Subclass Octocorallia Research Articles

Early development and coloniality in Oligophylloides from the Devonian of Morocco-Are Heterocorallia Palaeozoic octocorals?

Heterocorals represent an enigmatic group of Palaeozoic corals, known from relatively short time intervals in the Devonian and Carboniferous periods. The major differences between Heterocorallia and other Palaeozoic corals are the lack of an external theca (epitheca), lack of calices and the presence of dichotomously dividing septa-like structures. Heterocoral skeleton was presumably externally covered by the soft tissue and each branch of their skeleton has, until now, been regarded as a corallite–a skeleton of a single polyp. We investigated upper Famennian Oligophylloides from Morocco, focussing on branching processes, wall structure, previously poorly known initial growth stages and the growing tip, described here for the first time. We demonstrate that Oligophylloides shows a unique colony development not known in any group of anthozoans possessing a septate-like architecture and suggest that the previously postulated homology between true septa in hexa- and rugose corals on one hand, and Oligophylloides on the other, must be rejected. Based on the skeleton structure and branching patterns, we postulate, contrary to former ideas, that the stem and branches of heterocorals represent the skeleton of a multi-polyp colonial coral, similar to many extant octocorals. We found numerous potential homologies with octocoral skeletons (notably the Keratoisidinae within the Isididae) and, as a result, we propose the inclusion of the order Heterocorallia within the subclass Octocorallia. This suggestion requires, however, further research on the other taxa of heterocorals. We also propose some changes to the morphological terminology for the Heterocorallia.

Temporal Variation in the Microbiome of Tropical and Temperate Octocorals.

Bacterial members of the coral holobiont play an important role in determining coral fitness. However, most knowledge of the coral microbiome has come from reef-building scleractinian corals, with far less known about the nature and importance of the microbiome of octocorals (subclass Octocorallia), which contribute significantly to reef biodiversity and functional complexity. We examined the diversity and structure of the bacterial component of octocoral microbiomes over summer and winter, with a focus on two temperate (Erythropodium hicksoni, Capnella gaboensis; Sydney Harbour) and two tropical (Sinularia sp., Sarcophyton sp.; Heron Island) species common to reefs in eastern Australia. Bacterial communities associated with these octocorals were also compared to common temperate (Plesiastrea versipora) and tropical (Acropora aspera) hard corals from the same reefs. Using 16S rRNA amplicon sequencing, bacterial diversity was found to be heterogeneous among octocorals, but we observed changes in composition between summer and winter for some species (C. gaboensis and Sinularia sp.), but not for others (E. hicksoni and Sarcophyton sp.). Bacterial community structure differed significantly between all octocoral species within both the temperate and tropical environments. However, on a seasonal basis, those differences were less pronounced. The microbiomes of C. gaboensis and Sinularia sp. were dominated by bacteria belonging to the genus Endozoicomonas, which were a key conserved feature of their core microbiomes. In contrast to previous studies, our analysis revealed that Endozoicomonas phylotypes are shared across different octocoral species, inhabiting different environments. Together, our data demonstrates that octocorals harbour a broad diversity of bacterial partners, some of which comprise 'core microbiomes' that potentially impart important functional roles to their hosts.

The skeletome of the red coral Corallium rubrum indicates an independent evolution of biomineralization process in octocorals

BackgroundThe process of calcium carbonate biomineralization has arisen multiple times during metazoan evolution. In the phylum Cnidaria, biomineralization has mostly been studied in the subclass Hexacorallia (i.e. stony corals) in comparison to the subclass Octocorallia (i.e. red corals); the two diverged approximately 600 million years ago. The precious Mediterranean red coral, Corallium rubrum, is an octocorallian species, which produces two distinct high-magnesium calcite biominerals, the axial skeleton and the sclerites. In order to gain insight into the red coral biomineralization process and cnidarian biomineralization evolution, we studied the protein repertoire forming the organic matrix (OM) of its two biominerals.ResultsWe combined High-Resolution Mass Spectrometry and transcriptome analysis to study the OM composition of the axial skeleton and the sclerites. We identified a total of 102 OM proteins, 52 are found in the two red coral biominerals with scleritin being the most abundant protein in each fraction. Contrary to reef building corals, the red coral organic matrix possesses a large number of collagen-like proteins. Agrin-like glycoproteins and proteins with sugar-binding domains are also predominant. Twenty-seven and 23 proteins were uniquely assigned to the axial skeleton and the sclerites, respectively. The inferred regulatory function of these OM proteins suggests that the difference between the two biominerals is due to the modeling of the matrix network, rather than the presence of specific structural components. At least one OM component could have been horizontally transferred from prokaryotes early during Octocorallia evolution.ConclusionOur results suggest that calcification of the red coral axial skeleton likely represents a secondary calcification of an ancestral gorgonian horny axis. In addition, the comparison with stony coral skeletomes highlighted the low proportion of similar proteins between the biomineral OMs of hexacorallian and octocorallian corals, suggesting an independent acquisition of calcification in anthozoans.

Global Neuropeptide Annotations From the Genomes and Transcriptomes of Cubozoa, Scyphozoa, Staurozoa (Cnidaria: Medusozoa), and Octocorallia (Cnidaria: Anthozoa).

During animal evolution, ancestral Cnidaria and Bilateria diverged more than 600 million years ago. The nervous systems of extant cnidarians are strongly peptidergic. Neuropeptides have been isolated and sequenced from a few model cnidarians, but a global investigation of the presence of neuropeptides in all cnidarian classes has been lacking. Here, we have used a recently developed software program to annotate neuropeptides in the publicly available genomes and transcriptomes from members of the classes Cubozoa, Scyphozoa, and Staurozoa (which all belong to the subphylum Medusozoa) and contrasted these results with neuropeptides present in the subclass Octocorallia (belonging to the class Anthozoa). We found three to six neuropeptide preprohormone genes in members of the above-mentioned cnidarian classes or subclasses, each coding for several (up to thirty-two) similar or identical neuropeptide copies. Two of these neuropeptide preprohormone genes are present in all cnidarian classes/subclasses investigated, so they are good candidates for being among the first neuropeptide genes evolved in cnidarians. One of these primordial neuropeptide genes codes for neuropeptides having the C-terminal sequence GRFamide (pQGRFamide in Octocorallia; pQWLRGRFamide in Cubozoa and Scyphozoa; pQFLRGRFamide in Staurozoa). The other primordial neuropeptide gene codes for peptides having RPRSamide or closely resembling amino acid sequences. In addition to these two primordial neuropeptide sequences, cnidarians have their own class- or subclass-specific neuropeptides, which probably evolved to serve class/subclass-specific needs. When we carried out phylogenetic tree analyses of the GRFamide or RPRSamide preprohormones from cubozoans, scyphozoans, staurozoans, and octocorallia, we found that their phylogenetic relationships perfectly agreed with current models of the phylogeny of the studied cnidarian classes and subclasses. These results support the early origins of the GRFamide and RPRSamide preprohormone genes.

Molecular phylogeny and diversity of sea pens (Cnidaria: Octocorallia: Pennatulacea) with a focus on shallow water species of the northwestern Pacific Ocean

The order Pennatulacea, commonly known as sea pens, are colony-forming benthos belonging within subclass Octocorallia (Anthozoa, Cnidaria). Sea pens are found worldwide from shallow to deep waters, and they are important components in sandy and muddy environments. Thus far, there has been only one molecular study focusing on the phylogenetic relationships within the order Pennatulacea, which mainly treated deep-sea species, and thus information on shallow water species is still lacking. On a regional scale, the diversity of sea pens in the northwestern Pacific, including Japan and Palau, has not been well investigated. In this research, we aimed to: (1) more accurately resolve the phylogenetic relationships of sea pens with the inclusion of shallow water species, and (2) obtain a better understanding of the diversity of sea pens in Japan and Palau. Specimens were collected by SCUBA and dredging from the Ryukyu Islands in southern Japan, and from mainland Japan and Palau, and identified to at least the genus level by their morphological traits. Construction of phylogenetic trees with concatenated sequences including the mitochondrial mutS-like protein DNA mismatch repair gene mtMutS and the NADH dehydrogenase subunit 2 ND2 region were performed. The p-distances of mtMutS were calculated for estimation of species number following McFadden et al. (2011). Molecular data for 12 families and 20 genera of sea pens were used in this study. This most comprehensive study including shallow water taxa provided us with more knowledge of phylogenetic relationships. The resulting phylogenetic trees showed a topology distinguished by four large clades (clades 1–4). Families Veretillidae and Echinoptilidae are shown as not the earliest-diverging taxa. Virgulariidae and Scleroptilidae are shown as polyphyletic groups, and our results reconfirm that families Pennatulidae, Kophobelemnidae and Umbellulidae are not monophyletic groups. Overall, we collected and examined an estimated 18 species from the Ryukyu Islands, 16 species from mainland Japan, and five species from Palau. Some of these specimens represented new records from Ryukyu Islands and Palau. Previous records of these sea pens did not exist likely due to a lack of diversity research in sandy and muddy areas. These results demonstrate that many sea pens discoveries likely remain in shallow waters of the Pacific.

Alcyonacea awakens: Palaeobiology and palaeoecology of Palaeozoic octocorals known from their sclerites

Most Alcyonacea (subclass Octocorallia) have skeletons made up of small calcareous pieces called sclerites that are difficult to both preserve and recognize, which explains the scarce and irregular fossil record of the group. In this work, we study 56 geological samples bearing Syringoalcyon, a genus constituted by Alcyonacea represented by sclerites encrusting the outer walls and stolons of a syringoporoid coral. These samples come from 18 Silurian to mostly Carboniferous localities in Canada, USA, Mexico, Morocco, Algeria, Spain, Iran, and China. A morphological and numerical study was carried out to determine the main morphological and palaeobiological features of the sclerites and the Alcyonacea itself and to establish a new genus for these sclerites. The study facilitated distinguishing four sclerite morphotypes (spindle, elongate spindle, club, and arrowhead). Live sclerites can be attached through biotic or abiotic linkages to biotic substrate patches by insertion or cementation. Spindle sclerites arranged in vertical fences are the most common model, but other arrangements such as stacking or short horizontal fences have been observed even in a single specimen. The morphotypes, dimensions of the sclerites, substrates, and types of arrangement observed are well known in Recent Alcyonacea. According to the arrangements of the sclerites, the alcyonacean morphology was different depending on the shape and dimensions of the substrate. This Syringoporidae–Alcyonacea association is a good example of ecological engineering, but several data suggest that the relationship between these two corals was closer than hard substrate colonization.

Identification of Genes for Synthesis of the Blue Pigment, Biliverdin IXα, in the Blue Coral Heliopora coerulea.

Heliopora coerulea is the only species in the subclass Octocorallia that has a crystalline aragonite skeleton. The skeleton has been reported to contain the blue pigment, biliverdin IXα, which is formed by heme oxygenase (HO) during heme decomposition. There is little information regarding gene expression in H. coerulea; therefore, the biosynthesis pathway for biliverdin IXα is poorly understood. To identify the genes related to heme synthesis and degradation, metatranscripts of H. coerulea and its symbiont Symbiodinium spp. were sequenced and separated from the host- and symbiont-derived sequences. From the metatranscriptome analyses, all genes for heme synthesis and three HOs were isolated from the host and symbiont. From our phylogenetic and amino acid analysis, we noted that one of the HO isoforms in the host coral was predicted to possess HO activity. However, biliverdin reductase, which reduces biliverdin to bilirubin, was not identified in the present study. Similarly, biliverdin reductase was not identified in the transcripts of the red coral Corallium rubrum, a species that also belongs to Octocorallia. However, genes related to heme synthesis and HO were found in C. rubrum. We speculate that Heliopora coerulea can produce biliverdin and accumulate it in the skeleton, while red corals and other Octocorallia species cannot. Further information from molecular studies of H. coerulea will provide insights into the synthesis of biliverdin IXα, the blue pigment in the hard crystalline aragonite skeleton, and will be fundamental to future ecological and physiological studies.

Nomenclatural note on the homonymy between the octocoral genus Dendrobrachia Brook 1889 and the entoproct phylum Dendrobrachia Xian-Guan, Bergström, Xio-Ya and Jie 2006.

Dendrobrachia was proposed by Xian-Guan et al. (2006) as the name of a new phylum of entoproct-like animals from the Lower Cambrian (Yunnan Province, China). This name was however preoccupied by the octocoral Dendrobrachia Brook 1889, which position within the subclass Octocorallia is currently uncertain (Opresko and Bayer 1991; Berntson et al. 1999, 2001). Based on the principles of homonymy and priority (Articles 52 and 23, respectively; ICZN 1999), a substitute name for the entoproct Dendrobrachia is necessary, and I propose Dendrobrachion (based on the Greek brachion, for arm).

Distribution of Very-Long-Chain Fatty Acids between Molecular Species of Different Phospholipid Classes of Two Soft Corals

Fatty acids (FAs) of soft corals contain two very-long-chain tetracosapolyenoic acids (TPA, 24:5n-6 and 24:6n-3), which are chemotaxonomic markers of all species of the subclass Octocorallia. The distribution of TPA in molecular species of different phospholipid (PL) classes was investigated for the first time in the soft corals Sinularia macropodia and Capnella sp. From shallow waters of Vietnam. Phosphatidylethanolamine (PE), phosphatidylcholine (PC), phosphatidylserine (PS), and phosphatidylinositol (PI) were the major PL classes of S. macropodia and Capnella sp. More than thirty two molecular species of these four PL classes were determined by high resolution tandem mass spectrometry. 18:1e/20:4 PE, 18:0e/20:4 PC, 18:0e/24:5 PS, and 18:0/24:5 PI were the major molecular species of PL in both coral species. PE, PC, and PS mainly consisted of alkyl acyl and alkenyl acyl forms, but diacyl forms predominated in PI. TPA were the principal FAs in PS and PI, whereas 20:4n-6 was more abundant in PE and PC. Selective incorporation of TPA in the molecules of PS and PI are supposed to be a specific feature of the biosynthesis of PL in alcyonarians. To study the trophic and symbiotic relationships of soft corals, some molecular species of PS and PI with TPA may be applied as lipid molecular markers of coral polyps.

Gorgonia mariae and Antillogorgia bipinnata populations inferred from compensatory base change analysis of the internal transcribed spacer 2

The systematics within some families of octocorals (Class Anthozoa: Sub-class Octocorallia) remains uncertain in terms of morphological variability and unresolved molecular phylogenies. Elucidating the phylogenetic relationships among octocorals can help for understanding the origin of its huge biodiversity and optimizing conservation plans. The phylogenetic relationships within Gorgoniidae family remain highly polyphyletic. This research explores Gorgonia mariae and Antillogorgia bipinnata populations from several study sites in the Caribbean sea using for the first time the compensatory base changes (CBCs) analysis of the internal transcribed spacer 2 (ITS2) as a molecular tool to elucidate the phylogenetic relationships within the gorgonians. In addition, the mitochondrial gene mtMutS was sequenced in order to complement the nuclear information. This research shows that the presence of CBCs and hemi-CBCs is useful as a complementary tool for providing insights between octocoral species and populations, as well as an approach to figure out the origin of the octocorals biodiversity.

Reproductive biology of the deep-water coral Acanella arbuscula (Phylum Cnidaria: Class Anthozoa: Order Alcyonacea), northwest Atlantic

Knowledge of the reproductive life-history of deep-water corals is important for assessing their vulnerability to anthropogenic impacts. Yet, the reproductive biology of many deep-water corals, especially members of the subclass Octocorallia, has not been examined. We used histological techniques to describe the reproductive biology of the deep-water gorgonian coral Acanella arbuscula from the northwest Atlantic. All colonies examined were gonochoric, and no embryos or planula larvae were observed in the polyps. Mean polyp-level fecundity (females: 21.0±17.5 oocytes polyp−1, and males: 13.9±13.5 sperm sacs polyp−1) is high compared to other deep-water gorgonians, and polyps closer to the branch tips had the highest fecundities in both females and males. The presence of large oocytes (maximum diameter 717.8μm) suggests that A. arbuscula produces lecithotrophic larvae. Despite the potentially high fecundity and small size at first reproduction, the paucity of information on dispersal and recruitment, combined with its longevity, vulnerability to bottom fishing gear, and ecological role as a structure-forming species, still warrants the classification of A. arbuscula as a vulnerable marine ecosystem indicator.

The Mitochondrial Genome of Paraminabea aldersladei (Cnidaria: Anthozoa: Octocorallia) Supports Intramolecular Recombination as the Primary Mechanism of Gene Rearrangement in Octocoral Mitochondrial Genomes

Sequencing of the complete mitochondrial genome of the soft coral Paraminabea aldersladei (Alcyoniidae) revealed a unique gene order, the fifth mt gene arrangement now known within the cnidarian subclass Octocorallia. At 19,886 bp, the mt genome of P. aldersladei is the second largest known for octocorals; its gene content and nucleotide composition are, however, identical to most other octocorals, and the additional length is due to the presence of two large, noncoding intergenic regions. Relative to the presumed ancestral octocoral gene order, in P. aldersladei a block of three protein-coding genes (nad6–nad3–nad4l) has been translocated and inverted. Mapping the distribution of mt gene arrangements onto a taxonomically comprehensive phylogeny of Octocorallia suggests that all of the known octocoral gene orders have evolved by successive inversions of one or more evolutionarily conserved blocks of protein-coding genes. This mode of genome evolution is unique among Metazoa, and contrasts strongly with that observed in Hexacorallia, in which extreme gene shuffling has occurred among taxonomic orders. Two of the four conserved gene blocks found in Octocorallia are, however, also conserved in the linear mt genomes of Medusozoa and in one group of Demospongiae. We speculate that the rate and mechanism of gene rearrangement in octocorals may be influenced by the presence in their mt genomes of mtMutS, a putatively active DNA mismatch repair protein that may also play a role in mediating intramolecular recombination.

Complete mitochondrial genomes of two Japanese precious corals, Paracorallium japonicum and Corallium konojoi (Cnidaria, Octocorallia, Coralliidae): Notable differences in gene arrangement

Precious coral are taxonomically a group of corals that belong to the family Coralliidae within the order Alcyonacea, subclass Octocorallia, and class Anthozoa, whose skeletal axes are used for jewelry. They are distributed in the Mediterranean Sea and in waters adjacent to Japan, Taiwan, Midway Island and the Hawaiian Islands. The genus Corallium of the family Coralliidae was recently divided into two genera, Corallium and Paracorallium, based on morphological observations, but insufficient molecular evidence to support this classification has been presented to date. We determined for the first time the complete mitochondrial genome sequence of two precious corals P. japonicum and C. konojoi, in order to clarify their systematic positions. The circular mitochondrial genomes of P. japonicum and C. konojoi are 18,913 bp and 18,969 bp in length, respectively, and encode 13 typical energy pathway protein coding genes ( nad1– 6, nad4L, cox1– 3, cob, atp6 and atp8), two ribosomal RNA genes ( rns and rnl), a transfer RNA ( trnM) and a mismatch repair gene homologue msh1. The two genomes have an overall nucleotide sequence identity of 97.5%, which is comparable to that between Acanella eburnea and Keratoisidinae sp. belonging to Octocorallia. Surprisingly, however, their gene arrangements were not identical. Phylogenetic analyses using seven complete mitochondrial genome sequences belonging to species in the subclass Octocorallia indicated that within the subclass, at least three gene order rearrangement events occurred during evolution. Our results support the validity of the morphological classification that separated the family Coralliidae into two genera, Corallium and Paracorallium.

Limitations of mitochondrial gene barcoding in Octocorallia

The widespread assumption that COI and other mitochondrial genes will be ineffective DNA barcodes for anthozoan cnidarians has not been well tested for most anthozoans other than scleractinian corals. Here we examine the limitations of mitochondrial gene barcoding in the sub-class Octocorallia, a large, diverse, and ecologically important group of anthozoans. Pairwise genetic distance values (uncorrected p) were compared for three candidate barcoding regions: the Folmer region of COI; a fragment of the octocoral-specific mitochondrial protein-coding gene, msh1; and an extended barcode of msh1 plus COI with a short, adjacent intergenic region (igr1). Intraspecific variation was <0.5%, with most species exhibiting no variation in any of the three gene regions. Interspecific divergence was also low: 18.5% of congeneric morphospecies shared identical COI barcodes, and there was no discernible barcoding gap between intra- and interspecific p values. In a case study to assess regional octocoral biodiversity, COI and msh1 barcodes each identified 70% of morphospecies. In a second case study, a nucleotide character-based analysis correctly identified 70% of species in the temperate genus Alcyonium. Although interspecific genetic distances were 2× greater for msh1 than COI, each marker identified similar numbers of species in the two case studies, and the extended COI + igr1 + msh1 barcode more effectively discriminated sister taxa in Alcyonium. Although far from perfect for species identification, a COI + igr1 + msh1 barcode nonetheless represents a valuable addition to the depauperate set of characters available for octocoral taxonomy.

Recent harvest records of commercially valuable precious corals in the Ryukyu Archipelago

Data, including depth, temperature and substrate, are reported for 143 colonies of 3 spe- cies of precious corals (Subclass Octocorallia; Family Coralliidae) collected in the Ryukyu Archipel- ago from June 2005 to May 2008. Colonies were collected by a commercial harvesting company using a remotely-operated vehicle (ROV) and a manned submersible, and identified tentatively as Para- corallium japonicum, Corallium elatius and Corallium konojoi. The data suggest that these species live deeper in lower latitudes (Amami, Okinawa and Ishigaki regions) than in higher latitudes (south- ern Kagoshima). Colonies of C. elatius may be larger at lower latitudes than at higher latitudes, but with the data available so far this cannot be definitely determined. Size differences may reflect har- vest history, not physical or biological factors. (The more southern regions have been exploited more recently than the northern region.) There has not yet been enough data made available to estimate the resource of precious corals remaining in the Ryukyu Archipelago. More studies of their taxonomy and biology, especially growth rates, age and size at fertility and timing of reproduction, and data on biomass are necessary in order to make meaningful estimates.

Exploring the utility of an indel-rich, mitochondrial intergenic region as a molecular barcode for bamboo corals (Octocorallia: Isididae)

The DNA barcoding initiative has advocated the use of the 5′-end (∼ 658 bp) of mitochondrial (mt) cytochrome c oxidase subunit 1 ( cox1) to genetically distinguish species. However, this has proven difficult within the subclass Octocorallia due to extraordinarily low substitution rates within mt protein-coding genes. Intergenic regions (IGRs), which have been little examined among octocorals, may be subject to high mutation rates and have proven useful target regions at both the interspecific and population levels of metazoans. Herein we examine a mt IGR ( igr4) between the cytochrome b ( cob) and NADH dehydrogenase subunit 6 ( nad6) genes among species of the bamboo coral subfamily Keratoisidinae to evaluate its utility for barcoding and phylogenetic studies. Among 77 keratoisidin specimens, we found igr4 to vary in length between either 42 bp ( Acanella Gray, 1870 and Orstomisis Bayer, 1990) or 302–605 bp ( Isidella Gray, 1857 , Lepidisis Verrill, 1883, Keratoisis Wright, 1869 , and two undescribed genera). We interpreted the short igr4 sequence of Acanella eburnea (Pourtalès, 1868) as potentially indicative of additional mt genome-related novelties and thus sequenced its entire mt genome; gene content and gene order were the same as in a previously-sequenced bamboo coral mt genome. Alignment of the longer igr4 sequences included 108 parsimony-informative characters, as well as numerous indels ranging from 2–262 bp in length. Uncorrected pairwise ‘ p’ distances indicated sequence variation of 0–27.2%, as compared to 0–4.8% among the same specimens for the MutS homolog ( msh1), currently the most widely sequenced octocorallian mt gene, and <0.4% for cox1 for a subset of the taxa. Despite the greater levels of variation, fewer unique haplotypes were observed at igr4 compared to msh1; however, in combination, the two gene regions revealed increased mt haplotype diversity relative to either gene region on their own.

Molecular Phylogeny and Divergence Time Estimation of the Soft Coral Dendronephthya gigantea (Alcyonacea: Nephtheidae)

Soft coral Dendronephthya gigantea (Verrill, 1864) is a conspicuous species dominating shallow sea waters of Jejudo Island, Korea. Recently its whole mitochondrial genome sequencing was completed by us and the sequence information provided an opportunity to test the age of Octocorallia and time of evolutionary separation between some representative orders of the subclass Octocorallia. Molecular phylogenetic analyses based on 13 mitochondrial protein encoding genes revealed a polyphyletic relationship among octocorallians representing two orders (Alcyonacea and Gorgonacea) and four families (Alcyoniidae, Nephtheidae, Briareidae, and Gorgoniidae). Estimates of divergence times among octocorallians indicate that the first splitting might occur around end of or after Cretaceous period (50-79 million years ago (Ma)). The age is relatively young compared to the long history of stony sea corals (>240 Ma). Taken together our result suggests a possible relatively recent radiating evolution at least in the order Alcyonacea and Gorgonacea. Molecular dating and phylogenetic analysis based on much broader taxon sampling and many genes might give an insight into this interesting hypothesis.

Octocorals (Coelenterata: Anthozoa: Octocorallia) of Isla del Coco, Costa Rica

The published literature on Isla del Coco (Cocos Island), Costa Rica reveals that until recent years the octocorals were among the least known marine invertebrates. Two of the three orders within the subclass Octocorallia, the Pennatulacea (sea pens) and Alcyonacea (soft corals, gorgonians and telestids) occur in Isla del Coco. From recent collections and research, the total octocorallian fauna presently accounts to three pennatulaceans, seven gorgonians, a soft coral, and one telestid. A sea pen, a telestid, and three of the gorgonians have been collected recently, and two of them are probably new species. The genus Pacifigorgia includes one species: P. curta, presently considered as endemic. There are two species of the genus Leptogorgia, one which presents a large distributional range along the Pacific coast of Costa Rica, L. alba, and another which is a new species only found in Isla del Coco and is yet to be described. Finally, an undescribed species related to the genus Rhodelinda was found attached to rodoliths. The other species cited in the literature, the gorgonian, Psammogorgia variabilis, and the pennatulacean, Ptilosarcus undulatus, need to be corroborated since we have not found them yet. Other species, including alcyoniians (soft corals), have been observed by submarine submersibles from 50 m down to 450 m. Some deep water species were collected during a Harbor Branch Oceanographic Institution expedition in 1986 with their research submersible the Johnson Sea Link, and four of them have been identified to genera. Several are expected to represent species new to science. Twelve species of octocorals are recorded here. Rev. Biol. Trop. 56 (Suppl. 2): 71-77. Epub 2008 August 29.

DNA sequences of the mitochondrial COI gene have low levels of divergence among deep-sea octocorals (Cnidaria: Anthozoa)

We are analyzing genetic diversity in deep-seamount octocorals with the ultimate goal of studying the effect of retention and dispersal of larvae on genetic population structure. Here we report on the sequence diversity of the mitochondrial cytochrome oxidase I (COI) gene among 11 species. Uncorrected pairwise sequence divergences ranged from 0.4–10.3% for comparisons among species spanning the intrageneric to interordinal levels. Relative to other invertebrates, these divergences are very low, suggesting that COI may not be useful as a genetic marker for studying dispersal among deep-sea octocoral populations. Possible explanations for the reduced rates of divergence observed include a lower rate of evolution for octocoral mitochondrial genomes and the presence of a gene, mtMSH, which may code for a mitochondrial DNA mismatch-repair system. We report the finding of mtMSH in three deep-sea octocorals (Acanthogorgia sp., Corallium ducale, and Paramuricea sp.), which brings the total published observations of this gene to six species, all in the subclass Octocorallia.

Phylogenetic relationships within the Octocorallia (Cnidaria: Anthozoa) based on nuclear 18S rRNA sequences

We determined the nuclear 18S rRNA sequences for 41 species of octocorals and used these to address the validity of the historical ordinal divisions and the current subordinal divisions within the subclass Octocorallia. We also explored the phylogenetic affinities of the species Dendrobrachia paucispina, which was originally classified in the order Antipatharia (subclass Ceriantipatharia) although polyp structure indicates it belongs in the subclass Octocorallia. Trees constructed using maximum likelihood techniques are incongruent with the current and historical taxonomy of the Octocorallia. There appeared to be three major clades of octocorals. The first clade included most, but not all, pennatulaceans as a monophyletic group. The second clade contained 21 species, representing all major octocoral groups other than pennatulaceans. The third clade contained members from three suborders of the Alcyonacea and one member of the Pennatulacea. These data could not be used to distinguish the branching order of the three major clades. The species D. paucispina had a close affinity with the genera Corallium and Paragorgia (Alcyonacea: Scleraxonia), although its morphology suggests it is more similar to the genus Chrysogorgia (Alcyonacea: Calcaxonia). The morphological character of dimorphism (the presence of both autozooids and siphonozooids within a single colony) corresponded loosely with the topology of the most likely trees, and a single origin of dimorphism could not be rejected. Despite sampling from the majority of families within the Octocorallia, many of the relationships within this group remain ambiguous.