Azooxanthellate Scleractinian Research Articles

Diversity patterns of the South African azooxanthellate scleractinians (Cnidaria: Anthozoa), with considerations of environmental correlates.

Azooxanthellate scleractinian corals, a group of species that lack a symbiotic relationship with dinoflagellates, are influenced by environmental variables at various scales. As the global commitment to sustainably manage ocean ecosystems and resources rises, there is a growing need to describe biodiversity trends in previously unsampled areas. Benthic invertebrate research in South Africa is a developing field, and many taxa in deep water environments remain inadequately characterized. Recently, the South African azooxanthellate scleractinian fauna was taxonomically reviewed, but their distributional correlations with physical parameters have not been studied. Here we aim to understand the biodiversity gradients of the South African azooxanthellate coral fauna by analysing the environmental correlates of museum samples. The associated coordinate data were georeferenced and depth obtained from a national bathymetric dataset, prior to undertaking a multivariate analysis. This analysis encompassed several steps, including the grouping of the longitude and depth data (environmental data), identifying families characteristic of the group variability, and examining the correlation of the associated data with the biological data. Additionally, the analysis involved quantifying diversity patterns along the environmental gradients. Overall, our results confirmed two longitudinal groups (eastern margin [Group A] vs southern and western margin [Group B]) and 11 depth categories represented within two bathymetric zones (shallow [50-200 m] and deep [300-1000 m]). Caryophylliids, flabellids, and dendrophylliids contributed the most towards distinguishing longitudinal and depth gradients. Both abiotic variable (longitudinal and depth) partially explained coral distribution patterns, with depth being highly correlated to the species variation observed. Data limitations within our data set resulted to unexplained variance, however, despite these limitations, the study demonstrates that historical museum samples provide a valuable data source that can fill research sampling gaps and help improve the understanding of biodiversity patterns of the coral fauna in under sampled marine ecosystems.

Dimorphic life cycle through transverse division in burrowing hard coral Deltocyathoides orientalis

The azooxanthellate solitary scleractinian Deltocyathoides orientalis (family Turbinoliidae), which has bowl-shaped costate corallites, exhibits burrowing behavior on soft substrates and can adapt to an infaunal mode of life. Here, we describe previously unknown aspects of their life history and asexual mode of reproduction based on morphological and molecular phylogenetic analyses. The findings reveal that (1) D. orientalis exhibits asexual reproduction by transverse division; (2) smaller bowl-shaped costate anthocyathus derived from cylindrical to tympanoid anthocaulus were attached to hard substrates, including shell fragments and gravels on soft substrates; and (3) anthocyathus only reproduce sexually after division, and anthocaulus was found to regrow and repeatedly produce anthocyathi through transverse division. The bowl-shaped corallum morphology of the anthocyathus just after division might reduce the time required for skeletal formation to enable infaunal adaption after transverse division. Immediately after division, D. orientalis can smoothly shift to a burrowing lifestyle that efficiently utilizes soft-substrate environments, thus increasing its survival rate. The morphological formation of prospective anthocyathus in the anthocaulus stage is consequently thought to involve an increase in clonal individuals as well as adaptations for a burrowing free-living mode of life in the anthocyathus stage.

New Records of Azooxanthellate Scleractinian Corals (Cnidaria: Anthozoa) from Sagami Bay and Suruga Bay, Japan.

Sagami Bay and Suruga Bay harbor a rich marine biodiversity; however, their outer-shelf scleractinian coral fauna has not been characterized to date. Scleractinian corals were collected by dredge sampling of the Japanese Association for Marine Biology (JAMBIO) Coastal Organisms Joint Surveys in 2015 to elucidate the diversity of azooxanthellate scleractinian corals from the outer shelf zones of Sagami Bay and Suruga Bay. In this study, a total of 1291 azooxanthellate scleractinian specimens were collected, corresponding to 23 genera and 18 species, five of which are new records for Sagami Bay and eight are new records for Suruga Bay. Moreover, in all localities, except sampling locality (SL) 8, more than 70% of the specimens showed asexual reproduction. This finding suggests that asexual reproduction may play an important role in increasing the coral population size in soft-substrate environments of the outer shelf.

A new species of azooxanthellate Scleractinia from the western Atlantic, and a new name and record of Desmophyllum striatum sensu Cairns, 1979

A new species of deep-water azooxanthellate scleractinian coral is described from the northwestern Atlantic, named Trochocyathus circularis. It is distinctive for its almost circular calice. A new name is proposed for the junior primary homonym Desmophyllum striatumCairns, 1979, which was preoccupied by the senior homonym, a Miocene fossil from Italy, described in 1871 by Sismonda in Sismonda & Michelotti.

Ocean acidification causes variable trait-shifts in a coral species.

High pCO2 habitats and their populations provide an unparalleled opportunity to assess how species may survive under future ocean acidification conditions, and help to reveal the traits that confer tolerance. Here we utilize a unique CO2 vent system to study the effects of exposure to elevated pCO2 on trait-shifts observed throughout natural populations of Astroides calycularis, an azooxanthellate scleractinian coral endemic to the Mediterranean. Unexpected shifts in skeletal and growth patterns were found. Colonies shifted to a skeletal phenotype characterized by encrusting morphology, smaller size, reduced coenosarc tissue, fewer polyps, and less porous and denser skeletons at low pH. Interestingly, while individual polyps calcified more and extended faster at low pH, whole colonies found at low pH site calcified and extended their skeleton at the same rate as did those at ambient pH sites. Transcriptomic data revealed strong genetic differentiation among local populations of this warm water species whose distribution range is currently expanding northward. We found excess differentiation in the CO2 vent population for genes central to calcification, including genes for calcium management (calmodulin, calcium-binding proteins), pH regulation (V-type proton ATPase), and inorganic carbon regulation (carbonic anhydrase). Combined, our results demonstrate how coral populations can persist in high pCO2 environments, making this system a powerful candidate for investigating acclimatization and local adaptation of organisms to global environmental change.

Microskeletal Structures Suggest Taxonomic Distinction between Subgenera of Azooxanthellate Scleractinian Flabellum

Recent molecular analyses have challenged the traditional classification of scleractinian corals at almost all taxonomic levels, suggesting a requirement of new morphological characters for classification. Microskeletal characters have shown great potential to support the classification of the molecular-based clades of the scleractinian corals. Flabellum (Family Flabellidae) is the fifth largest genus and contains two subgenera, F. (Flabellum) and F. (Ulocyathus). The genus is very important in deciphering flabellid evolution, as phylogenetic relationship is still ambiguous in this family. In particular, little is known of the microstructural features of Flabellum species. Here we discuss the microskeletal structures of F. (F.) magnificum and F. (U.) deludens. Rapid accretion deposits (RADs) on the walls of F. (F.) magnificum show dome-shaped strands ca. 50–100 µm wide, which are composed alternatively of microcrystalline and fibrous parts. In contrast, the RADs on the walls of F. (U.) deludens consist of strands (50–100 µm long and 20–30 µm wide) made up of very short fibers (ca. 0.5–5 µm long) or microcrystallines with meniscus structure and dome-shaped fibrous layers. Thickening deposits (TDs) on the walls of both species are characterized by three qualities: (1) layered bundles consisting of fibrous crystals; (2) shingle-like TDs composed of small crystals and microcrystallines; and (3) shingle-like TDs comprised of larger fibers. In particular, in F. (U.) deludens, the TD of the calicular side of the wall is mainly formed of shingle-like TDs. The walls of F. (U.) deludens and F. (F.) magnificum thus differ completely in terms of the RAD (digitated strand and dome-shaped fibrous layers vs. continuous dome-shaped alternation) and TD characteristics. These kinds of microskeletal differences could support the molecular phylogenetic distinction between the F. (U.) spp. cluster and the F. (F.) clusters.

Microbiome of the Southwestern Atlantic invasive scleractinian coral, Tubastraea tagusensis

BackgroundCommonly known as sun-coral, Tubastraea tagusensis is an azooxanthellate scleractinian coral that successfully invaded the Southwestern Atlantic causing significant seascape changes. Today it is reported to over 3500 km along the Brazilian coast, with several rocky shores displaying high substrate coverage. Apart from its singular invasiveness capacity, the documentation and, therefore, understanding of the role of symbiotic microorganisms in the sun-coral invasion is still scarce. However, in general, the broad and constant relationship between corals and microorganisms led to the development of co-evolution hypotheses. As such, it has been shown that the microbial community responds to environmental factors, adjustment of the holobiont, adapting its microbiome, and improving the hosts’ fitness in a short space of time. Here we describe the microbial community (i.e. Bacteria) associated with sun-coral larvae and adult colonies from a locality displaying a high invasion development.ResultsThe usage of high throughput sequencing indicates a great diversity of Bacteria associated with T. tagusensis, with Cyanobacteria, Proteobacteria, Bacteroidetes, Actinobacteria, Planctomycetes, and Firmicutes corresponding to the majority of the microbiome in all samples. However, T. tagusensis’ microbial core consists of only eight genera for colonies, and, within them, three are also present in the sequenced larvae. Overall, the microbiome from colonies sampled at different depths did not show significant differences. The microbiome of the larvae suggests a partial vertical transfer of the microbial core in this species.ConclusionAlthough diverse, the microbiome core of adult Tubastraea tagusensis is composed of only eight genera, of which three are transferred from the mother colony to their larvae. The remaining bacteria genera are acquired from the seawater, indicating that they might play a role in the host fitness and, therefore, facilitate the sun-coral invasion in the Southwestern Atlantic.

The rise of a native sun coral species on southern Caribbean coral reefs

AbstractIn contrast with a general decline of Caribbean reef corals, a previously rare sun coral is increasing in abundance within shallow coral communities on Curaçao. This azooxanthellate scleractinian was identified as Cladopsammia manuelensis, which has an amphi‐Atlantic distribution. Over the last decade, C. manuelensis has increased abundance along the leeward coast of Curaçao (southern Caribbean) between depths of 4 and 30 m. This species was initially not noticed because it resembles the invasive coral Tubastraea coccinea, which was introduced to Curaçao from the Indo‐Pacific around 1940. However, in contrast to T. coccinea, C. manuelensis was previously only present on deeper reef sections (>70 m) of Caribbean reefs. Our observations illustrate how the sudden increase in abundance of a previously unnoticed, apparently cryptogenic species could result from natural dynamics on present‐day reefs, but also could easily be mistaken for an invasive species. The finding that deep reef sections can harbor species capable of colonizing shallower reef zones highlights the importance of thorough inventories of reef communities across large depth ranges, which can help us to discriminate between range increases of native species and the arrival of invasives.

A review of contemporary patterns of endemism for shallow water reef fauna in the Red Sea

AbstractAimThe Red Sea is characterised by a unique fauna and historical periods of desiccation, hypersalinity and intermittent isolation. The origin and contemporary composition of reef‐associated taxa in this region can illuminate biogeographical principles about vicariance and the establishment (or local extirpation) of existing species. Here we aim to: (1) outline the distribution of shallow water fauna between the Red Sea and adjacent regions, (2) explore mechanisms for maintaining these distributions and (3) propose hypotheses to test these mechanisms.LocationRed Sea, Gulf of Aden, Arabian Sea, Arabian Gulf and Indian Ocean.MethodsUpdated checklists for scleractinian corals, fishes and non‐coral invertebrates were used to determine species richness in the Red Sea and the rest of the Arabian Peninsula and assess levels of endemism. Fine‐scale diversity and abundance of reef fishes within the Red Sea were explored using ecological survey data.ResultsWithin the Red Sea, we recorded 346 zooxanthellate and azooxanthellate scleractinian coral species of which 19 are endemic (5.5%). Currently 635 species of polychaetes, 211 echinoderms and 79 ascidians have been documented, with endemism rates of 12.6%, 8.1% and 16.5% respectively. A preliminary compilation of 231 species of crustaceans and 137 species of molluscs include 10.0% and 6.6% endemism respectively. We documented 1071 shallow fish species, with 12.9% endemic in the entire Red Sea and 14.1% endemic in the Red Sea and Gulf of Aden. Based on ecological survey data of endemic fishes, there were no major changes in species richness or abundance across 1100 km of Saudi Arabian coastline.Main conclusionsThe Red Sea biota appears resilient to major environmental fluctuations and is characterized by high rates of endemism with variable degrees of incursion into the Gulf of Aden. The nearby Omani and Arabian Gulfs also have variable environments and high levels of endemism, but these are not consistently distinct across taxa. The presence of physical barriers does not appear to explain species distributions, which are more likely determined by ecological plasticity and genetic diversity.

Morphological Variability in Azooxanthellate Scleractinian Dendrophylliids Governed by Regular Modes of Asexual Reproduction: A Computer Simulation Approach

Abstract. Morphogenetic mechanisms in modern Scleractinia provide insights into the habitats and growth forms of corals living in different environmental conditions. Scleractinian morphogenesis has been studied primarily in relation to extrinsic (e.g. environmental) factors, irrespective of specific regularities in budding and their impacts on growth forms. Morphogenesis in colonial dendrophylliids can be modelled by taking these developmental traits into account, so as to understand how intrinsic developmental factors affect morphologies resulting from colonial growth. We used a simple, voxel-based program to simulate the morphogenesis of dendrophylliid corals. Three parameters (budding orientation, inclination of budding, and interval of budding) were adopted to simulate a range of colonial growth forms, regardless of whether the forms exist in nature or not. The regularity of budding was fully taken into account, and various colonial morphologies were gained, even under strict regularity. The regulatio...

Internal skeletal analysis of the colonial azooxanthellate scleractinian Dendrophyllia cribrosa using microfocus X-ray CT images: underlying basis for its rigid and highly adaptive colony structure.

Dendrophyllid Scleractinia exhibit a variety of colonial morphologies, formed under the strict constraints on (1) budding sites, (2) orientations of the directive septa of offsets, (3) inclination of budding direction, and (4) those constraints in every generation. Dendrophyllia cribrosa exhibits a sympodial dendroid form, characteristically large coralla, and occasional fusions of adjacent branches within the same colony. Adjacent corallites are bound and supported by coenosteum skeleton. This study examined the inner skeletal structures at the junctions of fused branches using a non-destructive microfocus X-ray computed tomography (CT) imaging approach, and considered the reasons for the large colonial sizes and their adaptive significance. Three-dimensional reconstructions of two-dimensional X-ray CT images reveal that individual corallites are not directly connected in fused parts. Additionally, no completely buried individuals were found within fused skeleton. When adjacent branches approach one another, constituent corallites change their growth directions to avoid collisions between the branches. The adjacent branches fuse without a reduction in the number of constituent corallites, leading to the establishment of reticular and rigid colonial structures. In addition, a nearly even distribution of individuals on the colony surface facilitates efficient intake of nutrients. Thus, the growth of large D. cribrosa colonies involves avoidance of collision between constituent individuals, the reinforcement of colonial structure, and efficient uptake of nutrients. These observations provide insights on the dynamics of interrelationships between colony-making mechanisms and the adaptive strategies required under habitat conditions such as specific current activities.

Comparison of metal accumulation in the azooxanthellate scleractinian coral (Tubastraea coccinea) from different polluted environments

The response of metal accumulation in coral Tubastraea coccinea to various degrees of metal enrichment was investigated from the Yin-Yang Sea (YYS) receiving abandoned mining effluents, the Kueishan Islet (KI) hydrothermal vent field, and the nearshore area of remoted Green Island (GI). The concentrations of most dissolved metals were highest in seawater at YYS, followed by KI, and then GI, showing the effects of anthropogenic and venting inputs on metal levels. Five metals (Co, Fe, Mn, Ni, and Zn) yielded significant differences (p<0.05) among the skeleton samples. We identified similar patterns in the metal–Ca ratios, indicating that the elevated metals in skeletons was a consequence of external inputs. The coral tissues were relatively sensitive in monitoring metal accumulation, showing significant differences among three locations for Cd, Co, Cu, Fe, Pb, Ni, and Zn. Specific bioconcentration factors provided strong support for the differential metal accumulation in skeletons and tissues.

Phenological and morphological variations in the Mediterranean orange coral Astroides calycularis between two distant localities

Studies of intraspecific variation in the presence of different environmental features are essential to improving the knowledge of species population dynamics and structure. Astroides calycularis is an azooxanthellate scleractinian coral commonly found in shallow rocky habitats of the southwestern Mediterranean Sea. This study compares the fertilization period of two coral populations located in distantly separated localities; one in an upwelling area off the southern coast of the Iberian Peninsula, and the other on the southwestern coasts of Italy. Colony morphology varied between localities, the former having massive-shaped morphology with densely crowded polyps, the latter having bush-shaped morphology and separated polyps. These differences are possibly due to the different hydrodynamic conditions of their respective habitats. Gonochorism and planula brooding as sexual patterns and conditions of the coral coincide at both sites, but a delay in the timing of fertilization and planulation of the southern Iberian Peninsula population was observed, probably linked to a shift in the time at which seawater reaches its maximum temperature at each site.

Growth and Demography of the Solitary Scleractinian Coral Leptopsammia pruvoti along a Sea Surface Temperature Gradient in the Mediterranean Sea

The demographic traits of the solitary azooxanthellate scleractinian Leptopsammia pruvoti were determined in six populations on a sea surface temperature (SST) gradient along the western Italian coasts. This is the first investigation of the growth and demography characteristics of an azooxanthellate scleractinian along a natural SST gradient. Growth rate was homogeneous across all populations, which spanned 7 degrees of latitude. Population age structures differed between populations, but none of the considered demographic parameters correlated with SST, indicating possible effects of local environmental conditions. Compared to another Mediterranean solitary scleractinian, Balanophyllia europaea, zooxanthellate and whose growth, demography and calcification have been studied in the same sites, L. pruvoti seems more tolerant to temperature increase. The higher tolerance of L. pruvoti, relative to B. europaea, may rely on the absence of symbionts, and thus the lack of an inhibition of host physiological processes by the heat-stressed zooxanthellae. However, the comparison between the two species must be taken cautiously, due to the likely temperature differences between the two sampling depths. Increasing research effort on determining the effects of temperature on the poorly studied azooxanthellate scleractinians may shed light on the possible species assemblage shifts that are likely to occur during the current century as a consequence of global climatic change.

Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula

Sentoku, A. & Ezaki, Y. 2011: Constraints on the formation of colonies of the extant azooxanthellate scleractinian coral Dendrophyllia arbuscula. Lethaia, Vol. 45, pp. 62–70. Scleractinia display a variety of growth forms, whether zooxanthellate or azooxanthellate, as the consequence of the combined effects of both intrinsic and extrinsic factors. New modules arise in colonial corals through asexual reproduction, including budding and division. The azooxanthellate, branching dendrophylliid Dendrophyllia arbusculavan der Horst 1922, is a good species to investigate intrinsic regularities in budding, because: (1) the lateral corallites always occur in the vicinity of four primary septa, excluding the two directive primary septa; (2) the two directive septa in lateral corallites tend to be oriented almost perpendicular to the growth orientation of parental corallites; (3) the lateral corallites grow more-or-less diagonally upwards; and (4) these regularities are retained from the axial to the derived lateral corallites during colony growth. Accordingly, a colony of apparently complex dendroid corals is formed according to certain universal rules that apply to successive generations of corallites. The presence of two opposite sectors in which budding do not occur seems to be common to other azooxanthellate scleractinian families. Regularities, other than the orientation of the directive septa, are also commonly found at least in other azooxanthellate dendrophylliid genera. These regularities suggest the presence of strict developmental constraints on the asexual reproduction of the Scleractinia, both extant and extinct. These regularities by azooxanthellate scleractinians, as one of the representative colonial metazoan groups, provide us with fundamental data with which we can understand how colonies are constructed. □Azooxanthellate coral, budding, colony, Dendrophyllia arbuscula, regularity.

Sexual Reproduction in the Mediterranean Endemic Orange Coral Astroides Calycularis (Scleractinia: Dendrophylliidae)

Astroides calycularis (Pallas, 1766) is a common endemic azooxanthellate scleractinian coral living in the southwestern Mediterranean Sea, generally in shaded habitats, below overhangs, or at cave entrances, from the surface to 50 m depth. The annual reproductive cycle of A. calycularis (gamete development in relation to environmental parameters, planulation timing, size at sexual maturity, fecundity, and sex ratio) was studied at Palinuro in the southern Tyrrhenian Sea (Italy) from April 2004 to September 2005. Colonies were gonochoric, were mature at 3-4 cm2 in area, and had a sex ratio of 1:1. Polyps were sexually mature at 3-4 mm length (maximum diameter of the oral disc), and the females brooded their larvae. The maturation of spermaries took 7 mo and that of oocytes took over 12 mo. The rate of gamete development increased significantly from November to March. Fertilization occurred from April to May, with planulation in June. Mature oocytes ranged from 400 to 1590 ?m and planulae size was 1850 ?m (oral-aboral axis). Seasonal variation in seawater temperature and photoperiod likely play an important role in regulating reproductive events. The amount of energy devoted to male gametogenesis (quantified by gamete index) was significantly higher than female gametogenesis. in relation to other dendrophylliids, A. calycularis presents an intermediate reproductive strategy on the r-K continuum.

Calcification rate and the effect of temperature in a zooxanthellate and an azooxanthellate scleractinian reef coral

Calcification rates, normalized to skeletal mass, in the zooxanthellate Galaxea fascicularis and the azooxanthellate Dendrophyllia sp. were similar over the whole temperature range of 18–29 °C. Calcification was measured by Ca45 incorporation in corals that were naturally acclimated to the prevailing seawater temperature. In both species maximum calcification rate occurred at about 25 °C and calcification rates can be fitted to a Gaussian distribution with respect to temperature. The similarity in temperature dependence of the zooxanthellate and azooxanthellate coral suggests that temperature affects some fundamental process of calcification that is independent of light effects. It is shown that two different populations of Galaxea fascicularis have distinctly different ratios of tissue protein to skeletal mass per polyp. This indicates that tissue protein may not be suitable for normalizing calcification rates in individual coral polyps, both within and between species. Intra- and interspecific comparisons of calcification rates may be better made on the basis of skeletal mass when polyps are similar in size and shape.

Deep-water coral banks: an example from the “Calcare di Mendicino” (Upper Miocene, Northern Calabria, Italy)

The “Calcare di Mendicino” is a mixed carbonatesiliciclastic informal unit of Miocene (Late Tortonian-Early Messinian age), that crops out extensively in the northwestern part of the Calabria. In the Scannelle quarry near Belsito (Cosenza), four stratigraphic sections were studied to define the sedimentological and paleoecological setting. The carbonate body records the development of a deep-water coral bank characterized by a low-diverse community of azooxanthellate scleractinian (Oculina andDendrophyllia) and stylasterine hydrozoans colonies. Two main stages of bioconstruction development can be distinguished: a thicket and a bank stage. Among the biostromal dwellers the more common are bryozoans, echinoids, benthic foraminifers, gastropods, and bivalves. A higher content of planktonic foraminifers occur in the thicket stage. The coral bank flourished within the aphotic zone, with deep currents loaded with nutrients and siliciclastic sediments.

Composition of lipids, fatty acids and sterols in Okinawan corals

A survey of lipid composition was made for 15 cnidarians from Okinawa, Japan. Eleven zooxanthellate scleractinian corals, an azooxanthellate scleractinian coral Tubastrea sp., a soft coral Lobophytum crassum, a hydroid coral Millepora murrayi and a sea anemone Boloceroides sp. were examined to elucidate the total lipid content, fatty acid composition for each lipid class and sterol composition. All specimens contained monoalkyldiacylglycerol which migrated between the triacylglycerols and esters on thin layer chromatography (TLC). Analysis by high performance thin layer chromatography (HPTLC) and Gas chromatography-mass spectrometry (GC-MS) revealed that these cnidarians were rich in wax ester and triacylglycerol, and that palmitic acid (16:0) was the most abundant fatty acid component of these lipid classes, followed by stearic (18:0) and oleic (18:1, n-9) acid in order of concentration. Of 11 sterols separated, four sterols were identified. It is suggested that sterol composition may be more useful for the biochemical classification of these cnidarians than fatty acid composition.

Constructional Azooxanthellate Coral Communities: An Overview with Implications for the Fossil Record

As evidenced by the success of zooxanthellate coral species today, symbiosis with algae confers great advantages to organisms inhabiting the reef environment. Although not as well known as their zooxanthellate counterparts, azooxanthellate coral communities, dominated by so-called corals, can and do build constructionalframework, harboring a variety of associated vertebrate and invertebrate fauna. As has long been noted, when it comes to reefs and constructional roles, zooxanthellate and azooxanthellate corals exhibit mutually exclusive relationships. This is traditionally explained in terms of competition. When zooxanthellate species are absent due to restrictive environmental conditions, azooxanthellate species may inhabit relatively shallow water, even building limited constructional framework. In some non-reef settings where zooxanthellate corals are not living under optimal conditions, azooxanthellate species can be found living alongside them. On the shallow-water reef as a rule, azooxanthellate corals are relegated to cryptic habitats not colonizable by the overwhelmingly dominant zooxanthellate species. A review of 16 well-documented examples of modern constructional azooxanthellate coral communities and their physical and biological characteristics reveals a wide variety of latitudinal and depth ranges, temperatures, species composition, thicknesses, and species diversity. In all major oceans, they are best developed in cold and relatively deep water, as deep as 1500 m, and from the equator to latitudes of over 70?. Besides having a predominantly coral composition, some deep-water, azooxanthellate coral communities with extensive constructional framework have unexpected faunal diversity and presumably also complex interactions. The paleobiogeography and evolution of some of these deeper-water, coral-dominated azooxanthellate communities, known to have inhabited atolls and oceanic seamounts, may have been influenced by plate tectonic seafloor movements. While we are becoming increasingly cognizant of Holocene examples, counterparts in the geologic record are much more poorly known. The apparent paucity of ancient analogs may stem from difficulties in their interpretation and recognition in the geologic record. Judging from the size, facies relationships, faunal content, and diversity of Holocene examples, ancient deep-water coral structures, when preserved in the rock record, could be easily misconstrued as features of shallow-water origin. More careful analysis of deep-water Holocene examples can greatly expand our awareness of ancient analogs. In some cases, depending on the amount and thickness of construction, they could hold potential as hydrocarbon reservoirs. Azooxanthellate scleractinian communities are common in today's oceans and examples of them extend back to the Middle Triassic period. Fossil examples, unfortunately, are rare and sporadic in stratigraphic distribution, with the most notable reports from the Tertiary. Our view of the relative abundance of ancient counterparts may be hampered by poor preservation and problems of recognition.