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Phymatolithon  Foslie is one of the most studied and ecologically important genera of crustose coralline algae (CCA) due to their dominant abundance in various marine ecosystems worldwide. The taxonomy of the genus is complex and has been revised and updated many times based on morphological and molecular analyses. We report on a crustose coralline algal species collected in June 2011 via snorkeling in the subtidal zone along the beach Abu Qir on the Mediterranean coast of Egypt, as part of a larger macroalgal diversity survey in the region. The species shows significant sequence divergences (3.5%–14.8% in rbc L; 2.9%–11% in psb A) from other closely related Phymatolithon taxa. Morpho-anatomically, this species possesses the characters considered collectively diagnostic of the genus Phymatolithon , namely, thalli non-geniculate epithelial cells and non-photosynthetic and domed-shaped meristematic cells, usually as short with progressive elongation of their perithallial derivatives. Based on molecular and morphological analyses, we determined that these specimens encompass a new, distinct species that we herein name Phymatolithon abuqirensis. Including this new species, the total number of described Phymatolithon species found in the Mediterranean Sea is now six. 

The recently described crustose calcifying red algal species Ramicrusta hawaiiensis, known only from mesophotic depths off Lehua Island, west of Kaua’i Island, was found in shallow benthic reef habitats (3-18 m deep) along the western coast of Hawai’i Island. Molecular and microscopy techniques were used for genetic confirmation and for detailed morphological and anatomical examination. Two independent benthic cover survey datasets collected from west Hawai’i Island were used to investigate temporal and geographic distribution of Ramicrusta . In both datasets, we report Ramicrusta at approximately 60% of the sites surveyed. Benthic cover for this alga varies among sites and among years and its presence in west Hawai’i is evident since at least 2003. These findings help to document Hawaiian coral reef ecosystem change and benthic community composition reshuffling. This study also emphasizes the critical importance of taxonomy and proper identification of macroalgal species to understand the potential for phase-shifts of dominant taxa in coral reef ecosystems after environmental disturbances and fluctuations in abiotic factors. In the last decade, members of the red algal order Peyssonneliales have increased in abundance and overgrown other benthic species in reef ecosystems in the Caribbean and tropical Pacific. The novel aspect of finding abundant Ramicrusta in much shallower water than originally described, the decadal presence of Ramicrusta , and its potential for competition with other benthic organisms make this research valuable to coral reef ecology and justify further investigation of Ramicrusta ecology and biology in the Hawaiian Islands and globally. 

In the past, non-geniculate coralline algae in the northwestern Gulf of Mexico have been identified based primarily on comparative morpho-anatomy. Recent studies employing DNA sequencing techniques combined with morpho-anatomical studies using SEM have revealed a wealth of previously undocumented diversity of rhodolith-forming non-geniculate coralline algae in the Corallinales, Hapalidiales and Sporolithales from mesophotic hard bank communities at 45-90 meters depth. Although many advances in the last decade have been made in clarifying species names and describing new species of corallines from offshore Louisiana and Texas, total diversity estimates are still incomplete and many species remain to be described. Collections from offshore Louisiana at Parker Bank in the newly expanded Flower Garden Banks National Marine Sanctuary yielded thin, finely branched rhodoliths. DNA sequence analyses of plastid-encoded psb A and rbc L loci, and nuclear-encoded LSU rDNA of these rhodolith-forming specimens revealed that some belong to an unnamed species of Sporolithon (Sporolithales) that we herein newly describe. Additionally, comparative DNA sequence analyses of rhodolith collections from Ewing Bank and other hard banks offshore Louisiana were conducted to assess rhodolith diversity in these mesophotic communities. The results revealed new reports of taxa for the region, including new rhodolith-forming species of Roseolithon (Hapalidiales) to be described herein as well. Our new biodiversity findings will be compared with historical studies from the NW Gulf of Mexico. 

Twenty-one samples belonging to species of Spyridia Harvey with uncinate (= hookshaped) spines on determinate lateral branches were investigated for their morphology with a focus on the structure of determinate branches, and for comparative chloroplast-encoded rbcL and nuclear LSU rDNA sequence analysis to elucidate their taxonomy and phylogeny. Currently, four Spyridia species with uncinate spines are recognized worldwide: S. alternans, S. cupressina, S. horridula and S. hypnoides. Of them, S. hypnoides has been recognized as the most common species with uncinate spines. In this study, we show that S. aculeata needs to be resurrected from S. hypnoides, and recognized as a distinct species based on samples from Israel, Red Sea, near the type locality. Spyridia aculeata is characterized by the spiral arrangement of determinate branches, incompletely corticated determinate branches, naked basal segment of determinate branches, by the presence of only acropetal cortication in the nodes of determinate branches, and by uncinate spines at the terminal node and on the first and second nodes of determinate branches. In our molecular analyses based on rbcL and LSU rDNA, although four Spyridia species with uncinate spines are supported on phylogenetic trees, they are not a monophyletic group. The feature of uncinate spines in Spyridia is recognized as a polyphyletic character. Our phylogenetic analysis using rbcL and LSU rDNA sequences reveals high gene sequence divergence (6.8–7.0% for rbcL and 1.2–1.3% for LSU rDNA) between samples of S. aculeata and S. hypnoides. Therefore, the distribution of S. hypnoides may be restricted to the Indian Ocean, whereas S. aculeata is widely distributed in the Atlantic Ocean including the Mediterranean Sea and the Red Sea. Another Spyridia species with uncinate spines, S. alternans, is recognized as a synonym of S. horridula by our detailed morphological observations of its type specimen. 

DNA sequence analysis of plastid-encoded psbA and rbcL loci, and nuclear-encoded LSU rDNA of rhodolith-forming specimens of Sporolithales from Brazil and the northwestern Gulf of Mexico reveal that they belong to an unnamed species of Sporolithon (Sporolithaceae). Sporolithon amadoi sp. nov. is morpho-anatomically characterized by a vegetative thallus reaching more than 20 cell layers, a tetrasporophyte with tetrasporangial sori slightly raised above the thallus surface that become overgrown and buried after spore release, and by cruciately divided tetrasporangia with pores surrounded by 9–13 rosette cells. Since these morpho-anatomical features are shared with some other Sporolithon species, identification of this species can only be confirmed by DNA sequences. 

DNA sequence analysis of plastid-encoded psbA and UPA, mitochondrion-encoded COI, and nuclear-encoded LSU rDNA of rhodolith-forming crustose coralline algal specimens from the northwestern Gulf of Mexico reveals that Mesophyllum erubescens (Foslie) Me. Lemoine is present in mesophotic rhodolith beds offshore Louisiana and Texas at 39–57 m depth. Morpho-anatomical characters viewed with SEM support the identification of these specimens. Mesophyllum erubescens is reported for the first time offshore Louisiana at Ewing Bank, the Louisiana–Texas border at Bright Bank, and Texas in the Flower Garden Banks National Marine Sanctuary.