Lizard Island Research Articles

Habitat-related variation in reproductive endocrine condition in the coral reef damselfish Acanthochromis polyacanthus

Spiny damselfish Acanthochromis polyacanthus are brood protectors with no larval dispersal stage, with the result that characteristics of local populations are likely to reflect local habitat conditions. In order to assess the possible effect of habitat on reproductive characteristics, spiny damselfish were captured by divers in 1999 and 2001 from reefs around Lizard Island in the northern section of Australia’s Great Barrier Reef, chosen to represent a range of coral cover characteristics. Fish were bled underwater immediately after capture, then blood and fish were placed on ice at the end of the dive for transport to the laboratory where plasma was separated for subsequent measurement of testosterone (T) and 11-ketotestosterone (11KT) in males, and T and 17β-estradiol (E 2) in females. Ovaries from fish captured in 2001 were dispersed to isolate vitellogenic follicles, fecundity and follicle size were determined, then follicles were incubated in Leibowitz L15 medium alone or with human chorionic gonadotropin (hCG), to assess steroidogenic capacity. In 1999 there were significant site to site variations in plasma T and E 2 levels in females, and in 2001, in E 2 in females, and in T and 11KT in males. Highest hormone levels were recorded from sites of both low and high coral cover (a measure of presumptive habitat quality), but there was consistently low steroid production in fish from a site of high coral cover and fish density. An initial expectation that poor reproductive condition might be associated with degraded coral sites was not met. Vitellogenic follicles from fish captured in 2001 showed increased in vitro production of E 2 and to a lesser extent, T, with increasing follicle size, and this was further augmented by treatment with hCG. Comparison of regression slopes of log E 2 production versus follicle size showed that fish from sites where there were generally low levels of plasma steroids also had impaired in vitro steroidogenic capacity, and that this effect partially disappeared when follicles were stimulated with hCG. Reduced steroidogenic capacity was strongly associated with low fecundity, indicating that low in vitro and in vivo E 2 production were reflected in reduced reproductive capacity. As the effect was most consistent at a site where fish density (and subsequent competition for planktonic food) was high, it is suggested that nutritional status associated with habitat characteristics may regulate reproductive endocrine condition in spiny damselfish. It is clear that local factors other than coral cover can generate site variation in reproductive performance.

Holorchis gigas n. sp. (Digenea: Lepocreadiidae) from the yellow-striped sweet-lips Plectorhinchus chrysotaenia (Perciformes: Haemulidae) from Lizard Island, Great Barrier Reef, with observations on Aephnidiogenes major

Holorchis gigas n. sp. is described from the fish Plectorhinchus chrysotaenia off Lizard Island on the Great Barrier Reef. It grows to over 180mm and is, therefore, much larger than any previously described species. It also differs from other Holorchis spp. in combinations of a different cirrus-sac structure, widely separated testes, entire ovary, short post-testicular region and the vitellarium not reaching the ventral sucker. Aephnidiogenes major is reported from Diagramma labiosum off Lizard and Heron Islands and P. chrysotaenia, off Lizard Island. Measurements of A. major are given.

Exploiting mimicry: Prosorhynchoides thomasi n. sp. (Digenea: Bucephalidae) from the fang blenny genus Plagiotremus (Bleeker) (Blenniidae) from off Lizard Island on the Great Barrier Reef, Australia

Prosorhynchoides thomasi n. sp. (Digenea: Bucephalidae) is described from the intestine of the fang blennies, Plagiotremus tapeinosoma and P. rhinorhynchos (Blenniidae: Nemophini) from off Lizard Island, Great Barrier Reef, Australia. The new species is differentiated from other species of Prosorhynchoides Dollfus, 1929 that also have testes which are symmetrical or nearly symmetrical by the shape and direction of the caecum and the position of the ovary relative to the caecum. This is the first report of a new species, but the second report of adult bucephalids from Plagiotremus spp. Prosorhynchoides thomasi n. sp. likely exploits the habit of Plagiotremus spp. of mimicking cleaner wrasse (Labridae) behaviour and micropredation on ‘client’ fish. We have not encountered this species from other blennies or from other teleost families known to be infected with bucephalids from the Great Barrier Reef

Rainfordia opercularis, a liopropomin serranid (Teleostei: Serranidae: Epinephelinae): corroborative evidence from settlement-stage larvae

Rainfordia opercularis was described in 1923 from a single specimen taken in Edgecumbe Bay, Queensland, Australia. The species is rare in museum collections, and the larvae have not been described. In 1999, two settlement-stage larvae (20–21 mm in standard length) were collected in light traps set off Lizard Island, Great Barrier Reef, Queensland. The smaller of the two has one thin, flexible, extremely elongate dorsal-fin spine encased in a pigmented sheath. The larger specimen lacks an elongate dorsal-fin spine and exhibits caudal-fin pigment characteristic of adults. A combination of features in one or both of the settlement-stage larvae support the placement of Rainfordia in the epinepheline-serranid tribe Liopropomini: presence of an elongate, filamentous dorsal-fin spine serially associated with the first dorsal-fin pterygiophore; presence of a spine on the inner preopercular ridge; presence of dense pigment on the frontals; absence of an elongate spine at the angle of the preopercle; and absence of supraorbital spination.

Opportunistic hybridization between two congeneric tropical reef fish

[Extract] The wrasses Halichoeres margaritaceus and Halichoeres miniatus (family Labridae) are monandric protogynous hermaphrodites, where males are derived from females through post-maturational sex change. Under stable social conditions the male of each species guards several intraspecific females and mates exclusively with those females daily. However, when male H. miniatus were removed during behavioural experiments at Lizard Island, Great Barrier Reef, male H. margaritaceus increased territory area to incorporate both H. margaritaceus and H. miniatus females. H. miniatus females participated in courting behaviour, resulting in pair-spawning bouts. When eggs from such spawnings were collected 79% were found to be fertilized, and these embryos hatched and develop into larvae. Hybrid spawning via the removal of H. miniatus males was replicated at two additional sites within the lagoon.

Two new species of Terebrasabella (Annelida: Sabellidae: Sabellinae) from Australia

Two new species of Terebrasabella Fitzhugh & Rouse, 1999 are described from eastern Australia. Terebrasabella hutchingsae sp. nov., was found from preserved coral rock debris collected in 1977 on the outer Barrier Reef near Lizard Island, Queensland. Terebrasabella fitzhughi sp. nov., was found alive in burrows in and among spirorbin serpulid tubes on intertidal rocks in Tasmania in 1996. Both species were found in mucoid tubes, and brood their young in a manner similar to the only other described species of Terebrasabella, T. heterouncinata Fitzhugh & Rouse, 1999. Terebrasabella hutchingsae sp. nov., is exceptional as it possesses a type of thoracic neurochaetal uncinus different from the other two species, and which is similar to the notochaetal acicular “palmate hook” seen in Caobangia. Descriptions of both species are given, and the diagnosis for Terebrasabella is emended. Larval and chaetal morphology and relationships among of the three known Terebrasabella spp. are discussed.

Monostephanostomum nolani sp. n. and M. krusei Reimer, 1983 (Digenea: Acanthocolpidae) from carangid fishes from coral reef waters off Australia

Monostephanostonum nolani sp. n. is described from Carangoides plagiotaenia Bleeker, off Lizard Island, Great Barrier Reef, Queensland, Australia. It differs from all other species in the genus except M. manteri Kruse, 1979 in that the vitellarium reaches into the forebody. It differs from M. manteri in the ventral hiatus in the circum-oral spine row, the extent of the vitellarium in the forebody, where it is not confluent, its elongate pharynx and its smaller eggs. Monostephanostoinum krusei Reimer, 1983 is redescribed from Pseudocaranx dentex (Bloch et Schneider) from Ningaloo Reef off Western Australia. It is considered similar to M. nolani, differing in the vitellarium being restricted to the hindbody, but sharing with M. nolani an unusual arrangement of small body-spines on the antero-ventral surface. It is also morphologically very similar to Monostephanostomum roytmani (Parukhin, 1974), which apparently lacks the diminutive antero-ventral body-spines. A key to eight recognized species in the genus is presented.

STRUCTURE OF THE PARASITE COMMUNITIES OF A CORAL REEF FISH ASSEMBLAGE (LABRIDAE): TESTING ECOLOGICAL AND PHYLOGENETIC HOST FACTORS

The role of ecological and phylogenetic processes is fundamental to understanding how parasite communities are structured. However, for coral reef fishes, such information is almost nonexistent. In this study, we analyzed the structure of the parasite communities based on composition, richness, abundance, and biovolume of ecto- and endoparasites of 14 wrasse species (Labridae) from Lizard Island, Great Barrier Reef, Australia. We determine whether the structure of the parasite communities from these fishes was related to ecological characteristics (body size, abundance, swimming ability, and diet) and/or the phylogenetic relatedness of the hosts. We examined 264 fishes from which almost 37,000 individual parasites and 98 parasite categories (types and species) were recorded. Gnathiid and cestode larvae were the most prevalent and abundant parasites in most fishes. Mean richness, abundance, and biovolume of ectoparasites per fish species were positively correlated with host body size only after controlling for the host phylogeny, whereas no such correlation was found for endoparasites with any host variable. Because most ectoparasites have direct transmission, one possible explanation for this pattern is that increased space (host body size) may increase the colonization and recruitment of ectoparasites. However, endoparasites generally have indirect transmission that can be affected by many other variables, such as number of prey infected and rate of parasite transmission.

Host specificity of two species of Gnathia (Isopoda) determined by DNA sequencing blood meals

Host specificity data for gnathiid isopods are scarce because the parasitic stages are difficult to identify and host-parasite contact is often brief. We examined two common nocturnal species, Gnathia falcipenis and Gnathia sp. C, collected in light traps from two locations at Lizard Island on the Great Barrier Reef, Australia. Engorged third stage gnathiids were photographed and permitted to moult into adults to allow identification. We compared ∼580bp sequences of 16S mtDNA from blood meals with host sequences available on GenBank using BLASTn. Where homology was <98%, familial identity was investigated with neighbour-joining trees. All blood meal sequences (n=60) and homologous fish sequences (n=87) from GenBank were used in a Bayesian analysis, which identified all but three sequences to family. The host frequency distributions used by each species were significantly different; only four host families were shared. No gnathiids fed on elasmobranchs, blennies or apogonids, and most fed on host families whose representatives are typically large. Gnathia sp. C showed a distinct predilection for nemipterids. Gnathia falcipenis often parasitised sand-dwelling families, and unlike sympatric diurnal gnathiid species, it also frequently parasitised pomacentrids. We conclude that G. falcipenis and Gnathia sp. C operate as generalist micropredators with preferences.

Elevated temperature and light enhance progression and spread of black band disease on staghorn corals of the Great Barrier Reef

Rates of progression and transmission of black band disease (BBD) on the staghorn coral, Acropora muricata, were compared between months for seasonal in situ studies and between temperature treatments in experimental aquaria manipulations at Lizard Island on the Great Barrier Reef (GBR). In situ field experiments demonstrated that BBD progressed along branches approximately twice as fast (1.7–2.4 times) during the austral summer month of January (0.99 ± 0.04 cm/day) than in the cooler months of July (0.58 ± 0.04 cm/day) and May (0.41 ± 0.07 cm/day). Transmission of BBD between colonies was also accelerated in warmer months, with signs of infection becoming visible 1.2 days earlier in January compared to May. The greater seawater temperatures by ∼2 to 3°C and light intensities by up to 650 μE/m2/s in January, suggest that rates of progression and transmission of BBD are linked to one or both of these parameters. Manipulative experiments in summer provide corroborative evidence that elevated temperatures increase rates of BBD progression, with the disease progressing 1.3 times more rapidly in the 32°C elevated temperature treatment than in the 30°C ambient treatment (1.17 ± 0.06 cm/day versus 0.92 ± 0.07 cm/day; F2,6 = 7.66, P = 0.022). In contrast, although a trend for greatest BBD progression was measured in elevated temperature treatments of 29°C (0.46 ± 0.07 cm/day) and 31°C (0.52 ± 0.06 cm/day) in winter, these rates did not differ significantly (F3,7 = 1.72, P = 0.249) from those measured for the ambient 27°C treatment (0.37 ± 0.06 cm/day) or the field controls (0.41 ± 0.09 cm/day). The lower rates of BBD progression in the 31°C winter treatment (0.52 ± 0.06 cm/day) than in the 30°C (0.92 ± 0.07 cm/day) summer treatment, may have been a response to 28-fold decreased light irradiance in the former, suggesting that high irradiance in combination with elevated temperatures may promote progression of BBD. Results from this study indicate that the impact of elevated temperature on BBD progression is complex with a combination of environmental factors including temperature and light playing key roles in progression and transmission of the disease.

Two new cryptogonimid genera (Digenea, Cryptogonimidae) from Lutjanus bohar (Perciformes, Lutjanidae): analyses of ribosomal DNA reveals wide geographic distribution and presence of cryptic species

AbstractWe describe three new species of Cryptogonimidae belonging to two new genera, Caulanus gen. nov. and Latuterus gen. nov., from the large piscivorous reef fish Lutjanus bohar Forsskål, 1775, recovered from Heron and Lizard Islands off the Great Barrier Reef and Rasdhoo Atoll, Maldives. To support our morphologically based taxonomic approach, three nuclear ribosomal DNA regions (28S, ITS1 and ITS2) were sequenced and analysed to explore the geographic distribution and integrity of the putative species recovered from these widespread localities. Sequencing of the rDNA regions included multiple replicates and revealed three distinct genotypes. Two of the observed genotypes were associated with phenotypically similar specimens of Latuterus, but were each restricted to a single locality, Lizard Island, GBR or Rasdhoo Atoll, Maldives. A posteriori analysis of the associated morphotypes revealed distinct morphological differences and these consistent differences, in combination with the consistent genetic differences led to the recognition of two distinct species in the system. Caulanus is distinguished by having oral spines, caeca which open via ani at the posterior end of the body, tandem testes and uterus that extends from the posterior end of the body to the pharynx. Latuterus is distinguished by lacking oral spines, having multiple/follicular testes, a uterus that is extensive in both fore-and hindbody and vitelline follicles which are confined to the region from the pharynx to oral sucker. Caulanus thomasi sp. nov. had identical sequences for all of the rDNA regions examined from specimens recovered from all three localities, indicating that this species has a wide Indo-Pacific distribution. The species reported here are evidently restricted to Lutjanus bohar because they were never found in large numbers of other lutjanid species sampled at the same localities.

A new species of Stephanostomum Looss, 1899 (Digenea, Acanthocolpidae) with a bizarre oral sucker: S. adlardi sp. nov. from the common coral trout Plectropomus leopardus (Lacepède, 1802) (Perciformes, Serranidae) from Lizard Island, Great Barrier Reef

AbstractA new species of Acanthocolpidae, Stephanostomum adlardi is described from the serranid Plectropomus leopardus from Lizard Island in the northern Great Barrier Reef. It differs from all previously described acanthocolpids in the structure of the oral sucker which is extended into dorsal and ventral lobes each bearing a row of spines. A phylogenetic tree estimated from combined nuclear small and partial large ribosomal RNA gene sequences shows that, despite the unusual oral sucker structure, the species is a true member of the genus Stephanostomum. The molecular results also suggest that Monostephanostomum nolani is derived from within Stephanostomum.

Cover Picture: Structure‐Based Organic Synthesis of Drug Prototypes: A Personal Odyssey (ChemMedChem 12/2006)

The cover picture shows the cyanobacterial linear peptides dysinosin A (RH) and chlorodysinosin A (RCl), members of the aeruginosin family of cyanobacterial linear peptides. Their structures and absolute configurations were determined by total synthesis and X‐ray co‐crystallization with the enzyme thrombin. The presence of one chlorine atom in the D‐leucine residue of chlorodysinosin A remarkably increases the inhibition potency against thrombin and Factor VIIa relative to dysinosin A. Molecular mechanics simulations starting from the bound conformations of dysinosin A and its chloro analogue suggest a more restricted sampling of conformations for the latter around the χ1 dihedral angle. The chlorine atom in chlorodysinosin A may also contribute to lipophilicity, leading to a better fit in the hydrophobic S3 pocket, as illustrated in the partial X‐ray co‐crystal structure. The background of the picture shows Lizard Island in North Queensland, Australia, where dysinosin A was isolated from the Dysideidae family of marine sponges. For details, see the Review by S. Hanessian on p. 1300 ff.

Uncommon diversity in developmental mode and larval form in the genus Macrophiothrix (Echinodermata: Ophiuroidea)

Development mode in the ophiuroid genus Macrophiothrix includes an unusual diversity of plank- tonic larval forms and feeding types. The modes of development for seven congeners that coexist in coral reef habitats at Lizard Island, Australia were com- pared using larvae generated from crosses over several reproductive seasons from 1999 to 2003. Three species (Macrophiothrix koehleri Clark, Macrophiothrix longi- peda Lamarck, Macrophiothrix lorioli Clark) develop from small eggs (<170 m) into typical obligately feed- ing planktonic (planktotrophic) pluteus larvae with four larval arm pairs. The remaining four species develop from larger eggs (¸230 m) into either faculta- tively-feeding or non-feeding (lecithotrophic) larval forms. The facultative planktotroph (Macrophiothrix rhabdota Clark) retains the ability to digest and beneWt from food but does not require particulate food to complete metamorphosis. Among the lecithotrophic species, Macrophiothrix caenosa Hoggett retains the pluteus morphology with four pairs of larval arms, but is incapable of feeding, depending instead on maternal provisions for larval development. The remaining two lecithotrophs have simpliWed larval morphologies with only a single pair of full length (Macrophiothrix nerei- dina Lamarck) or highly reduced (Macrophiothrix belli Doderlein) larval arms and no functional mouth or gut. This genus includes the Wrst example of facultative planktotrophy in ophiuroids, the Wrst example in echi- noderms of a complete pluteus morphology retained by a lecithotrophic larva, and three degrees of morpho- logical simpliWcation among lecithotrophic larval forms. Egg volume varies 20-fold among species and is related to variation in feeding mode, larval form, and development time, as predicted for the transition from planktotrophic to lecithotrophic development.

Three new ostracod species from coastal Australian waters (Crustacea: Ostracoda: Myodocopa: Cylindroleberididae)

Three new species of Cylindroleberididae are described: Parasterope gamurru from Lizard Island (Queensland), Diasterope wirraka from Bass Strait (Victoria), and Cylindroleberis marranyin from Sandy Point (Victoria). This is the first record of species of Cylindroleberis and Diasterope from Australia, and the first record of a species of Parasterope from Queensland. Juvenile instars of species of Cylindroleberis are compared in order to assign appropriate stages to those of Cylindroleberis marranyin.

Holocene evolution of the granite based Lizard Island and MacGillivray Reef systems, Northern Great Barrier Reef

Radiocarbon dating of seven drill cores from both the windward Lizard Island fringing reef and the windward and leeward margins of MacGillivray platform reef, Northern Great Barrier Reef Province, reveal the Holocene evolution of these two mid shelf coral reefs. The windward margin at Lizard Island started growing approximately 6,700 calendar years before present (cal yr BP) directly on an assumed granite basement and approached present day sea level approximately 4,000 cal yr BP. Growth of the windward margin at MacGillivray Reef was initiated by 7,600 cal yr BP and approached present day sea level by approximately 5,600 cal yr BP. The leeward margin at MacGillivray was initiated by 8,200 cal yr BP also directly on an assumed granite basement, but only approached sea level relatively recently, between 260 and 80 cal yr BP. None of the cores penetrated the Holocene-Pleistocene unconformity. The absence of Pleistocene reefal deposits, at 15 m depth in the cores from MacGillivray Reef, raises the possibility that the shelf in this region has subsided relative to modern day sea level by at least 15 m since the last interglacial [125,000 years ago (ka)].

HEMATOZOA OF TELEOSTS FROM LIZARD ISLAND, AUSTRALIA, WITH SOME COMMENTS ON THEIR POSSIBLE MODE OF TRANSMISSION AND THE DESCRIPTION OF A NEW HEMOGREGARINE SPECIES

Little is known of the blood parasites of coral reef fishes and nothing of how they are transmitted. We examined 497 fishes from 22 families, 47 genera, and 78 species captured at Lizard Island, Australia, between May 1997 and April 2003 for hematozoa and ectoparasites. We also investigated whether gnathiid isopods might serve as potential vectors of fish hemogregarines. Fifty-eight of 124 fishes caught in March 2002 had larval gnathiid isopods, up to 80 per host fish, and these were identified experimentally to be of 2 types, Gnathia sp. A and Gnathia sp. B. Caligid copepods were also recorded but no leeches. Hematozoa, found in 68 teleosts, were broadly hemogregarines of 4 types and an infection resembling Haemohormidium. Mixed infections (hemogregarine with Haemohormidium) were also observed, but no trypanosomes were detected in blood films. The hemogregarines were identified as Haemogregarina balistapi n. sp., Haemogregarina tetraodontis, possibly Haemogregarina bigemina, and an intraleukocytic hemogregarine of uncertain status. Laboratory-reared Gnathia sp. A larvae, fed experimentally on brushtail tangs, the latter heavily infected with the H. bigemina-like hemogregarine, contained hemogregarine gamonts and possibly young oocysts up to 3 days postfeeding, but no firm evidence that gnathiids transmit hemogregarines at Lizard Island was obtained.

Variation in emergence of parasitic and predatory isopods among habitats at Lizard Island, Great Barrier Reef

Gnathiid isopods are one of the most abun- dant groups of ectoparasites on coral reef Wshes. They, and other isopods, have been shown to signiWcantly aVect the health and behaviour of many reef Wsh. Whether isopod emergence diVers among habitats on coral reefs is not known. In this study, we measured emergence rates of parasitic isopods (Gnathiidea and Flabellifera) in six habitats at two sites at Lizard Island during new moon periods in March and December 2004. Isopods were collected from the periphery and centres of micro-reefs, patch reefs, continuous reefs, and from inter-reefal habitats (sand or rubble) with 1m 2 emergence traps. Sites (Casuarina and Coconut Beach) were located on opposite sides of Lizard Island. Live gnathiids were collected with light traps in Novem- ber 2005 to investigate species diVerences between sites. At both sites, the most abundant gnathiid species was exclusive to that site. More gnathiid larvae emerged at night, and emergence of fed gnathiids (pranizae) and Xabelliferan isopods was almost exclusively nocturnal. Diurnal emergence was greater at Coconut Beach than Casuarina Beach. Although emergence counts were not consistently aVected by parameters such as habitat, site, or sampling period, gnathiid size and feeding state were. Where signiWcant diVerences existed, gnathiids were larger and more often fed over reef borders than centrally. We suggest Wrst stage larvae (Z1) have the largest inXuence on total abundance and are patchily distributed in accordance with adults from which they have recently hatched. As later stage larvae depend on Wsh, more successful (fed) and older larvae are found on the edges of reefs where appropriate hosts may be more abundant, or predation is lower. Gnathiids were over- dispersed in all habitats investigated, including appar- ently homogeneous beds of coral rubble and sand. This indicates that their distributions may be better pre- dicted by very Wne scale diVerences in substrate or that aggregations are the result of gregariousness and may be diYcult to predict on the basis of substrate. Emer- gence traps collected comparatively few parasitic Xabel- liferan isopods. This community diVered greatly from the previously described community of scavenging iso- pods at Lizard Island. These diVerences are probably the result of diVerences in trapping methodology.

Location influences size-selective predation on newly settled reef fish

Demersal fish usually settle to established fish assemblages that include suites of gape-limited predators, whose compositions vary among locations. We investigated the extent to which predation was size-selective on a species of newly settled coral reef fish, the damselfish Pomacentrus amboinensis (Bleeker 1868), among 3 lagoonal sites on 1 reef. The 3 sites at Lizard Island, Great Barrier Reef, Australia, differed in species composition and relative abundance of predators. Fish at the end of their larval phase were caught in light traps and tattooed for individual recognition. They were then paired so that there was a 1 mm difference between partners, and placed on small patch reefs at the base of the 3 shallow lagoonal sites. Large individuals survived significantly better than small individuals in 1 out of 3 sites. One site displayed the reverse trend, even though non-significant, and the third site showed no evidence of selection. Selection was strongest at the site where predators of small reef fishes were in highest densities and water currents were strongest. Strong water currents appeared to emphasise size-related differences in swimming ability and increase the vulnerability of small fish at this site. Our results suggested that the occurrence of size-selection for this species at settlement will depend on the composition of the predator assemblage and prevailing environmental conditions; these both interact with the performance attributes of prey, and all 3 variables may be location-specific.

Cardicola Short, 1953 and Braya n. gen. (Digenea: Sanguinicolidae) from five families of tropical Indo-Pacific fishes

A survey of Pacific coral reef fishes for sanguinicolids revealed that two species of Lutjanidae (Lutjanus argentimaculatus, L. bohar), six species of Siganidae (Siganus corallinus, S. fuscescens, S. lineatus, S. margaritiferus, S. punctatus, S. vulpinus), seven species of Chaetodontidae (Chaetodon aureofasciatus, C. citrinellus, C. flavirostris, C. lineolatus, C. reticulatus, C. ulietensis, C. unimaculatus), three species of Scombridae (Euthynnus affinis, Scomberomorus commerson, S. munroi) and three species of Scaridae (Chlorurus microrhinos, Scarus frenatus, S. ghobban) were infected with morphologically similar sanguinicolids. These flukes have a flat elliptical body, a vestigial oral sucker, a single testis, separate genital pores and a post-ovarian uterus. However, these species clearly belong in two genera based on the position of the testis and genital pores. Sanguinicolids from Lutjanidae, Siganidae, Chaetodontidae and Scombridae belong in Cardicola Short, 1953; the testis originates anteriorly to, or at the anterior end of, the intercaecal field and does not extend posteriorly to it, the male genital pore opens laterally to the sinistral lateral nerve chord and the female pore opens near the level of the oötype (may be anterior, lateral or posterior to it) antero-dextral to the male pore. Those from Scaridae are placed in a new genus, Braya; the testis originates near the posterior end of the intercaecal field and extends posteriorly to it, the male pore opens medially at the posterior end of the body and the female pore opens posterior to the oötype, antero-sinistral to the male pore. The second internal transcribed spacer (ITS2) of ribosomal DNA from these sanguinicolids and a known species, Cardicola forsteri Cribb, Daintith &amp; Munday, 2000, were sequenced, aligned and analysed to test the distinctness of the putative new species. Results from morphological comparisons and molecular analyses suggest the presence of 18 putative species; 11 are described on the basis of combined morphological and molecular data and seven are not because they are characterised solely by molecular sequences or to few morphological specimens (n=one). There was usually a correlation between levels of morphological and genetic distinction in that pairs of species with the greatest genetic separation were also the least morphologically similar. The exception in this regard was the combination of Cardicola tantabiddii n. sp. from S. fuscescens from Ningaloo Reef (Western Australia) and Cardicola sp. 2 from the same host from Heron Island (Great Barrier Reef). These two parasite/host/location combinations had identical ITS2 sequences but appeared to differ morphologically (however, this could simply be due to a lack of morphological material for Cardicola sp. 2). Only one putative species (Cardicola sp. 1) was found in more than one location; most host species harboured distinct species in each geographical location surveyed (for example, S. corallinus from Heron and Lizard Islands) and some (for example, S. punctatus, S. fuscescens and Chlorurus microrhinos) harboured two species at a single location. Distance analysis of ITS2 showed that nine species from siganids, three from scombrids and five from scarids formed monophyletic clades to the exclusion of sanguinicolids from the other host families. Cardicola milleri n. sp. and C. chaetodontis Yamaguti, 1970 from lutjanids and chaetodontids, respectively, were the only representatives from those families that were sequenced. Within the clade formed by sanguinicolids from Siganidae there was a further division of species; species from the morphologically similar S. fuscescens and S. margaritiferus formed a monophyletic group to the exclusion of sanguinicolids from all other siganid species.