Sequence data of the rbcL–rbcS noncoding intergenic spacer of the plastid genome for 47 specimens of Porphyra and Bangia from the northeast Atlantic reveal that they fall into 11 distinct sequences: P. purpurea, P. dioica (includes a sample of P. “ochotensis” from Helgoland), P. amplissima (includes P. thulaea and British records of P. “miniata”), P. linearis, P. umbilicalis, P. “miniata”, B. atropurpurea s.l. from Denmark and B. atropurpurea s.l. from Wales, P. drachii, P. leucosticta (includes a British record of P. “miniata var. abyssicola”), and P. “insolita” (includes P. “yezoensis” from Helgoland). Of these, data obtained for P. purpurea, P. dioica, P. amplissima, P. linearis, P. umbilicalis, P. drachii, and P. leucosticta were based on type specimens or material compared with types. Comparison of sequence data for Porphyra spp. and Bangia atropurpurea s.l. (including B. fuscopurpurea, the type species of Bangia) confirms that the species are congeneric. The data also confirm that the number of layers that make up the Porphyra thallus are not taxonomically significant. Comparison of sequence data for species from the northeast Atlantic with those for material of two species from the Pacific reveals that the species fall into two distinct groupings: an Atlantic group, containing P. purpurea, P. dioica, P. amplissima, P. linearis, P. umbilicalis, P. “miniata”, and B. atropurpurea, and a Pacific group, containing P. “pseudolinearis”, P. drachii, P. leucosticta, P. “yezoensis” (including a sample of P. “tenera”), and P. “insolita” (including P. “yezoensis” from Helgoland). The possibility of alien species in the northeast Atlantic is discussed.

The Corallinoideae (Corallinaceae) is represented in the northeastern Atlantic by Corallina officinalis L.; Corallina elongata J. Ellis et Sol.; Haliptilon squamatum (L.) H. W. Johans., L. M. Irvine et A. M. Webster; and Jania rubens (L.) J. V. Lamour. The delimitation of these geniculate coralline red algae is based primarily on morphological characters. Molecular analysis based on cox1 and 18S rRNA gene phylogenies supported the division of the Corallinoideae into the tribes Janieae and Corallineae. Within the Janieae, a sequence difference of 46-48 bp (8.6%-8.9%) between specimens of H. squamatum and J. rubens in the cox1 phylogeny leads us to conclude that they are congeneric. J. rubens var. rubens and J. rubens var. corniculata (L.) Yendo clustered together in both phylogenies, suggesting that for those genes, there was no genetic basis for the morphological variation. Within the Corallineae, it appears that in some regions, the name C. elongata has been misapplied. C. officinalis samples formed two clusters that differed by 45-54 bp (8.4%-10.0%), indicating species-level divergence, and morphological differences were sufficient to define two species. One of these clusters was consistent with the morphology of the type specimen of C. officinalis (LINN 1293.9). The other species cluster is therefore described here as Corallina caespitosa sp. nov. This study has demonstrated that there is a clear need for a revision of the genus Corallina to determine the extent of ''pseudocryptic'' diversity in this group of red algae.

Lithothamnion tophiforme (Esper) Unger is a dominant, arctic, saxicolous species that extends southward, albeit with reduced cover, into the deeper colder waters of the North Atlantic subarctic, where it also occurs in significant rhodolith deposits with L. glaciale. The external appearance of L. tophiforme is distinctive, but typification, anatomy, reproduction, ecology, and biogeography have not been previously analyzed. These topics are now addressed, with extensive use of SEM, in comparison with other North Atlantic arctic and subarctic melobesioid genera and species. The species considered in this article comprise 95% of the coralline biomass of the colder North Atlantic and adjacent arctic (i.e. less than 121 C summer and less than 01 C winter). In the outer thallus region of coralline algae, crust extension proceeds, calcification develops, surface sloughing and grazing occur, and reproductive structures are initiated. Analysis of the ultrastructure of the outer thallus region (epithallium, meristem, and perithallium) of L. tophiforme shows distinctive generic similarities and specific differences from the other Lithothamnion species discussed here. Considerable generic differences from the Clathromorpum and Leptophytum species also encountered in the region considered are highlighted as well. We discuss the functional and taxonomic implications of these distinguishing features and recommend that they be more widely considered in future research on coralline algae to understand more fully the ecology and evolution of the Corallinales. Adey 1973) quantitatively collected crustose corallines from west to east across a broad northern North Atlantic band. The biology and ecology of many species in these collections were analyzed and the results published in the studies cited above. Irvine and Chamberlain (1994) later expanded knowledge of the species that also occur in the British Isles, and Adey and Steneck (2001) used the field data of the 1960s and 1970s as a first validation for their theoretical biogeographic model. These data showed a strong correlation between the physical/time-based predicted biogeographic regions of the model with the areal distribution of coralline species. Of the three arctic species occurring in those collections (Lithothamnion tophiforme, Leptophytum foecundum, and Kvaleya epilaeve; Adey and Steneck 2001), L. tophiforme was the least known because it had not been the subject of any anatomical/reproductive analyses. In this article we assess the taxonomy of L. tophiforme and consider its history, nomenclature, and typification. Based on light and scanning electron microscope preparations, we describe its morphology, anatomy, reproduction, and ecology. SEM was also used to reexamine the corallinaceous species ecologically associated with L. tophiforme. The use of SEM, which has increased in coralline analysis in the last decade, has tended to be restricted to low magnification (o1000Â) gross anatomy (Irvine and Chamberlain 1994, Cabioch andMendoza 2003). We have applied SEM at high...

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