Ultrastructural comparison of Bonamia spp. (Haplosporidia) infecting ostreid oysters

The ultrastructure of Bonamia from Ostrea angasi from Australia, Crassostrea ariakensis from the USA, O. puelchana from Argentina and O. edulis from Spain was compared with described Bonamia spp. All appear conspecific with B. exitiosa. The Bonamia sp. from Chile had similarities to the type B. exitiosa from New Zealand (NZ), but less so than the other forms recognized as B. exitiosa. Two groups of ultrastructural features were identified; those associated with metabolism (mitochondrial profiles, lipid droplets and endoplasmic reticulum), and those associated with haplosporogenesis (Golgi, indentations in the nuclear surface, the putative trans-Golgi network, perinuclear granular material and haplosporosome-like bodies). Metabolic features were regarded as having little taxonomic value, and as the process of haplosporogenesis is not understood, only haplosporosome shape and size may be of taxonomic value. However, the uni-nucleate stages of spore-forming haplosporidians are poorly known and may be confused with Bonamia spp. uni-nucleate stages. The many forms of NZ B. exitiosa have not been observed in other hosts, which may indicate that it has a plastic life cycle. Although there are similarities between NZ B. exitiosa and Chilean Bonamia in the development of a larger uni-nucleate stage and the occurrence of cylindrical confronting cisternae, the clarification of the identity of Chilean Bonamia must await molecular studies.

Bonamia exitiosa transmission among, and incidence in, Asian oyster Crassostrea ariakensis under warm euhaline conditions

Previously reported in Australia, New Zealand, and more recently in Europe, the protistan parasite Bonamia exitiosa was also reported in the mid-Atlantic region of the USA after causing serious mortalities there in the Asian oyster Crassostrea ariakensis. At the time, this oyster was being considered for introduction, and the potential consequences of introducing this species were being assessed using field and laboratory studies. B. exitiosa emerged as the most serious disease threat for this oyster species, especially under warm euhaline conditions and for oysters <50 mm in size. To better evaluate how quickly this parasite may be able to spread among C. ariakensis, we investigated B. exitiosa transmission and incidence in C. ariakensis. During a first trial, potential direct transmission of B. exitiosa was evaluated by cohabitating infected C. ariakensis with uninfected C. ariakensis under in vivo quarantine conditions. In a second experiment, B. exitiosa incidence was estimated in situ by determining its prevalence in C. ariakensis deployed in an enzootic area after 4, 7, 14, 21 and 28 d of exposure. Results suggest that under warm euhaline conditions B. exitiosa can be transmitted among C. ariakensis without requiring any other parasite source and that parasite incidence may be at least as high as 40% after only 4 d exposure to an enzootic area. These results underscored the severity of the bonamiasis disease threat to C. ariakensis and provided further evidence that efforts to build an aquaculture industry based on C. ariakensis in the eastern USA might have been thwarted by parasitic disease.

Leeches on mudskippers: host-parasite interaction at the water's edge

A host-parasite relationship was observed, for the first time, between a piscicolid leech and a species of amphibious goby (Scartelaos tenuis) from an intertidal mud flat in southern Iran. Morphological and molecular investigations assign the leech to Zeylanicobdella arugamensis. Of the 3 endemic and sympatric mudskipper species living in the Persian Gulf (S. tenuis, Boleophthalmus dussumieri, and Periophthalmus waltoni), leeches were only found on S. tenuis (prevalence and mean intensity = 71.4% and 2.3 +/- 2.5, respectively), which is also the most-aquatic mudskipper species. Scartelaos tenuis is not the largest species, but more leeches (> or =4 leeches/host) were found on larger specimens (>12 cm standard length [SL]). Nonetheless, in aquaria, leeches also attached on P. waltoni. This suggests either an ecological partitioning of host-parasite complexes, determined by host habitat selection, or leech limited-resistance to air exposure, or both.

Inter-relationships of haplosporidians deduced from ultrastructural studies

We reviewed papers reporting haplosporidian ultrastructure to compare inter-relationships based on ultrastructure with those based on molecular data, to identify features that may be important in haplosporidian taxonomy, and to consider parasite taxonomy in relation to host taxonomy. There were links between the following: (1) the plasmodia of an abalone parasite, Haplosporidium nelsoni and Urosporidium crescens in the release of haplosporosomes; (2) H. costale and H. armoricanum in haplosporosome shape and presence and shape of Golgi in spores; (3) basal asporous crustacean haplosporidians which form haplosporosomes from formative bodies (FBs) in vegetative stages--H. nelsoni, which forms haplosporosomes from FBs in plasmodial cytoplasm, and H. louisiana, Minchinia spp. and Bonamia perspora, which form haplosporosomes from FBs in spores; (4) crustacean haplosporidians, Bonamia spp. and M. occulta in the predominance of uni- and binucleate stages; and (5) lipid-like vesicles in sporoplasms of H. costale, H. armoricanum, H. lusitanicum, H. pickfordi, H. montforti, and B. perspora. In general, these relationships reflect phylogenies based on molecular studies. As well as spore form and ornamentation, haplosporogenesis in spores appears to be taxonomically important. Parasite and host taxonomy were linked in the infection of lower invertebrates by Urosporidium spp., the infection of oysters by Bonamia spp., and of molluscs by Minchinia spp. Haplosporidium spp. are patently an artificial, paraphyletic group probably comprising many taxa. Consequently, the taxonomy of haplosporidians needs a thorough revision.

Shellfish tissues evaluated for Perkinsus spp. using the Ray's fluid thioglycollate medium culture assay can be used for downstream molecular assays

Ray's fluid thioglycollate medium (RFTM) culture assay is the standard, recommended method for surveillance of Perkinsus spp. infections in marine molluscs. In this assay, shellfish tissues are incubated in RFTM, stained with Lugol's iodine solution to render Perkinsus spp. cells blue-black, and evaluated microscopically to rate infection intensities. A limitation of this assay, however, is the lack of pathogen species specificity. Generally, identification of Perkinsus spp. requires DNA sequence analysis of parallel or additional samples since the exposure to iodine is believed to hamper DNA amplification from samples processed by the RFTM assay. However, we show that P. marinus DNA can be successfully amplified by PCR from Crassostrea virginica tissues cultured in RFTM and stained with Lugol's iodine. The beneficial consequence is that, where necessary, DNA sequence data may be obtained from RFTM-cultured tissues, allowing the identification of the Perkinsus sp. responsible for an observed infection. This would obviate further sampling, representing gain of time and reduction in cost, where a Perkinsus sp. is unexpectedly observed in new host(s) or location(s) but where parallel samples are not available for molecular diagnostics. Laboratories without molecular diagnostic tools for Perkinsus spp. may fix presumptive Perkinsus sp.-positive culture material in 95% ethanol for transport to, and subsequent analysis by, a laboratory that does have this capacity.

Pathogens in Crassostrea ariakensis and other Asian oyster species: implications for non-native oyster introduction to Chesapeake Bay

With the drastic decline of eastern oyster Crassostrea virginica populations in the Chesapeake Bay due to over-fishing, diseases and habitat destruction, there is interest in Maryland and Virginia in utilizing the non-native oyster species Crassostrea ariakensis for aquaculture, fishery resource enhancement, and ecological restoration. The International Council for the Exploration of the Sea (ICES) recommends that non-native species be examined for ecological, genetic and disease relationships in the native range prior to a deliberate introduction to a new region. Therefore, a pathogen survey of C. ariakensis and other sympatric oyster species was conducted on samples collected in the PR China, Japan and Korea using molecular diagnostics and histopathology. Molecular assays focused on 2 types of pathogens: protistan parasites in the genus Perkinsus and herpesviruses, both with known impacts on commercially important molluscan species around the world, including Asia. PCR amplification and DNA sequence data from the internal transcribed spacer region of the rRNA gene complex revealed the presence of 2 Perkinsus species not currently found in USA waters: P. olseni and an undescribed species. In addition, 3 genetic strains of molluscan herpesviruses were detected in oysters from several potential C. ariakensis broodstock acquisition sites in Asia. Viral gametocytic hypertrophy, Chlamydia-like organisms, a Steinhausia-like microsporidian, Perkinsus sp., Nematopsis sp., ciliates, and cestodes were also detected by histopathology.

Real-time PCR investigation of parasite ecology: in situ determination of oyster parasite Perkinsus marinus transmission dynamics in lower Chesapeake Bay

Perkinsus marinus is a severe pathogen of the oyster Crassostrea virginica on the East Coast of the United States. Transmission dynamics of this parasite were investigated in situ for 2 consecutive years (May through October) at 2 lower Chesapeake Bay sites. Compared to previous studies where seasonal infection patterns in oysters were measured, this study also provided parasite water column abundance data measured using real-time PCR. As previously observed, salinity and temperature modulated parasite transmission dynamics. Using regression analysis, parasite prevalence, oyster mortalities and parasite water column abundance were significantly positively related to salinity. Perkinsus marinus weighted prevalence in wild oysters and parasite water column abundance both were significantly related to temperature, but the responses lagged 1 month behind temperature. Parasite water column abundance was the highest during August (up to 1,200 cells/l) and was significantly related to P. marinus weighted prevalence in wild oysters, and to wild oyster mortality suggesting that parasites are released in the environment via both moribund and live hosts (i.e. through feces). Incidence was not significantly related to parasite water column abundance, which seems to indicate the absence of a linear relationship or that infection acquisition is controlled by a more complex set of parameters.

Molecular diagnostics, field validation, and phylogenetic analysis of Quahog Parasite Unknown (QPX), a pathogen of the hard clam Mercenaria mercenaria

Quahog Parasite Unknown (QPX) is a protistan parasite that causes disease and mortality in the hard clam Mercenaria mercenaria. PCR primers and DNA oligonucleotide probes were designed and evaluated for sensitivity and specificity for the QPX organism specifically and for the phylum Labyrinthulomycota in general. The best performing QPX-specific primer pair amplified a 665 bp region of the QPX small-subunit ribosomal DNA (SSU rDNA) and detected as little as 1 fg cloned QPX SSU rDNA and 20 fg QPX genomic DNA. The primers did not amplify DNA of uninfected hard clams M. mercenaria or of the thraustochytrids Schizochytrium aggregatum, Thraustochytrium aureum, and T. striatum. The general labyrinthulomycete primers, which were designed to offer broader specificity than the QPX primers, amplified a 435 bp region of SSU rDNA from QPX, and a 436 to 437 bp region of SSU rDNA from S. aggregatum, T. aureum, and T. striatum, but did not amplify that of the clam M. mercenaria. Field validation of the QPX-specific primer pair, through comparative sampling of 224 clams collected over a 16 mo period from a QPX endemic site in Virginia, USA, indicated that the PCR assay is equivalent to histological diagnosis if initially negative PCR products are reamplified. Oligonucleotide DNA probes specific for QPX and the phylum Labyrinthulomycota were evaluated for in situ hybridization assays of cell smears or paraffin-embedded tissues. Two DNA probes for QPX offered limited sensitivity when used independently; however, when used together as a probe cocktail, sensitivity was greatly enhanced. The probe cocktail hybridized to putative QPX organisms in tissues of hard clams collected from Virginia, New Jersey, Massachusetts and Canada, suggesting that the QPX organisms in these areas are either very closely related or the same species. The QPX probe cocktail did not hybridize with clam tissue or with the thraustochytrids S. aggregatum, T. aureum, and T. striatum. The labyrinthulomycete DNA probe hybridized with QPX and the 3 thraustochytrids, with no background hybridization to clam tissue. SSU rDNA sequences were obtained for the putative QPX organisms from geographically distinct sites. Phylogenetic analyses based on the QPX and Labyrinthulomycota sequences confirmed earlier reports that QPX is a member of this phylum, but could not definitively demonstrate that all of the QPX organisms were the same species.

Validating Livanow: molecular data agree that leeches, Branchiobdellidans, and Acanthobdella peledina form a monophyletic group of oligochaetes

To investigate the phylogenetic relationships of leeches, branchiobdellidans, and acanthobdellidans, whole nuclear 18S rDNA and over 650 bp of mitochondrial cytochrome c oxidase subunit I were acquired from 101 annelids, including 36 leeches, 18 branchiobdellidans, Acanthobdella peledina, as well as 28 oligochaetes and combined with homologous data for 17 polychaete outgroup taxa. Parsimony analysis of the combined aligned dataset supported monophyly of leeches, branchiobdellidans, and acanthobdellidans in 100% of jackknife replicates. Monophyly of the oligochaete order Lumbriculida with Acanthobdellida, Branchiobdellida, and Hirudinea was supported in 84% of jackknife replicates. These results provide support for the hypotheses that leeches and branchiobdellidans are sister groups, that acanthobdellidans are sister to them, and that together with the family Lumbriculidae they all constitute a clade within Oligochaeta. Results support synonymy of the classes Clitellata and the more commonly used Oligochaeta. Leeches branchiobdellidans, and acanthobdellidans should be regarded as orders equal to their closest relatives, the order Lumbriculida.

Spore ornamentation of Haplosporidium pickfordi Barrow, 1961 (Haplosporidia), a parasite of freshwater snails in Michigan, USA

Spore ornamentation is increasingly recognized as a key character for species differentiation and genus assignment in the phylum Haplosporidia. Unfortunately, spore ornamentation is known for only a small number of described species so it is difficult to assign most species to genera with any confidence. Scanning and transmission electron microscopy were used to determine the presence and morphology of spore ornamentation of Haplosporidium pickfordi collected from the digestive gland of the snail Physella parkeri in Douglas Lake, Michigan. Spores possess filaments that are derived from the spore wall and originate from two separate areas at the posterior end of the spore. When spores are first isolated from host tissue, filaments are fused into a sheet that wraps around the spore, passing under the opercular lid. These filaments gradually unravel when spores are held in water and after about 14 d most filaments project freely from the posterior end of the spore. The number of filaments could not be determined with certainty, but appears to be approximately nine. Filaments are 100 nm in diam. and up to 50 microm in length. The presence of spore wall-derived filaments confirms the placement of the parasite in the genus Haplosporidium.

Haplosporidiosis in the Pacific oyster Crassostrea gigas from the French Atlantic coast

Two cases of haplosporidian infection occurred during 1993 in Pacific oysters Crassostrea gigas from the French Atlantic coast. The localization and ultrastructure of the plasmodia are described. In situ hybridization of infected tissue sections was conducted with DNA probes for oyster-infecting haplosporidians. The Haplosporidium nelsoni-specific DNA probe MSX1347 hybridized with the C. gigas parasite, and the H. costale-specific probe SSO1318 did not hybridize. Total genomic DNA was extracted from the infected tissue sections for polymerase chain reaction (PCR) amplification of the haplosporidian. PCR amplifications with H. nelsoni-specific primers and with 'universal' actin primers did not yield the expected products of 573 and 700 bp, respectively. A series of primers was designed to amplify short regions of small subunit ribosomal DNA (SSU rDNA) from most haplosporidians. The primers encompass a highly variable region of the SSU rDNA and did not amplify oyster DNA. PCR amplification of the infected C. gigas genomic DNA with these primers yielded the expected-sized product from the primer pair targeting the shortest region (94 bp). This PCR product was sequenced and it was identical to the corresponding SSU rDNA region of H. nelsoni.

A quantitative competitive polymerase chain reaction assay for the oyster pathogen Perkinsus marinus

A quantitative competitive polymerase chain reaction (QCPCR) assay was developed for the oyster parasite Perkinsus marinus. PCR primers for the rRNA gene region of P. marinus amplified DNA isolated from P. marinus but not from Perkinsus atlanticus, Crassostrea virginica, or the dinoflagellates Peridinium sp., Gymnodinium sp., or Amphidinium sp. A mutagenic primer was used to create a competitor plasmid molecule identical to the P. marinus target DNA sequence except for a 13-bp deletion. Both P. marinus and competitor DNA amplified with equivalent efficiencies. Each of 25 oysters was processed by 5 P. marinus diagnostic methods--Ray's fluid thioglycollate medium (FTM) tissue assay, FTM hemolymph assay, whole oyster body burden assay, QCPCR of combined gill and mantle (gill/mantle) tissue, and QCPCR of hemolymph. The QCPCR assay enabled detection of 0.01 fg of P. marinus DNA in 1.0 microg of oyster tissue. QCPCR of gill/mantle tissue or hemolymph as well as the body burden assay detected infections in 24 of 25 oysters. Ray's FTM tissue assay detected only 19 infections. The FTM hemolymph assay detected only 22 infections. Regression analysis of QCPCR results and FTM results indicated that the QCPCR assays were effective in quantitating P. marinus infections in oyster tissues.

Rhopalobdella japonica n. gen., n. sp. (Hirudinea, Piscicolidae) from Dasyatis akajei (Chondrichthyes: Dasyatididae) in the northwestern Pacific

A new genus and species of piscicolid leech in the Platybdellinae inhabits the oral cavity of Dasyatis akajei in the northwestern Pacific Ocean near Tanabe, Japan. The genus Rhopalobdella n. gen. is characterized externally by very small oral and caudal suckers and a smooth body that is widest just posterior to the clitellum. Eyespots and ocelli are lacking. The coelom is spacious with large segmental connecting sinuses between dorsal and ventral sinuses. There are 5 pairs of testisacs, an unusually extensive epididymis, and a very large bursa. Conducting tissue is absent. There are 2 pairs of esophageal diverticula and very well developed nephridia. Rhopalobdella japonica n. gen. n. sp. is characterized by a urosome that tapers strongly to the caudal sucker and by a single gonopore; the common oviduct opens into the posterior portion of the bursa. The coelomic and excretory systems resemble Aestabdella, but in other respects the genera are quite different. This is the first marine leech reported from rays in the northwestern Pacific.

Increased Virulence in an Introduced Pathogen: Haplosporidium nelsoni (MSX) in the Eastern Oyster Crassostrea virginica

The protistan parasite Haplosporidium nelsoni has caused extensive mortality in the eastern oyster Crassostrea virginica along the mid-Atlantic coast of the United States since 1957. The origin of H. nelsoni has remained unresolved. Molecular diagnostic tools were used to examine the hypothesis that a haplosporidian parasite in the Pacific oyster C. gigas is H. nelsoni. A DNA probe specific for H. nelsoni reacted positively in in situ hybridizations with haplosporidian plasmodia from C. gigas collected in Korea, Japan, and California. Primers that specifically amplify H. nelsoni DNA in the polymerase chain reaction amplified product from Californian C. gigas infected with the haplosporidian parasite. The DNA sequence of the 565-base pair amplified product was identical to the H. nelsoni sequence except for a single nucleotide transition, a similarity of 99.8%. These results are conclusive evidence that the parasite in C. gigas is H. nelsoni and strongly support previous speculation that the parasite was introduced into Californian populations of C. gigas from Japan. Results also support previous speculation that H. nelsoni was introduced from the Pacific Ocean to C. virginica on the East Coast of the United States, likely with known importations of C. gigas. These results document greatly increased virulence in a naive host-parasite association and reinforce potential dangers of intentional, but improper, introductions of exotic marine organisms for aquaculture or resource restoration.

Higher level relationships of leeches (Annelida: Clitellata: Euhirudinea) based on morphology and gene sequences

The evolutionary patterns of divergence of seven euhirudinean families were investigated by cladistic analysis of 33 euhirudinean species. Oligochaetes, Acanthobdella peledina, and branchiobdellidans were included as outgroup taxa. Cladistic analysis employed 1.8 kb of nuclear 18S ribosomal DNA and 651 bp of mitochondrial cytochrome c oxidase subunit I in addition to morphological data. The use of two molecular data sets, one nuclear gene and one mitochondrial gene, as well as morphological data combined historical information evolving under a variety of different constraints and therefore was less susceptible to the biases that could confound the use of only one type of data. Results suggest that the nuclear 18S rDNA gene yields a meaningful historical signal for determining higher level relationships. The more rapidly evolving CO-I gene was informative for recent or local areas of the evolutionary hypothesis, such as within-family relationships. Analyses combining all data from the three character sets yielded one most-parsimonious tree. Most of the higher taxa in recent leech systematics were well corroborated in the resulting topology. However, these results suggested paraphyly of the order Rhynchobdellida, which contradicts the presence of a proboscis as a synapomorphy. The medicinal leech family Hirudinidae was polyphyletic because Haemadipsidae and Haemopidae each have a hirudinid ancestor. In addition, all but one of the genera within the family Erpobdellidae must be either abandoned or renamed. Unusual findings included compelling evidence of historical plasticity in bloodfeeding behavior, having been lost at least four times in the course of euhirudinean evolution. Biogeographic patterns supported a New World origin for Arhynchobdellida.

Perkinsus marinus tissue distribution and seasonal variation in oysters Crassostrea virginica from Florida, Virginia and New York

Perkinsus marinus infection intensity was measured in eastern oysters Crassostrea virginica collected in October and December 1993, and March, May, and July 1994 from 3 U.S. sites: Apalachicola Bay (FL), Chesapeake Bay (VA), and Oyster Bay (NY). Gill, mantle, digestive gland, adductor muscle, hemolymph, and remaining tissue (including gonadal material and rectum) were dissected from 20 oysters from each site at each collection time. Samples were separately diagnosed for P. marinus infections by incubation in Ray's Fluid Thioglycollate Medium (RFTM) and subsequent microscopic quantification of purified enlarged hypnospores. At all sampling times and sites, average P. marinus infection intensity (g wet wt tissue-1 or ml hemolymph-1) was lowest in hemolymph samples, and generally highest in the digestive gland. Perkinsus marinus prevalence was 100% at both FL and NY sites for each of the 5 collection times, and, for the VA site, was less than 100% in only 1 month (May 1994). Seasonal intensity patterns and mean total body burdens differed among the sites. Average body burden was highest in VA during October and progressively declined to a minimum in May. This decline was probably due to mortality of heavily infected oysters and diminution of parasite activity associated with colder temperatures and reduced salinities. Intensities varied little during the months of October and December at both the FL and NY sites. Minimum average intensities were observed in March in FL oysters and May in NY oysters. Relatively high P. marinus infection levels that persisted throughout the winter in NY oysters compared with VA oysters could reflect constant high salinity in Long Island Sound which favors parasite activity, and also rapid decline in temperature in the fall that may have prevented epizootic oyster mortalities.

Prevalence and distribution of QPX, Quahog Parasite Unknown, in hard clams Mercenaria mercenaria in Virginia, USA

In July 1996, the Virginia Institute of Marine Science initiated a sampling program to examine wild and cultured hard clams Mercenaria mercenaria for QPX, Quahog Parasite Unknown, a protistan parasite associated with severe mortalities of hard clams in localized areas in maritime Canada and Massachusetts, USA. The sampling program set out to seasonally monitor wild clams from one site, James River, Virginia, and cultured clams from 2 sites, Chincoteague Bay and Mattawoman Creek, Virginia. Histological examination of initial samples revealed 8% prevalence of the parasite in 1-2 yr old cultured clams in Chincoteague Bay. This is the first documentation of QPX in Virginia. To ascertain the distribution of the parasite in Virginia, the survey was expanded between August 1996 and July 1997 to include 16 additional sites. A total of 1305 wild and cultured clams was sampled from Chesapeake Bay tributaries and coastal areas where harvest and culture occur. QPX was not found in Chesapeake Bay, but was present in cultured clams from 3 coastal embayments--the original Chincoteague Bay site, Burton Bay and Quinby Inlet. The parasite was found in Chincoteague Bay at each sample period at prevalences ranging from 8 to 48%. Infections were generally light to moderate intensity and were most often observed in mantle and gill tissues. The maximum prevalence was observed in May 1997 and coincided with notable clam mortalities. QPX prevalences at the other sites were low, ranging from 4 to 15%. To date QPX has not had a significant impact on Virginia's hard clam fishery and aquaculture industry; however, the presence of the pathogen in 3 of the state's most productive hard clam growout areas warrants continued monitoring and research.

Phylogeny of leeches (Hirudinea) based on mitochondrial cytochrome c oxidase subunit I

The phylogenetic relationships of leeches were investigated for the first time using molecular data. Twenty-one species were examined representing 7 of the 10 conventionally recognized euhirudinean families. In addition, Acanthobdella peledina, a branchiobdellid, four oligochaetes, and two polychaetes were included. Cladistic analysis of the mitochondrial cytochrome c oxidase subunit I gene yielded one most-parsimonious tree. Contemporary taxonomic groupings of leeches into higher categories were found to be largely consistent with monophyletic groups identified in the analysis. Unusual relationships for which there is some precedent include a sister-group relationship between the piscicolids and Arhynchobdellida, as well as the grouping of the haemopids within Hirudinidae.

'Total evidence' refutes the inclusion of Perkinsus species in the phylum Apicomplexa

The phylogenetic affinities of the oyster pathogen Perkinsus marinus were investigated with morphology, 18S-like rDNA data and actin sequence data. Morphological investigations revealed that Perkinsus species do not have a conoid and that other criteria which have been used to place them in the Apicomplexa are general to alveolates. When considered separately, 18S-like rDNA and actin data sets each support a closer affinity for Perkinsus marinus with the dinoflagellates. However, each of these separate analyses possess their own biases and weaknesses. Use of the phylogenetic principle of 'total evidence' in which data sets are combined in simultaneous analysis yielded a more robust hypothesis that is stable both to character and taxonomic sampling. The resulting cladogram strongly corroborates the placement of Perkinsus species with the Dinoflagellida and not with the Apicomplexa.

Phylogenetic analysis of Perkinsus based on actin gene sequences

Perkinsus species presently are classified within the phylum Apicomplexa. This placement, however, is controversial. Based upon morphological observations and phylogenetic analyses of the small subunit ribosomal RNA gene, it has been suggested that Perkinsus may be more closely related to dinoflagellates. To reevaluate the phylogenetic position of Perkinsus, we obtained nucleotide sequence data for actin genes from Perkinsus marinus and 2 dinoflagellates, Prorocentrum minimum and Amphidinium carterae. Results indicated that there are 2 closely related actin genes in the genome of P. marinus. Phylogenetic comparisons of these actin gene fragments of P. marinus to available actin gene sequences for several ciliates and apicomplexans and to the 2 actin gene sequences from dinoflagellates obtained in this study supported a closer affinity of P. marinus to dinoflagellates than to apicomplexans.

Effect of in vitro exposure to tributyltin on generation of oxygen metabolites by oyster hemocytes

Mollusks depend chiefly on hemocyte-mediated cytotoxic mechanisms such as reactive oxygen species (ROS) to defend against pathogenic microorganisms. The effect of in vitro tributyltin chloride (TBT) exposure on ROS generation by oyster (Crassostrea virginica) blood phagocytes is quantified in this study. Luminol-augmented chemiluminescence (LCL) was used to measure ROS activity of resting and zymosan-stimulated cells after 1 or 20 hr TBT exposure. LCL is thought to measure primarily the activity of the myeloperoxidase/hydrogen peroxide/ halide antimicrobial pathway. Hemocytes in TBT-free medium (controls) produced low level LCL, which was markedly stimulated by the addition of zymosan particles. Both resting and zymosan-stimulated LCL values were significantly inhibited by > or = 80 ppb TBT after either 1 or 20 hr of exposure. Exposure to < or = 2 ppb TBT concentrations for 20 hr produced slightly enhanced LCL activity, suggesting a hormesis-like effect. Partial reversibility of TBT suppression of LCL took place when previously exposed cells were put in TBT-free medium. The TBT concentrations used in these studies were not cytolethal in vitro and were considerably less than oyster tissue levels recorded after chronic, sublethal in vitro exposures. The data suggest that the common aquatic contaminant TBT can interact rapidly with C. virginica hemocytes to produce a partially reversible immunotoxicological lesion. Xenobiotic-induced suppression of ROS production by hemocytes may increase host susceptibility to infectious diseases.

Phylogeny of the Haplosporidia (Eukaryota: Alveolata) based on small subunit ribosomal RNA gene sequence

The phylogenetic position of the phylum Haplosporidia was investigated with the complete small subunit rRNA gene sequences from 5 species in the phylum: Haplosporidium nelsoni and Haplosporidium costale, parasites of the eastern oyster Crassostrea virginica; Haplosporidium louisiana, a parasite of the mudcrab Panopeus herbstii; Minchinia teredinis, a parasite of shipworms (Teredo spp.) and Urosporidium crescens, a hyperparasite found in metacercariae of the trematode Megalophallus sp. in the blue crab, Callinectes sapidus. Multiple alignments of small subunit rRNA gene sequences included the 5 haplosporidian taxa and 14 taxa in the alveolate phyla Ciliophora, Dinoflagellida, and Apicomplexa. Maximum parsimony analysis placed the phylum Haplosporidia as a monophyletic group within the alveolate clade, as a taxon of equal rank with the other 3 alveolate phyla, and as a sister taxon to the clade composed of the phyla Dinoflagellida and Apicomplexa. Transversionally weighted parsimony placed the haplosporidians as a sister taxon to the ciliates. A separate analysis focused on the relationships of species in the genus Haplosporidium. Analyses were conducted with the haplosporidians as a functional ingroup, using each of the alveolate phyla individually as functional outgroups. The results indicated that species in the genus Haplosporidium do not form a monophyletic assemblage. As such, the present morphological criteria for distinguishing the genera Haplosporidium and Minchinia are insufficient.

A sensitive and specific DNA probe for the oyster pathogen Haplosporidium nelsoni

Haplosporidium nelsoni is a pathogen of the eastern oyster, Crassostrea virginica, along the middle Atlantic coast of the U.S. Genomic DNA was extracted from H. nelsoni plasmodia and small subunit (SSU) rDNA was amplified by PCR, cloned and sequenced. The sequence of H. nelsoni SSU rDNA was aligned with that of another haplosporidian, Minchinia teredinis, and with SSU rDNA data of C. virginica and various protists in GenBank. A 21-base oligonucleotide unique to H. nelsoni, designated MSX1347, was commercially synthesized and tested for sensitivity and specificity. In dot blot hybridizations the probe detected 100 pg of cloned H. nelsoni rDNA and the presence of H. nelsoni in 1 microgram of genomic DNA from an infected oyster. It did not hybridize with 1 microgram of genomic DNA from uninfected C. virginica or with cloned SSU rDNA of M. teredinis. The probe was further tested for specificity with in situ hybridizations on AFA-fixed, paraffin-embedded tissue sections. The probe hybridized well with H. nelsoni plasmodia and immature spores, but poorly with mature spores. The probe did not hybridize with oyster tissue, with other common oyster parasites such as P. marinus or Nematopsis sp., or with the haplosporidians Haplosporidium louisiana from mud crabs (Panopeus spp.), Haplosporidium costale from C. virginica or M. teredinis from shipworms (Teredo spp.).

Molecular phylogenetic evidence that the phylum Haplosporidia has an alveolate ancestry

The phylogenetic position of the phylum Haplosporidia among other protists was investigated with the complete 16S-like rRNA gene sequences from two species in the phylum: Haplosporidium nelsoni, a parasite of oysters, and Minchinia teredinis, a parasite of shipworms. Because the lack of obvious morphological homologies with other protists hampered decisions regarding taxonomic composition for sequence alignment and phylogenetic analysis, the complete sequences for these two haplosporidians were directed as search queries to the blast/ncbi.nlm.nih.gov electronic mail server. The results of this heuristic similarity search provided a basis for constructing a preliminary higher-taxonomic-level analysis comparing the haplosporidians with species from the slime molds, fungi, algae, amoebae, ciliates, dinoflagellates, and apicomplexans. Maximum parsimony yielded equivocal results, whereas transversionally weighted parsimony suggested an affinity with the alveolates (i.e., the ciliates, dinoflagellates, and apicomplexans). Multiple alignment of the two haplosporidian sequences against 17 taxa in a secondary analysis focusing on the alveolates and subsequent parsimony analysis placed the phylum Haplosporidia as a monophyletic group within the Alveolata and as a taxon of equal rank with the other three alveolate phyla. The precise placement within the Alveolata was sensitive to weighting.

Small subunit ribosomal RNA gene sequence of Minchinia teredinis (Haplosporidia: Haplosporidiidae) and a specific DNA probe and PCR primers for its detection

Minchinia teredinis is a pathogen of wood-boring molluscs (shipworms), Teredo spp., along the middle Atlantic coast of the U.S. Genomic DNA was extracted from M. teredinis spores and small subunit (SSU) rDNA was amplified by PCR, cloned, and sequenced. The sequence of M. teredinis SSU rDNA was aligned with that of Haplosporidium nelsoni and various protists in GenBank. A 22-base oligonucleotide probe unique to M. teredinis, designated MIN702, was commercially synthesized and tested for sensitivity and specificity. In dot-blot hybridizations the probe detected 500 pg of cloned M. teredinis rDNA. The probe did not hybridize with cloned SSU rDNA of Teredo spp. or H. nelsoni. The probe was further tested for specificity with in situ hybridizations on AFA-fixed, paraffin-embedded tissue sections. The probe hybridized well with M. teredinis plasmodia and immature spores, but poorly with mature spores. The probe did not hybridize with shipworm tissue or with the haplosporidians Haplosporidium louisiana from mud crabs (Panopeus spp.) or H. nelsoni and H. costale from Crassostrea virginica. The probe and a second 18-base oligonucleotide, when used as PCR primers, amplified a 536-bp fragment of the M. teredinis SSU rRNA gene. The PCR assay was able to detect 10 fg of the cloned gene and also detected the presence of M. teredinis DNA in shipworms in which infections were observed microscopically. The 536-bp amplification product was not obtained in one Teredo sp. or in one Bankia gouldi, both categorized as uninfected after microscopic inspection. The DNA probe and PCR primers appear to be specific for M. teredinis and should be useful as diagnostic tools and for life cycle investigations.

Further evidence of regular sporulation by Haplosporidium nelsoni in small oysters, Crassostrea virginica

During a field study to determine the susceptibility of the Pacific oyster Crassostrea gigas to Chesapeake Bay oyster pathogens, sporulation of Haplosporidium nelsoni was observed in eastern oysters Crassostrea virginica being used as controls. The C. virginica were obtained from 2 sources on 19 May 1993, a wild population in the upper Rappahannock River, Virginia (59.6 mm mean shell height) and a hatchery-reared population from Chesapeake Mari-culture that was held in the Wye River, Maryland (42.2 mm mean shell height); they were deployed in the York River, lower Chesapeake Bay on 29 June 1993. Both groups of C. virginica became heavily infected with H. nelsoni in early July 1993. Sporulation was observed in both groups on 8 September but was most prevalent in the smaller Maryland oysters where it reached 36% of infected oysters. Oysters of 72.3 mm mean shell height deployed at the same location in May 1993 also became heavily infected with H. nelsoni, but no cases of sporulation were observed in these larger oysters. These results provide further evidence that sporulation of H. nelsoni occurs regularly only in oysters approximately 1 yr old or less.

Acute osmotic tolerance of cultured cells of the oyster pathogen Perkinsus marinus (Apicomplexa:Perkinsida)

Cultured Perkinsus marinus cells were exposed for 24 hr to salinities of 0, 3, 6, 9, 12 and 22 ppt at temperatures of 1, 5, 10, 15 and 28 degrees C in artificial seawater (ASW) and to the same salinities at 28 degrees C in ASW with the osmotic concentration adjusted with sucrose to the equivalent of 22 ppt. At 28 degrees C mortality increased as salinity decreased below 22 ppt. Mortality was greater than 99% at 0 ppt and greater than 90% at 3 ppt. Mortality was 70% at 6 ppt, 43% at 9 ppt and 20% at 12 ppt. Mortality was low (< 5%) and equal to that at 22 ppt in all treatments where osmotic concentration was maintained with sucrose. Mortality occurred rapidly, within 5 min of exposure to experimental conditions. In the region where mortality was most sensitive to salinity changes (6-12 ppt), lower temperature caused an increase in mortality, but the temperature effect was significant only at 9 ppt.

First North American record of the marine leech Notostomum laeve (Annelida: Hirudinea)

The Arctic marine leech Notostomum laeve is reported for the first time from North America. A single, small specimen was collected in April 1990 on the external surface of 1 of 30 Greenland halibut Reinhardtius hippoglossoides from Cumberland Sound, Baffin Island, Northwest Territories, Canada. Total length of the specimen including suckers is 41 mm; maximum body width is 1.8 mm. The species is easily identified by the unusual suckers. The caudal sucker is divided into 2 lateral halves that appear to close somewhat like a clam shell; the oral sucker is very thick and muscular with a row of small, hard teeth-like papillae around the outer margin. On the basis of this report from northern Canada, N. laeve probably has a circumpolar distribution in the Arctic Ocean.

The development of a hemogregarine of Lycodes raridens from Alaska in its definitive leech host

Piscicolid leeches from the Bering Sea that had been removed from Lycodes raridens in 1977 were examined histologically. Developmental stages of a haemogregarine blood parasite of fish were found in the intestinal ceca and in salivary tissues. The developmental sequence, including gametogenesis and sporogony followed by intestinal merogonic development and anteriad migration, was the same as is known for Haemogregarina (sensu lato) myoxocephali of Atlantic sculpins. Merozoites with perinuclear crystalloid inclusions were found in the dorsal blood vessel, interstitially between the blood vessel and salivary cells and within both the somata and ductules of salivary cells. This confirms the importance of rhynchobdellid leech circulatory anatomy in facilitating the transmission of apicomplexan parasites. The lack of distinguishing characteristics precludes assigning a specific name to this parasite and may be indicative of frustrations that will be encountered in future revisions of the systematics of the genus Haemogregarina.

Increased Reactive Oxygen Intermediate Production by Hemocytes Withdrawn from Crassostrea virginica Infected with Perkinsus marinus

Perkinsus marinus is a protozoan parasite responsible for a major infectious disease of the Eastern oyster, Crassostrea virginica. Nonspecific immunity was assayed in oysters with known intensities of infection so that the physiological responses of the host elicited by the parasite could be better understood. This report describes the capacity of hemocytes to generate reactive oxygen intermediates during the progression of the disease. The hemocytes constitute the major internal defense effector system of oysters, and cytotoxic oxygen species are thought to play central roles in antimicrobial activities of hemocytes and other phagocytic cells. Production of oxyradicals by both resting and phagocytically stimulated hemocytes was quantified by luminol-augmented chemiluminescence. Hemocytes from oysters with heavy Perkinsus infections produced significantly higher levels of chemiluminescence than their counterparts withdrawn from lightly or moderately infected individuals. Furthermore, in addition to a higher chemiluminescent activity per cell, the total circulating hemocyte count was elevated in the heavily infected animals. Therefore, advanced cases of this disease seem to be characterized by hemocyte activation and recruitment, with concomitant exuberant production of hemocyte-derived reactive oxygen intermediates. The resultant oxidant load may participate in the pathogenesis of the disease.

Richardsonobdella-Lineatae, Gen Et Sp-Nov (Hirudinea), a Parasite of Meiacanthus-Lineatus (Pisces, Blenniidae) From Heron Island, Great-Barrier-Reef

Richardsonobdella, gen, nov., is characterised externally by well developed suckers, one pair of eyes, 12-annulate mid-body segments and smooth skin. Internal characters include five pairs of testisacs, small atrial-bursa complex, vector tissue with paired strands that fuse with ovisacs, fused posterior crop caeca with fenestrae, and spacious coelomic system with segmental connections among dorsal, ventral and lateral sinuses, and among testicular, dorsal and lateral sinuses, but lacking pulsatile vesicles. Richardsonobdella lineatae, sp. nov., is characterised by 21 black transverse pigment bands separated by narrow unpigmented regions. Suckers are also black; oral with two transverse unpigmented bands, caudal with 13 unpigmented radial lines. Maximum length, including suckers, is 12 mm.

Hematozoa of Fishes From Heron Island, Australia, With the Description of 2 New Species of Trypanosoma

Two species of Trypanosoma, three species of Haemogregarina and one species of Haemohormidium were found in 69 fishes belonging to 28 species. Trypanosoma mackerrasi, sp, nov., from Hemiscyllium ocellatum, measures 125 �m long by 18 �m wide, has no free flagellum, and has the kinetoplast located 37% of the body length from the posterior end. Trypanosoma taeniurae, sp. nov., from Taeniura lymma measures 55 �m long by 4 �m wide and has a free flagellum 9 �m long. Haemogregarina hemiscyllii was found in H. ocellatum, H. tetraodontis parasitised Diodon hystrix, and H. bigemina was found in Ecsenius bicolor. A species of Haemohorrnidium was found in Pomacentrus melanochir, but it could not be identified with certainty.

The seasonal antibody response in juvenile summer flounder (Paralichthys dentatus) to the hemoflagellate Trypanoplasma bullocki

An immuno-blot assay was used to investigate the serum antibody response in flounder injected with formalin-killed flagellates (immunized) and those injected with saline (control) and challenged with live T. bullocki after 21 days. Fish were held at 20 degrees C and at ambient temperature from October through June. At 20 degrees C immunized fish had significantly higher antibody titers than control fish, but immunized fish were not protected from infection with T. bullocki. At ambient temperature, after initial flagellate growth phase, antibody titer varied directly with temperature (2-25 degrees C) and T. bullocki intensity varied inversely with titer. Flagellates were eliminated from the peripheral circulation in both immunized and control fish when antibody titer peaked in May. Recovered fish were immune to homologous challenge for at least one year.

Influence of temperature on the immune response of juvenile summer flounder, Paralichthys dentatus, and its role in the elimination of Trypanoplasma bullocki infections

Two groups of juvenile summer flounder maintained at 5 degrees C were experimentally infected with the hemoflagellate Trypanoplasma bullocki. Another group maintained at 5 degrees C was not infected. The water temperature of one infected group was raised stepwise to 12 degrees C, 18 degrees C, and 24 degrees C for 2 to 3 weeks at each level. The other infected group was maintained at 5 degrees C for 12 weeks, the duration of the experiment. In addition, juvenile flounder were collected over a temperature range of 6 degrees C to 22 degrees C from February to June, 1982, to monitor natural infections. Live T. bullocki were incubated in plasma from fish at each temperature to monitor the host's humoral response. Trypanoplasmacidal lysis occurred in experimental infections maintained at 24 degrees C and in natural infections over a range experimental infections at 24 degrees C and in natural infections at 22 degrees C. Differences in temperature where lytic activity occurred was mainly attributable to the short time exposure of experimental infections to increasing temperatures in contrast to that occurring in nature. Trypanoplasmacidal lysis with increasing water temperatures in flounder indicates that the fish's humoral immunity is responsible for the annual spring decline in prevalence and eventual elimination of T. bullocki infections.