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A new species of Rhytidocystis (Apicomplexa) is characterized from North American waters of the Atlantic Ocean using electron microscopy and phylogenetic analyses of small subunit (SSU) rDNA sequences. Rhytidocystis polygordiae n. sp. is a parasite of the polychaete Polygordius sp. and becomes the fourth described species within this genus. The trophozoites of R. polygordiae were relatively small oblong cells (L=35-55 microm; W=20-25 microm) and distinctive in possessing subterminal indentations at both ends of the cell. The surface of the trophozoites had six to eight longitudinal series of small transverse folds and several micropores arranged in short linear rows. The trophozoites of R. polygordiae were positioned beneath the brush border of the intestinal epithelium but appeared to reside between the epithelial cells within the extracellular matrix rather than within the cells. The trophozoites possessed a uniform distribution of paraglycogen granules, putative apicoplasts, mitochondria with tubular cristae, and a centrally positioned nucleus. The trophozoites were non-motile and lacked a mucron and an apical complex. Intracellular sporozoites of R. polygordiae had a conoid, a few rhoptries, micronemes, dense granules, and a posteriorly positioned nucleus. Phylogenies inferred from SSU rDNA sequences demonstrated a close relationship between R. polygordiae and the poorly known parasite reported from the hemolymph of the giant clam Tridacna crocea. The rhytidocystid clade diverged early in the apicomplexan radiation and showed a weak affinity to a clade consisting of cryptosporidian parasites, monocystids, and neogregarines.

This is the first comprehensive study of the community structure and spatial distribution of macrofauna in deep, muddy sediments of Placentia Bay, Newfoundland, and the adjacent shelf. The study examines the influence of water column (e.g. chlorophyll a [chl a], temperature and salinity) and sediment characteristics (e.g. grain size, carbon and nitrogen content) on infaunal patterns. Box-core samples were collected at 10 sites in June and July of 1998 from the head of the bay to the edge of the continental shelf. Multivariate analyses of community composition and environmental variation indicated inshore and offshore groupings. Inshore communities had lower species richness, diversity and densities. Fauna living deeper in the sediment were also more abundant in offshore areas. The inshore region was characterised by greater mixed-layer temperatures, higher surface chl a and large amounts of relatively fresh organic carbon (low C/N ratios) in sediments. Within the inshore sites, high levels of organic carbon influenced macrofaunal assemblages that were similar to those characteristic of organic-rich areas. Surface chl a concentration was positively correlated with sedimentary organic carbon, which was the most important predictor of infaunal abundance. At broad scales, surface chl a and sedimentary organic carbon were negatively related to infaunal abundance. Moreover, this pattern was confounded by particularly low densities at 3 inshore sites where organic levels were very high, and elevated densities at 1 productive offshore site. Low densities at these 3 inshore sites may be a result of sulphide production in sediments, or of poor food quality. Broad-scale patterns (inshore vs offshore) of community composition and abundance in Placentia Bay are largely influenced by surface oceanography through production export.

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A new species of Polygordiidae, Polygordius jouinae sp. nov., along with its distribution, habitat, and reproduction is described. Polygordius jouinae sp. nov., the first North American Polygordius, is a dominant member of macrofaunal communities on the inner continental shelf, and in bays and harbours from Massachusetts to southern New Jersey. It is distinguished from most other Polygordius species by its non-inflated, heavily ciliated pygidium, absence of pygidial glands, and a conical (rather than rounded) prostomium. The 18S SSU rDNA from P. jouinae sp. nov. was sequenced and represents the first named Polygordius species with a DNA reference in GenBank. Spearman rank correlation of sediment grain size with density of P. jouinae sp. nov. at a New Jersey site showed that density was significantly (P<0.05; N=92) positively correlated with the proportion of medium to very coarse sand and negatively correlated with the fine sand fractions. Ecologically, P. jouinae sp. nov. is an important macrofaunal species given its widespread distribution and its fidelity for coarse sand habitats. Thus, its relative abundance may be useful as an indicator of changing sedimentary conditions.