Opercular Plates Research Articles

Barnacle-rich facies as a tool for palaeoenvironmental reconstructions

Palaeoenvironmental data are fundamental in determining the manifold impacts of climate change. This paper argues that sessile barnacles are an excellent palaeoenvironmental proxy: they are present in nearly all nearshore environments, and their shell consists of diagenetically stable low-magnesium calcite and grows fast enough to record short-term variations. To demonstrate their utility, specimens from several Western Mediterranean Pliocene and Pleistocene barnacle-rich deposits are analysed herein, using for the first time a combination of sedimentology, taphonomy, stable isotope geochemistry and detailed comparisons with modern counterparts. Within shelf carbonate systems, barnacle diversity is highest in the shallow, nearshore waters and decreases moving offshore, thus providing a good proxy for the reconstruction of water depth and distance from the coastline. Barnacle taphonomy is also informative. Well-preserved complete specimens are characteristic of protected areas, whereas less well-preserved specimens occur in high-energy areas. The presence/absence of opercular plates is also particularly relevant for evaluating hydrodynamic conditions. As regards the C and O stable isotope ratios, due to the porous and coarse-grained nature of the deposits in which barnacle remains are usually found, the shells are often exposed to meteoric water percolation during diagenesis. Among the analysed specimens, only those collected from fine-grained deposits display no evidence of alteration and have isotopic ratios in line with those of their modern counterparts. These fossils display intra-shell variations that in modern barnacles have been related to short-term environmental changes (e.g., seasonal cycles). These results demonstrate that barnacles can always be useful for detailed palaeoenvironmental reconstructions based on skeletal assemblages. Furthermore, with further research aimed at gathering more data and assessing potentially interfering signals, they could become useful proxies for palaeoseasonality.

Lost and found: Totton’s Minyaspis faroni revived and molecular evidence of paraphyly of Oxynaspis and Minyaspis

ABSTRACT The stalked barnacles Minyaspis faroni associated with antipatharians known from the southern Red Sea have been recently recorded in the northern Red Sea. Two genera of oxynaspids, Oxyaspis and Minyaspis, differ morphologically in the coverage of the capitulum. In Oxyaspis, the capitulum is covered by calcified plates, whereas in Minyaspis, the plates are reduced, and there is an uncalcified area between plates. Molecular analyses revealed that species with reduced plates do not cluster in the same clade, whereas species with full coverage and uncalcified capitula are found in the same clade. Our analysis indicates that the reduction of opercular plates in the epibiotic barnacles has occurred more than once in the barnacle evolutionary pathway. The reduction in shell plates’ number, size, shape and thickness is an adaptive character of epibiotic symbiosis. This mode of life, common in thoracican barnacles, leads to adaptive morphological changes. Hence, the morphology of shell plates is not a homologous feature but reflects parallel evolution.

Redescription of Pomatostegus stellatus (Abildgaard, 1789) and P. kroyeri Mörch, 1863 (Polychaeta: Serpulidae) from the Tropical American coasts.

Pomatostegus Schmarda, 1861 is a serpulid genus with three recognized species, mostly from tropical waters. Pomatostegus stellatus (Abildgaard, 1789), was described from the Caribbean Sea, and has been widely recorded in the Pacific and Indian oceans; P. kroyeri Mörch, 1863 was described from Puntarenas, Costa Rica; however, most records from the Tropical Eastern Pacific were referred to P. stellatus. In this work, the two species are redescribed using morphological characters. The main differences are in the shape of the Spirobranchus-type collar chaetae, opercular plate shape and the number of "free" circlets of spines without accompanying of opercular plates. Comments about characters of P. actinoceras Mörch, 1863, described from Philippines, and an identification key for the three species, are included.

Morphological and molecular evidence support the intertidal barnacle Octomeris intermedia Nilsson-Cantell, 1921 (Thoracica, Chthamalidae) as a valid species in Indo-Pacific waters.

Octomeris is a chthamalid intertidal barnacle with eight shell plates. There are currently two species of such barnacles: O. brunnea Darwin, 1854 (type locality in the Philippines), common in the Indo-Pacific region, and O. angulosa Sowerby, 1825, only recorded in South Africa. Octomeris intermedia Nilsson-Cantell, 1921, identified from the Mergui Archipelago in Myanmar, was considered to be conspecific with O. brunnea by Hiro (1939) based on samples collected in Taiwan. The morphological differences in shell and opercular plates between O. brunnea and O. intermedia are believed to be intra-specific variations due to different degrees of shell erosion. In the present study, the genetic and morphological differentiations of Octomeris in the Indo-Pacific region were examined. This study found two molecular clades (with inter-specific differences) based on the divergence in the COI genes, and the species also have distinct geographical distributions. The Octomeris brunnea clade covers samples collected from the Philippines and Taiwan waters and the other clade, which we argue is O. intermedia, is distributed in Phuket and Krabi, Thailand and Langkawi, Malaysia. Phuket and Krabi are located approximately 300 km south of the Mergui Archipelago, the type locality of O. intermedia. The morphology of samples collected from Thailand fits the type description of O. intermedia in Nilsson-Cantell (1921). Our study concludes that O. intermedia is a valid species based on morphological and molecular evidence.

Deep-water cirripedes colonizing dead shells of the cephalopod Nautilus macromphalus from New Caledonian waters.

Fossil cephalopods are frequently encrusted by epibionts; however, determining whether encrustation occurred prior to or post‐mortem to the host, and whether the final environment of deposition corresponds to the habitat of encrustation is complex. The present paper describes cirripede epibionts, their calcareous bases and their attachment scars on 6 post‐mortem shells of Nautilus macromphalus, collected from deep water off New Caledonia. The cirripedes have left both cemented calcareous bases of Hexelasma and scars associated with bioerosion and discoloration produced by verrucomorph barnacles. Live cirripedes included a Metaverruca recta, with articulated opercular plates and organic tissue (on a shell that had been exposed on the sea floor for at least 150 years), and specimens of Hexelasma velutinum, one of which was partly attached to an internal surface of a shell. The disposition of verrucomorphs indicates that most Nautilus shells were colonized post‐mortem rather than during a floating stage. However, as cirripedes are known to have colonized living Nautilus, some Hexelasma, preserved only as calcareous eroded bases, may represent specimens that settled on a living Nautilus. The degree of bioerosion and discoloration induced by verrucomorph barnacles varies according to the surface preservation of Nautilus shells, with deeper and discolored traces preserved on old and degraded shells. Traces made by verrucomorphs described here are ellipsoidal and a new ichnotaxon, Anellusichnus ellipticus, is proposed to accommodate them. Importantly, verrucomorphs and other cirripede taxa with membranous bases that were attached to pristine shells may not leave any substantial scars, and, thus, will be difficult to detect in the fossil record.

Operculum shape variation in Theodoxus Montfort, 1810 (Gastropoda: Neritidae).

The operculum morphology of neritid snails of genus Theodoxus Montfort, 1810 yields important species-specific taxonomic characters. This study is the first attempt to describe morphological differences in snails based on operculum shapes using a geometric morphometric approach. We examined the variability of opercular shapes between sexes and among populations and species based on 91 opercula of adult specimens belonging to six populations of three species of Theodoxus from the central Balkan and the southern border of the Pannonian plain. There are no sex-related differences in operculum shape and size in the studied species. The presence of shape variations influenced by size (allometry) was confirmed for T. danubialis (C. Pfeiffer, 1828) indicating that allometry could be a component of the morphological variation of this species. At the intraspecific level, phenotypic plasticity of operculum shape was found in T. danubialis and T. fluviatilis (Linnaeus, 1758). Of particular interest is the lack of morphological variability in the rare and endangered T. transversalis (C. Pfeiffer, 1828). At the species level a clear morphological distinction of T. fluviatilis from T. danubialis and T. transversalis was detected, confirming that the operculum with a rib could be used as a species-specific morphological character. The main morphological differences between species are an outwardly-stretched opercular/apophysal rib and a shortened tip of the opercular plate in T. fluviatilis, compared to the same structures in T. danubialis and T. transversalis.

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. maculosus sp. 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.

The fossil record of drilling predation on barnacles

Abstract The fossil record of drilling predation has been studied in detail for a few major invertebrate groups (bivalves, gastropods, brachiopods, and echinoids), while other prey (e.g., scaphopods, serpulids, decapods, and barnacles) have been largely neglected. Herein, we report on drilling predation using an extensive collection of Cretaceous–Quaternary barnacles (> 50,000 specimens). In total, 312 drill holes of predatory origin were found in Eocene–Holocene wall and opercular plates of balanomorph and scalpellomorph barnacles. The drilled specimens originated from localities in the USA, Jamaica, Panama, The Netherlands, Belgium, Antarctica, South Africa, Chile, and Venezuela, suggesting that drilling predation on barnacles was a worldwide phenomenon during the Cenozoic. Muricid gastropods are the inferred producers of the majority of the drill holes; two drill holes were likely caused by octopods. Drilling frequencies lack major temporal trends and appear low (

Novel mating modes on wave-swept shores: aerial copulation and sperm release in an intertidal stalked barnacle

Mating behavior of the intertidal stalked barnacle, Pollicipes polymerus, is unusual. Spermcast mating is unexpectedly common, but its prevalence and mechanisms of sperm release and capture are unknown. Moreover, copulation has never been observed in P. polymerus, despite possessing a well-developed penis and despite numerous attempts to observe it. This raises questions about whether spermcasting is a primary or secondary mode of mating in P. polymerus. Through field observations at sites in Barkley Sound, British Columbia (48°N, 125°W) in the northern hemisphere summers of 2012–2014, (a) the incidence of sperm leakage at low tide and (b) the type and prevalence of copulatory behaviors were quantified. Sperm leakage was an infrequent event: ~0.1 % of P. polymerus released a milky, viscous liquid between their opercular plates at low tide. Microscopic examination confirmed that this liquid contained abundant sperm, although sperm viability could not be verified. Some leaker individuals (31 % of 13 examined) contained newly released egg sacks, so sperm leakage in these may have been a post-mating response. However, the remaining leakers contained either fully mature egg masses (egg lamellae), or no eggs or sperm at all, suggesting that sperm leakage was an active process. Transects of P. polymerus beds revealed that sperm leakage at low tide was independent of most weather and tidal conditions. However, sperm leakage was more common lower in the intertidal at more wave-exposed sites. Rates of copulation in the field were about four times those of sperm leakage, suggesting that leakage may be a secondary mode of fertilization. Unique among barnacles, copulation occurred mostly when barnacles were partially emersed, shortly after contact with breaking waves on an incoming tide. Aerial copulation may allow P. polymerus to mate more reliably on shores with high wave exposure. Also unlike other barnacles, reciprocal copulation was occasionally observed in P. polymerus.

Biomineralisation during operculum regeneration in the polychaete Spirobranchus lamarcki

Formation of calcified biominerals is widespread in marine animals and is often associated with important elements of their biology, such as support and protection. Serpulid polychaetes are relatively understudied examples of biomineralisation despite their prominence in many marine ecosystems. An investigation of calcification in the regenerating opercular plate of the serpulid polychaete Spirobranchus (formerly Pomatoceros) lamarcki was performed using optical microscopy, calcein labelling and powder diffraction analysis. Worms were collected between January 2012 and June 2013 from East Sands beach, St Andrews, Scotland (56.33°N, 2.78°W). The earliest visible signs of calcification were birefringent grains. Later-stage regenerates displayed a complex mixture of calcified structures including grains, round, smooth tiles, and larger tiles with a rugged appearance. The plate matures by the growth and eventual merging of tiles into a contiguous crust. Calcein pulse-chase experiments showed the progression of calcification from the centre towards the edge of the plate, and powder diffraction analysis of three regenerative stages revealed a major shift in mineralogy from a predominantly calcitic to a predominantly aragonitic composition. The mechanisms underlying the shift are currently unknown. These are the first mineralogical data comparing different developmental stages in a serpulid operculum and contribute to the understanding of biomineralisation in this group.

Risks for larvae mediated by plasticity in hatching

AbstractRisks associated with benthic and planktonic development can be mediated by plasticity in hatching. The ability to delay hatching while awaiting favorable planktonic conditions, combined with the ability to accelerate hatching when encapsulated offspring are at risk, should be advantageous. We tested this predicted association of hatching plasticities with a barnacle. In the winter, broods of barnacles (Balanus glandula) reached hatching‐capable stages at widely varying times, but these broods hatched in the spring within about 2 weeks, consistent with a synchronizing environmental stimulus for hatching. In contrast, the same adults held subsequent broods (during later spring and summer) briefly. Either an environmental stimulus for hatching was not needed later in the season, or it was more frequently present. Dissections of brood lamellae that scattered smaller clumps of the encapsulated nauplii induced hatching. Crabs eating brooding adults had a similar effect: crabs broke the barnacles' tests, and many nauplii hatched. In contrast, when whelks ate barnacles, they left the barnacles' wall plates and opercula in place, and few nauplii were released. In some cases, numerous hatched nauplii were trapped within the test of the killed mother. At a field site with abundant whelks, many dead barnacles had opercular plates in place. Plasticity in hatching of broods adjusted risks for planktonic larvae against risks of death of the parent before release of embryos, but escape or death of brooded offspring depended on the kind of damage to the brooding mother and thus on the kind of predator. Although both predators killed brooding parents, subtle snails imposed a greater risk than crushing crabs.

The dynamics of alkaline phosphatase activity during operculum regeneration in the polychaete Pomatoceros lamarckii

Alkaline phosphatase enzymes are found throughout the living world and fulfil a variety of functions. They have been linked to regeneration, stem cells and biomineralisation in a range of animals. Here we describe the pattern of alkaline phosphatase activity in a spiralian appendage, the operculum of the serpulid polychaete Pomatoceros lamarckii. The P. lamarckii operculum is reinforced by a calcified opercular plate and is capable of rapid regeneration, making it an ideal model system to study these key processes in annelids. Alkaline phosphatase activity is present in mesodermal tissues of both intact and regenerating opercular filaments, in a strongly regionalised pattern correlated with major morphological features. Based on the lack of epidermal activity and the broad distribution of staining in mesodermal tissues, calcification- or stem cell-specific roles are unlikely. Transcriptomic data reveal that at least four distinct genes contribute to the detected activity. Opercular alkaline phosphatase activity is sensitive to levamisole. Phylogenetic analysis of metazoan alkaline phosphatases indicates homology of the P. lamarckii sequences to other annelid alkaline phosphatases, and shows that metazoan alkaline phosphatase evolution was characterised by extensive lineage-specific duplications.

Trichomycterus argos (Teleostei: Siluriformes: Trichomycteridae), a new species from the Doce River Basin, Eastern Brazil

Trichomycterus argos, new species, is described from the Rio Doce basin, situated in the Serra do Brigadeiro (part of theSerra da Mantiqueira) range, southeastern Brazil. The new species is diagnosed by the following characteristics: presenceof six branched rays in the pectoral fin; presence of pelvic fins; tip of nasal barbels extending to posterior border of oper-cular plate of odontodes; presence of a large foramen for ramus lateralis accessorius facialis, visible in dorsal view, in theparietosupraoccipital bone; transverse and straight border between the parietosupraoccipital and frontal bones; pectoral-fin ray prolonged as a filament; body covered with spots that seldom attain eye diameter; pelvic-fin origin placed one or two ocular diameters anterior to dorsal-fin origin; abscence of spots fused as elongated marks on dorsum or flank.

Microstructure and formation of the calcareous operculum in Pyrgopolon ctenactis and Spirobranchus giganteus (Annelida, Serpulidae)

The calcareous operculum of Pyrgopolonctenactis is composed of spherulitic prismatic structures. The opercular cup consists of regular spherulitic prismatic crystals; the talon has two layers, an inner with an irregular spherulitic prismatic structure (150 μm thick) and an outer with a regular spherulitic prismatic structure (110 μm thick). The outer regular structure has thick (1 μm) organic interprismatic sheets unique in biomineralization of this group, but similar to that of Bivalvia. We infer that control over biomineralization is stronger during the formation of the outer regular layer, with its thick organic interprismatic sheets, than during the formation of the inner irregular spherulitic prismatic structure, without such sheets. In Spirobranchus giganteus, opercular formation differs from that of P. ctenactis. S. giganteus has numerous pores in its opercular plate, and calcification starts with the formation of an outer irregularly oriented prismatic structure followed by an oriented prismatic structure without interprismatic sheets.

Economic Feasibility of Aquaculture of the Giant BarnacleAustromegabalanus psittacusin Southern Chile

The economic feasibility of culture of the giant barnacle Austromegabalanus psittacus (Molina, 1782) in southern Chile is analyzed. This species is traditionally exploited on a small scale by local fishermen, with average landings of 200 t/y. Cultures on a semi-industrial scale have been undertaken, from settlement of competent larvae present in the water column, through grow-out. Growth sustained by seston filtration produces specimens of a commercially viable size in a maximum of 24 mo. To determine the economic feasibility of cultures of these species, the investments required, production costs, yields, and the potential market prices of two products were evaluated: canned products and frozen meat, with the latter including opercular plates. To this effect, cultures were undertaken in suspended systems in Metri Bay (41°36′ S; 72°43′ W), and the following parameters were evaluated: average spat density in the artificial collector; mortality; gross annual production per longline; average gross weight per specimen, including shell; period from spat collection to harvest; operational costs; and labor requirements. Loss through processing and packaging, in addition to product yield and costs, were evaluated for both products in an industrial processing plant. To carry out market studies, a visit was undertaken to the Aomori Prefecture in Japan, where a similar species, Balanus rostratus or “mine fujit subo,” is commercialized. Prices of other species of crustaceans were also considered as a reference. Based on technical and economic findings, cash flows were budgeted and economic profitability indicators (net present value (NPV), internal rate of return (IRR), discounted payback period (DPBP), and economic profitability index (EPI)), were calculated. To incorporate risk and its effects on economic performance, a local sensitivity analysis was undertaken, considering a range of possible values for six critical variables and their influence on NPV and IRR. Elasticity measures, which express the percent change in NPV given a percent change in a variable, were estimated for each critical variable in both products. Furthermore, business viability limits were calculated, determining critical values for each variable separately, all others being held constant. Evidence and results indicate that culture of the giant barnacle is economically viable, with attractive economic indicators for both processed products (NPV above US$490,000, IRR above 36%, DPBP from 3–5 y, and EPI above 1.7 times). Projected income, profits, estimated cash flows, and economic indicators are higher in canned products, resulting from differences in product yields and market prices. For both products evaluated, the greatest capital investment corresponds to marine culture systems (longlines and spat collectors), and the most significant operational cost is labor used during the culture process. Sensitivity analysis indicates that, in general, this culture can withstand important changes in each critical variable, maintaining a positive NPV, especially in canned products. Comparing elasticity values among products, frozen meat presents a higher sensitivity level with greater elasticity for every critical variable. In both products, the variable with lowest incidence on NPV is processing and packing costs, and the most relevant variables are gross weight at harvest and sale price FOB. Results indicate that giant barnacle culture is technically and economically feasible. Thus, interesting possibilities emerge for the diversification of Chilean aquaculture as well as for other barnacle cultures, such as the “craca” of the Azores Islands, Portugal, and the “fujit subo” in Japan.

Description of a new species of sand-dwelling catfish of the genus Stenolicmus (Siluriformes; Trichomycteridae)

Stenolicmus ix, new species, is described from Igarapé Curuá, left tributary of the Rio Amazonas, Pará, Brazil. It can be distinguished from S. sarmientoi by the length of the nasal barbels that reach the base of the first opercular odontodes; length of the maxillary barbels that reach the posterior margin of the opercular odontode plate; seven well-developed opercular odontodes; seven well-developed interopercular odontodes; color pattern of the dorsal region of trunk composed of agglomerated chromatophores forming circular patches twice the diameter of the eye; proportionally large eyes, 11.8% HL; caudal peduncle tall, 11.6% SL, without dark bar at base of the caudal fin; length of the head proportionately larger, 17.9% SL; unbranched rays of caudal fin reaching distal margin of fin. Comparisons with other Sarcoglanidinae and Trichomycteridae are presented. Some comments on the systematics and phylogenetic relationships of the group are made.

A new species ofTemnosewellia(Platyhelminthes, Temnocephalida) ectosymbiont onVillopotamon thaii(Crustacea, Decapoda, Potamidae) from Vietnam

Damborenea C. & Brusa F. 2009. — A new species of Temnosewellia (Platyhelminthes, Temnocephalida) ectosymbiont on Villopotamon thaii (Crustacea, Decapoda, Potamidae) from Vietnam. Zoosystema 31 (2): 321-332.A new species of the genus Temnosewellia (Platyhelminthes, Temnocephalida, Temnocephalidae), Temnosewellia vietnamensis n. sp., is described from Quangnam Province, Vietnam, ectosymbiont on the external carapace of Villopotamon thaii Dang & Ho, 2003 (Crustacea, Decapoda, Potamidae). Records of temnocephalans from the region of Southeast Asia are superficial despite a great number of potential host species. Temnosewellia semperi (Weber, 1889), is the only known species and has been recorded from Aru, Java, Sumatra, Philippines, Malaysia, Thailand and China. In 2003, temnocephalans were reported for the first time from Vietnam which led to the current description of a new species based largely on characters from adults and eggs. The new species has five anterior tentacles; black pigment confined to the eyes; an ejaculatory sac; a cirrus straight that is not dilated and which has an obvious distal unspined region; anterior parenchyma with only two Haswell cells; yellow, slightly reniform eggs, that lack a peduncle and which are deposited on host carapace. The opercular plates of the eggs form a ring of seven almost rectangular shapes. The fracture plane of the operculum is parallel to the long axis of the egg. The great number of potential host species available in the Southeast Asia is taken as evidence that the region may harbour many other, yet undescribed, temnocephalan species.

Mortality of the Veined Rapa Whelk,Rapana venosa, in Relation to a Bloom ofAlexandrium monilatumin the York River, United States

Veined rapa whelks (Rapana venosa), carnivorous marine gastropods experienced significant mortality during an Alexandrium monilatum bloom in the lower York River, VA in September 2007. Rapa whelks stopped feeding as dissolved oxygen and chlorophyll concentrations increased with the development of the bloom. Whelk mortality was preceded by external signs of stress including reduced ventilation, inability to attach to hard substrates, periodic pumping of the opercular plate, and increased mucus production over a period of 24–48 h prior to death. High concentrations (2–7 µg g-1 tissue) of goniodimum A, a toxin produced by A. monilatum, were observed in bivalves attached to the shells of rapa whelks. Concentrations of goniodimum A in whelk foot tissue ranged from 0.02–8.39 µg g-1. Mortality of rapa whelks was 100%. Mortality of oysters (Crassostrea virginica) and northern quahogs (Mercenaria mercenaria) in the same flow through system was 0%. The symptoms displayed by the rapa whelks in the 24–48 h prior to death were indicative of paralysis and followed a similar time course documented for other molluscs exposed to toxic A. monilatum.

Host‐associated speciation in the coral barnacleWanella milleporae(Cirripedia: Pyrgomatidae) inhabiting theMilleporacoral

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.

A new species of Cantellius and a redescription of C. sextus (Hiro, 1938) (Cirripedia, Balanomorpha Pyrgomatidae) from the elephant skin coral, Pachyseris speciosa (Dana, 1846) (Scleractinia, Agariciidae) from Taiwan

Two species of Cantellius from Taiwan were identified from the elephant skin coral, Pachyseris speciosa Dana, 1846. Cantellius sextus was found on the underside of the coral plate and a new species, C. hoegi sp. nov., on the upper surface. The microdistribution indicates the different requirements of the two species. In the present study, both arthropodal and opercular plate characters of these two species were investigated using SEM techniques. Morphologically, C. hoegi is close to C. pallidus. However, the tergal scutal margins of C. pallidus are curved, whilst those of C. hoegi are straight, and its spur is narrower than that of C. pallidus. The apex of the scutum and tergum of C. hoegi forms a honeycomb-like surface, most probably the ‘imprint’ of the chitinous primordial valves. The separation of C. hoegi from C. pallidus is also supported by molecular analyses of three mitochondrial gene sequences (COI, 16S, and 12S rRNA). Cantellius hoegi differs from C. pallidus and C. sextus by >5% in all three mitochondrial genes (COI, 16S, and 12S rRNA) sequenced. The values of sequence divergence in 12S are comparable to the inter-specific divergence reported for other Cantellius and Savignium species. Interestingly, C. hoegi is not the sister group of C. pallidus, a morphologically similar species, in the present study. Further studies should focus on molecular phylogenetic analysis of Cantellius species.