae was questioned based on both gene order comparison and sequence analyses, and its phylogenetic status needs to be elucidated further.

Mitochondrial genome of the acorn barnacle Tetraclita rufotincta Pilsbry, 1916: highly conserved gene order in Tetraclitidae.

The complete mitochondrial genome of the intertidal barnacle Tetraclita rufotincta Pilsbry, 1916 (Crustacea: Maxillopoda: Sessilia) is presented. The genome is a circular molecule of 15,236 bp, which encodes a set of 37 typical metazoan mitochondrial genes. All non-coding regions are 438 bp in length, with the longest one speculated as the control region (242 bp), which is located between srRNA and trnK. Comparison of the genome and those of three other species from Tetraclitidae shows that gene arrangement is identical, indicating that the mitochondrial gene order is highly conserved in the family. Moreover, in comparison with the pancrustacean ground pattern, the four species of Tetraclitidae share three large conserved gene blocks. Phylogenetic analysis based on 13 mitochondrial PCGs shows that Chelonbia testudinaria (Coronulidae) clusters with the four species of Tetraclitidae. Within Tetraclitidae, T. serrata clusters with T. japonica, and the two grouped with T. rufotincta with high support (BP = 100), with T. divisa as the most distantly related species (BP = 100).

Galkinius Perreault, 2014 or Darwiniella (Anderson, 1992)? A new coral-associated barnacle sharing characteristics of these two genera in Pacific waters (Crustacea, Cirripedia, Thoracica, Pyrgomatidae).

A new species of coral associated barnacle (Balanomorpha: Pyrgomatidae) sharing morphological features of Darwiniella (Anderson, 1992) and Galkinius Perreault, 2014 is described. It has a fused shell and opercular plates, characteristic of Darwiniella. However, the morphology of the tergum and somatic body are closer to Galkinius. Sequence divergence of mitochondrial DNA 12S rDNA and COI reveals this new species clusters with the Galkinius clade. Therefore this new form is assigned to the genus Galkinius, as G. maculosussp. n. Concomitantly the diagnosis of Galkinius is emended to include species with fused or four- plated shells and fused opercular plates. The new species is distinct from all Galkinius species in having a fused shell. It inhabits the corals Lobophyllia spp. and is distributed from the Dongsha Atoll in the South China Sea, Orchid Island of Taiwan in the Pacific Ocean, to Madang in Papua New Guinea waters.

Community Structure of Macrobiota and Environmental Parameters in Shallow Water Hydrothermal Vents off Kueishan Island, Taiwan.

Hydrothermal vents represent a unique habitat in the marine ecosystem characterized with high water temperature and toxic acidic chemistry. Vents are distributed at depths ranging from a few meters to several thousand meters. The biological communities of shallow-water vents have, however, been insufficiently studied in most biogeographic areas. We attempted to characterize the macrofauna and macroflora community inhabiting the shallow-water vents off Kueishan Island, Taiwan, to identify the main abiotic factors shaping the community structure and the species distribution. We determined that positively buoyant vent fluid exhibits a more pronounced negative impact to species on the surface water than on the bottom layer. Species richness increased with horizontal distance from the vent, and continuing for a distance of 2000 m, indicating that the vent fluid may exert a negative impact over several kilometers. The community structure off Kueishan Island displayed numerous transitions along the horizontal gradient, which were broadly congruent with changes in environmental conditions. Combination of variation in Ca2+, Cl-, temperature, pH and depth were revealed to show the strongest correlation with the change in benthic community structure, suggesting multiple factors of vent fluid were influencing the associated fauna. Only the vent crabs of Kueishan Island may have an obligated relationship with vents and inhabit the vent mouths because other fauna found nearby are opportunistic taxa that are more tolerant to acidic and toxic environments.

The complete mitochondrial genome of the fire coral-inhabiting barnacle Megabalanus ajax (Sessilia: Balanidae): gene rearrangements and atypical gene content.

The complete mitochondrial genome of Megabalanus ajax Darwin, 1854 (Sessilia: Balanidae) is reported. Compared to typical gene content of metazoan mitochondrial genomes, duplication of one tRNA gene (trnL2) and absence of another tRNA gene (trnS1) are identified in M. ajax mitochondrial genome. There is a replacement of one tRNA (trnS1) by another tRNA (trnL2) in M. ajax mitochondrial genome compared to Megabalanus volcano mitochondrial genome. Inversion of a six-gene block (trnP-nd4L-nd4-trnH-nd5-trnF) is found between M. ajax/M. volcano and Tetraclita japonica mitochondrial genomes. With reference to the pancrustacean mitochondrial ground pattern, there is an inversion of a large gene block from the light strand to heavy strand in the two Megabalanus mitochondrial genomes, including three PCGs and two tRNAs (nd4L-nd4-trnH-nd5-trnF). Furthermore, four tRNAs (trnA, trnE, trnQ and trnC) exhibit translocation, while translocation and inversion occur in three tRNAs (trnP, trnY and trnK).

The mitochondrial genome of Nobia grandis Sowerby, 1839 (Cirripedia: Sessilia): the first report from the coral-inhabiting barnacles family Pyrgomatidae.

This work presents the coral-inhabiting barnacle Nobia grandis Sowerby, 1839 complete mitochondrial genome, which is the first report from the family Pyrgomatidae (Cirripedia: Sessilia). The N. grandis mitochondrial genome is 15,032 bp in length, containing a total of 469 bp of non-coding nucleotides spreading in 11 intergenic regions (with the largest region of 376 bp). Compared with the pancrustacean ground pattern, there are not less than seven tRNAs rearranged in the N. grandis mitochondrial genome. Gene overlaps are founded in eight places. Nine PCGs (COX1-3, ATP6, ATP8, CYTB, ND2, ND3 and ND6) are encoded on the heavy strand while the remaining 4 PCGs and the two rRNAs are located on the light strand. As the first representative from the family Pyrgomatidae, the N. grandis mitochondrial genome will help us to explore the evolutionary history and molecular evolution of coral barnacles and Sessilia in future studies.

Mitochondrial genome of the intertidal acorn barnacle Tetraclita serrata Darwin, 1854 (Crustacea: Sessilia): Gene order comparison and phylogenetic consideration within Sessilia.

The complete mitochondrial genome of the intertidal barnacle Tetraclita serrata Darwin, 1854 (Crustacea: Maxillopoda: Sessilia) is presented. The genome is a circular molecule of 15,200 bp, which encodes 13 PCGs, 2 ribosomal RNA genes, and 22 transfer RNA genes. All non-coding regions are 591 bp in length, with the longest one speculated as the control region (389 bp), which is located between srRNA and trnK. The overall A+T content of the mitochondrial genome of T. serrata is 65.4%, which is lowest among all the eight mitochondrial genomes reported from sessile barnacles. There are variations of initiation and stop codons in the reported sessile barnacle mitochondrial genomes. Large-scale gene rearrangements are found in these genomes as compared to the pancrustacean ground pattern. ML and Bayesian analyses of all 15 complete mitochondrial genomes available from Maxillopoda lead to identical phylogenies. The phylogenetic tree based on mitochondrial PCGs shows that Argulus americanus (Branchiura) cluster with Armillifer armillatus (Pentastomida), distinct from all ten species from Cirripedia. Within the order Sessilia, Amphibalanus amphitrite (Balanidae) clusters with Striatobalanus amaryllis (Archaeobalanidae), and Nobia grandis (Pyrgomatidae). However, the two Megabalanus (Balanidae) are separated from the above grouping, resulting in non-monophyly of the family Balanidae. Moreover, the two Megabalanus have large-scale rearrangements as compared to the gene order shared by former three species. Therefore, both phylogenetic analysis using PCG sequences and gene order comparison suggest that Balanidae is not a monophyletic group. Given the limited taxa and moderate support values of the internal branches, the non-monophyly of the family Balanidae requires further verification.

Molecular phylogeny of the acorn barnacle family Tetraclitidae (Cirripedia: Balanomorpha: Tetraclitoidea): validity of shell morphology and arthropodal characteristics in the systematics of Tetraclitid barnacles.

Shell structure is a crucial aspect of barnacle systematics. Within Tetraclitidae, the diametric and monometric growth patterns and number of rows of parietal tubes in the shells are key characteristics used to infer evolutionary trends. We used molecular analysis based on seven genes (mitochondrial COI, 16S and 12S rRNA, and nuclear EF1, RPII, H3, and 18S rRNA) to test two traditional phylogenetic hypothesis: (1) Tetraclitid barnacles are divided into two major lineages, which are distinguished according to monometric and diametric shell growth patterns, and (2) the evolutionary trend in shell parietal development began with a solid shell, which developed into a single tubiferous shell, which then developed into multitubiferous shells. The results indicated that Tetraclitinae and Newmanellinae are not monophyletic, but that Austrobalaninae and Tetraclitellinae are. The phylogram based on the genetic data suggested that Bathylasmatidae is nested within the Tetraclitidae, forming a sister relationship with the Austrobalaninae and Tetraclitinae/Newmanellinae clade. Within the Tetraclitinae/Newmanellinae clade, the genera Tetraclita (multitubiferous shell), Tesseropora (single tubiferous shell), and Yamaguchiella (multitubiferous shell) are polyphyletic. The results suggested that shell morphology and growth patterns do not reflect the evolutionary history of Tetraclitidae, whereas the arthropodal characteristics are informative.

Complete mitochondrial genome of the acorn barnacle Striatobalanus amaryllis (Crustacea: Maxillopoda): the first representative from Archaeobalanidae.

The mitochondrial genome of the barnacle Striatobalanus amaryllis (Sessilia: family Archaeobalanidae) is 15,063 bp in length. All the 13 protein-coding genes (PCGs) initiate with ATD codon (ATG, ATA or ATT). Four PCGs (COX3, ND3, ND4 and ND4L) end with incomplete stop codon (T- -). Four PCGs (ND1, ND4, ND4L and ND5) are encoded on the light strand (underlined below). Refer to the pancrustacean ground pattern, there are not less than seven tRNAs rearranged in the S. amaryllis mitochondrial genome, including tRNA(Ala), tRNA(Glu)/tRNA(Ser)((AGY)), tRNA(Pro)/tRNA(Thr), tRNA(Pro)/tRNA(Thr), tRNA(Tyr), tRNA(Lys), tRNA(Gln) and tRNA(Cys). Three tRNAs (tRNA(Lys), tRNA(Gln) and tRNA(Cys)) are rearranged between S. amaryllis and Tetraclita japonica (Sessilia: Tetraclitidae), meanwhile one tRNA (tRNA(Cys)) inverted from one strand to another. Compared with Megabalanus volcano (Sessilia: Balanidae), an inversion of one large gene block is identified (including three PCGs and three tRNAs) in S. amaryllis mitochondrial genome: tRNA(Phe)-ND5-tRNA(His)-ND4-ND4L-tRNA(Pro).

The complete mitochondrial genome of common fouling barnacle Amphibalanus amphitrite (Darwin, 1854) (Sessilia: Balanidae) reveals gene rearrangements compared to pancrustacean ground pattern.

Here we present the complete mitochondrial genome of the common fouling barnacle, Amphibalanus amphitrite (Sessilia: Balanidae). Refer to pancrustacean mitochondrial ground pattern, seven conserved genes blocks are found in A. amphitrite mitochondrial genome. On the other hand, translocations of at least six tRNAs (trnA, trnE/trnS2, trnP/trnT, trnK, trnQ and trnC) are identified and translocation and inversion occurred simultaneously in one tRNAs (trnY). Comparison among the acorn barnacle mitogenomes reveals inversion of a six-gene block (trnP-nd4L-nd4-trnH-nd5-trnF) between A. amphitrite and Megabalanus. Volcano (Balanidae), suggesting non-conserved gene order even at intrafamilial level. The three species share three conserved genes blocks, of which the two are derived from the pancrustacean ground pattern and represent synapomorphies of acorn barnacles. In sum, large-scale gene rearrangements are observed in A. amphitrite mitochondrial genome as compared to the pancrustacean ground pattern and other barnacle species.

Morphological and host specificity evolution in coral symbiont barnacles (Balanomorpha: Pyrgomatidae) inferred from a multi-locus phylogeny.

Coral-inhabiting barnacles (Thoracica: Pyrgomatidae) are obligatory symbionts of scleractinian and fire corals. We attempted to reconstruct the phylogeny of coral-inhabiting barnacles using a multi-locus approach (mitochondrial 12S and 16S rRNA, and nuclear EF1, H3 and RP gene sequences, total 3532bp), which recovered a paraphyletic pattern. The fire-coral inhabiting barnacle Wanella milleporae occupied a basal position with respect to the other coral inhabiting barnacles. Pyrgomatids along with the coral-inhabiting archaeobalanid Armatobalanus nested within the same clade and this clade was subdivided into two major lineages: Armatobalanus+Cantellius with species proposed to be the ancestral stock of extant coral barnacles, and the other comprising the remaining genera studied. Ancestral state reconstruction (ASR) suggested multiple independent fusions and separations of shell plates and opercular valves in coral barnacle evolution, which counters the traditional hypothesis founded on a scheme of morphological similarities. Most of the coral barnacles are restricted to one or two coral host families only, suggesting a trend toward narrow host range and more specific adaptation. Furthermore, there is a close linkage between coral host usage and phylogenetic relationships with sister taxa usually being found on the same coral host family. This suggests that symbiotic relationships in coral-inhabiting barnacles are phylogenetically conserved and that host associated specialization plays an important role in their diversification.

Zoogeography of intertidal communities in the West Indian Ocean as determined by ocean circulation systems: patterns from the Tetraclita barnacles.

The Indian Ocean is the least known ocean in the world with the biogeography of marine species in the West Indian Ocean (WIO) understudied. The hydrography of WIO is characterized by four distinct oceanographic systems and there were few glacial refugia formations in the WIO during the Pleistocene. We used the widely distributed intertidal barnacle Tetraclita to test the hypothesis that the distribution and connectivity of intertidal animals in the WIO are determined by the major oceanographic regime but less influenced by historical events such as Pleistocene glaciations. Tetraclita were studied from 32 locations in the WIO. The diversity and distribution of Tetraclita species in the Indian Ocean were examined based on morphological examination and sequence divergence of two mitochondrial genes (12S rDNA and COI) and one nuclear gene (histone 3, H3). Divergence in DNA sequences revealed the presence of seven evolutionarily significant units (ESUs) of Tetraclita in WIO, with most of them recognized as valid species. The distribution of these ESUs is closely tied to the major oceanographic circulation systems. T. rufotincta is distributed in the Monsoonal Gyre. T. ehsani is present in the Gulf of Oman and NW India. Tetraclita sp. nov. is associated with the Hydrochemical Front at 10°S latitude. T. reni is confined to southern Madagascan and Mauritian waters, influenced by the West Wind Drift. The endemic T. achituvi is restricted to the Red Sea. Tetraclita serrata consists of two ESUs (based on mtDNA analysis) along the east to west coast of South Africa. The two ESUs could not be distinguished from morphological analysis and nuclear H3 sequences. Our results support that intertidal species in the West Indian Ocean are associated with each of the major oceanographic circulation systems which determine gene flow. Geographical distribution is, however, less influenced by the geological history of the region.

Host-associated speciation in the coral barnacle Wanella milleporae (Cirripedia: Pyrgomatidae) inhabiting the Millepora coral.

Speciation by host shift is a common phenomenon observed in many symbiotic animals. The symbiont-host interaction is highly dynamic, but it is poorly documented in the marine realm. In the present study, we examined the genetic and morphological differentiation of the coral barnacle Wanella milleporae (obligate to fire corals) collected from four different Millepora host species in Taiwan to investigate the host specificity of this barnacle. Phylogenetic analysis of mitochondrial COI gene for 241 individuals of Wanella revealed five distinct clades, whose sequence divergences are comparable to values between other cogeneric barnacle species. The five clades also differ in shell and opercular plate morphology and colour. Genetic and morphological differentiations together strongly suggest the presence of cryptic species. Although the five clades do not display species-level host specificity, they showed a significant difference in preference on host growth form. Clades 1 and 2 were predominantly found on encrusting Millepora exaesa and Millepora platyphylla, while clades 3, 4 and 5 live exclusively on branching-form fire corals Millepora dichotoma and Millepora tenella. Phylogeny inferred from the combined mitochondrial COI, 16S and 12S (2182 bp) analysis suggests the division of the five clades into two major lineages congruent with the morphology of the host coral. Multiple independent invasions to the same form of host and subsequent speciation are evident in the Red Sea and Taiwan. Our results indicate that ecological/sympatric speciation could occur in marine symbiotic invertebrates through host shift and specialization. It appears that, as in their terrestrial counterparts, host-symbiont radiations in the marine realm are more prevalent than we expected and thus warrant further investigation.