Phylogenetic analyses of 18S rDNA gene data for Choreonema thuretii (Corallinales, Rhodophyta) and available data for other coralline red algae indicated that Choreonema belongs to the same lineage as other taxa of Corallinales possessing tetra/bisporangial conceptacles with multiporate plates. These results, when integrated with extant morphological/anatomical data, ultrastructural data, and taxonomic data led to the conclusion that all taxa of Corallinales possessing multiporate conceptacles belong to a distinct family, the Hapalidiaceae. Recognition of the Hapalidiaceae as a distinct family was supported both phylogenetically and phenetically. The Hapalidiaceae includes those taxa of Corallinales whose tetrasporangia produce zonately arranged spores and whose tetra/bisporangia are borne in conceptacles, produce apical plugs, and develop beneath multiporate plates. The Hapalidiaceae includes the subfamilies Choreonematoideae, Melobesioideae, and Austrolithoideae, formerly placed in the Corallinaceae sensu lato. The Choreonematoideae lack cell connections between adjacent vegetative filaments and have a multiporate plate that is acellular at maturity, consisting only of a calcium carbonate matrix. The Austrolithoideae and Melobesioideae both have cellular pore plates; taxa of Melobesioideae have cell fusions between cells of adjacent vegetative filaments, whereas taxa of Austrolithoideae lack cellular connections between adjacent vegetative filaments. Inclusion of the Austrolithoideae in the Hapalidiaceae was based entirely on morphological/anatomical evidence; molecular evidence currently is lacking. Relevant historical and nomenclatural data are included.

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Coralline algae (Corallinales, Rhodophyta) that form rhodoliths are important ecosystem engineers and carbonate producers in many polar coastal habitats. This study deals with rhodolith communities from Floskjeret (78A degrees 18'N), Krossfjorden (79A degrees 08'N), and Mosselbukta (79A degrees 53'N), off Spitsbergen Island, Svalbard Archipelago, Norway. Strong seasonal variations in temperature, salinity, light regime, sea-ice coverage, and turbidity characterize these localities. The coralline algal flora consists of Lithothamnion glaciale and Phymatolithon tenue. Well-developed rhodoliths were recorded between 27 and 47 m water depth, while coralline algal encrustations on lithoclastic cobbles were detected down to 77 m water depth. At all sites, ambient waters were saturated with respect to both aragonite and calcite, and the rhodolith beds were located predominately at dysphotic water depths. The rhodolith-associated macrobenthic fauna included grazing organisms such as chitons and echinoids. With decreasing water depth, the rhodolith pavements were regularly overgrown by non-calcareous Polysiphonia-like red algae. The corallines are thriving and are highly specialized in their adaptations to the physical environment as well as in their interaction with the associated benthic fauna, which is similar to other polar rhodolith communities. The marine environment of Spitsbergen is already affected by a climate-driven ecological regime shift and will lead to an increased borealization in the near future, with presently unpredictable consequences for coralline red algal communities

This paper provides the first monographic account of south-eastern Australian representatives of the Hapalidiaceae (Corallinales, Rhodophyta). The Hapalidiaceae includes those Corallinales whose tetrasporangia produce zonately arranged spores, and whose tetrasporangia/bisporangia are borne in conceptacles, produce apical plugs, develop beneath multiporate plates or roofs, and are not enclosed individually within calcified sporangial compartments. The Hapalidiaceae contains the subfamilies Choreonematoideae, Melobesioideae and Austrolithoideae, all formerly placed in the Corallinaceae sensu lato. The Choreonematoideae is represented in south-eastern Australia by a single species, Choreonema thuretii. The Melobesioideae is represented by five genera (Melobesia, Lithothamnion, Phymatolithon, Mesophyllum, Synarthrophyton) and eight species. Synarthrophyton pseudosorus sp. nov. is newly described. The presence of tetrasporangial conceptacles occurring in irregularly shaped dense clusters that contain both discrete conceptacles and fused groups of conceptacles delimits this species from all other species of Synarthrophyton. Morphological and anatomical accounts are provided, including keys, information on distribution, habitat and nomenclature. Brief biogeographic comparisons between south-eastern Australia and neighbouring regions are also made.

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