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Main conclusionSignificantly thickened corner middle lamella of the hydroid cell wall in the stipe of dendroid moss Hypnodendron menziesii has a mechanical support function.The hydroid cell walls of the erect stipe of Hypnodendron menziesii were investigated using light microscopy (LM), transmission electron microscopy (TEM), and TEM-immunogold labeling in support of the proposed biomechanical function for the highly thickened cell corner middle lamellae. The statistical analyses of dimensions of hydroid cell and wall parameters revealed a strong positive correlation between the area of hydroid cell and (i) the hydroid cell walls adhering to thick corner middle lamella, (ii) the area of the thick cell wall at hydroid corners, and (iii) the maximum thickness of cell wall at hydroid corners. The total area of the thick cell wall at the hydroid corners concomitantly increased with the area of the hydroid cell wall adhering to the middle lamella, and with the increased number of hydroids surrounding a reference hydroid. The results suggest that markedly thickened middle lamellae of the hydroid cell wall in Hypnodendron likely function by preventing hydroid cells from collapsing under the tensile forces generated from the transpirational pull on the water column. The specific localization of (1→4)- β-D-galactan and (1,5)-α-L-arabinan in the interface region of the hydroid cell wall and the thick middle lamella is consistent with these cell wall components being involved in the mechanical strengthening of the interface through firm adhesion as well as elasticity, ensuring the structural stability of this cell wall region, which may be prone to delamination/fracturing from the various internal and external pressures imposed. The copious presence of homogalacturonan in the thick middle lamella may further enhance the strength and flexibility of hydroid cell walls.

As the demand for chitin grows, new chitin sources with unique physicochemical properties are required. Abundant biofouling species, such as amphipods and hydroids, have chitinous skeletal systems that can be utilized for chitin production. However, little is known about these chitin sources. This study investigated the viability of amphipods (Jassa sp.) and hydroids (Coryne sp.) obtained from aquaculture biofouling assemblages as novel sources of chitin. Chitin was extracted from these sources and characterized in terms of its degree of acetylation (DA), crystallinity index (CrI), molecular weight (MW), thermal stability, and surface morphology. Physiochemical characteristics where then compared against commercially available shrimp chitin. Results show that a 32.75% chitin yield can be obtained from hydroids. The percentage DA for amphipod (AC) and hydroid (HC) chitin is 58.4–59.2% and 64.8–66.7%, respectively. AC is characterized as α-chitin with a low molecular weight (MW), while HC is medium-MW β-chitin. This finding is significant because it shows hydroids to be a new source of rare β-chitin. In addition, AC has higher thermal stability than HC. AC and HC greatly differ in terms of surface morphology. Therefore, the chitin biomaterials extracted from amphipods and hydroids have different but favorable properties that can be used for diverse applications.

Interspecific associations are common in coral reefs, but those involving hydrozoans and octocorals have not been widely investigated. The hydroid Pteroclava krempfi (Hydrozoa, Cladocorynidae) lives in association with different soft coral taxa (Alcyonacea), showing a widespread distribution. However, very little information is available on the ecology of these relationships. Here, we tested for differences in the taxon-specific prevalence and habitat preference of the symbiosis and determined ecological traits of the P. krempfi–host associations in central Red Sea reefs. P. krempfi was found associated with the alcyonacean genera Lobophytum, Rhytisma, Sarcophyton and Sinularia, updating its host range and geographic distribution. The symbiosis prevalence was high in the area and especially at inshore sites compared to midshore and offshore sites. Rhytisma was the most common host, while the association with Lobophytum showed the lowest taxon-specific prevalence. P. krempfi did not show a clear preference for a specific alcyonacean size, and an increase in host size automatically led to an increase in the surface occupied by hydrozoans, although they rarely colonized more than 50% of the upper surface of the host. The spatial distribution of the hydroids on the host surface appeared related to the host genus and size as well as to the coverage of the hydroids. Despite the nature of this symbiosis requiring further investigation, P. krempfi did not seem to play a role in affecting the bleaching susceptibilities of the host colonies. The study shows that the Red Sea coral reef symbioses are more widespread than previously known and therefore deserve more attention.

Serpulid polychaetes are a unique and highly specialised group of marine segmented worms that have adapted to inhabiting self-secreted calcareous tubes attached to a wide range of hard substrates. These animals are found across all depths and habitats of the world's oceans, and some form mutually beneficial associations with live corals. The genus Hydroides is of special concern and importance, as it is not only the largest, but also one of the most ecologically and economically important groups of marine invertebrates because it includes notorious biofoulers and common bioinvaders that travel around the world hitchhiking on ships' hulls.This is the first fully illustrated guide to this notorious serpulid genus of calcareous tubeworms, providing a comprehensive diagnostic treatment of all known species of the genus Hydroides. This important reference provides reliable identification tools to distinguish Australian tubeworms from potential alien invaders that constantly arrive from overseas and threaten Australia's maritime transport, trade and mariculture.

Research on biofouling assemblages in large ports is crucial for economic, environmental and regulatory purposes, as it provides critical information for managing marine ecosystems, preventing the spread of invasive species and developing effective antifouling strategies. Hydrozoans are among the most common invertebrates found in marine biofouling communities, making them a priority taxon for monitoring and identification in large ports. In this study, we documented the diversity of benthic hydrozoans growing on three types of artificial panels (wood, plastic, and rope) submerged for three months in the major commercial ports of Ambarli, Haydarpasa, Kocaeli, and Bandirma, located in the Sea of Marmara. Seven species of hydrozoans (Ectopleura crocea, Obelia dichotoma, Bougainvillia muscus, Clytia gracilis, Eudendrium capillare, Eudendrium merulum and Sertularella ellisii) were observed throughout the study. Unique fouling hydrozoan assemblages were identified in each port, regardless of the type of panel used, suggesting that differences in the pool of species available for recruitment and port-specific conditions have a greater impact on the structure of local fouling assemblages than the type of substrate. Ectopleura crocea, a species typical of artificial substrates and characterized by high invasive potential, was recorded for the first time in the Sea of Marmara during this study.

Gorgonian corals form complex interactions with a wide range of microorganisms, which play a key role in maintaining health of the holobiont. To assess the influence that various members of the microbial community exert on the coral lipidome, we analyzed storage (triacylglycerols (TG) and monoalkyldiacylglycerols) and structural (phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol and lyso-phosphatidylcholine) lipid molecular species. A molecular-genetics analysis showed that colonies of Junceella fragilis were associated with Symbiodinium clade C. Sequences of the parasitic dinoflagellate Blastodinium contortum were found in the gorgonian Dichotella sp. Colonies of Astrogorgia rubra were associated with the filiferan hydroid Hydrichthella epigorgia. Fungal sequences were found in Dichotella sp., A. rubra and Menella sp. A molecular species of ether phospholipids with fungal hydroxylated fatty acids (FA), bacterial odd-numbered FAs and alkyl moiety were detected in gorgonian lipids. As both host coral and some bacteria can synthesize ether lipids, a conclusion was drawn that lipids are likely to be transported from members of the microbial community to the coral host, and some molecular species with an odd-numbered alkyl moiety can be derived from anaerobic bacteria. The TG content of the symbiotic gorgonian J. fragilis was 30-fold higher than in asymbiotic gorgonians. TG 18:3/18:4/18:3 can be considered as a marker of zooxanthellae presence in coral. The hydroid H. epigorgia association did not have any evident contribution to the lipid profile of gorgonian A. rubra. Such markers of soft corals as 24:6n-3 and 24:5n-6 PUFAs were found to be distributed in molecular species of lipids of all the studied corals. A high content of these acids was observed as a characteristic feature in corals of the family Plexauridae (Menella sp. and A. rubra). The lipidomic approach allows assessment of the distribution of marker fatty acids in coral lipids, and to tracing the relationships between the microbial community and the coral host.

The ubiquitous feather mosses Pleurozium schreberi and Hylocomium splendens form a thick, continuous boundary layer between the soil and the atmosphere, and play important roles in hydrology and nutrient cycling in tundra and boreal ecosystems. The water fluxes among these mosses and environmental factors controlling them are poorly understood. The aim of this study was to investigate whether feather mosses are capable of internal transport and to provide a better understanding of species-specific morphological traits underlying this function. The impacts of environmental conditions on their internal transport rates were also investigated. Cells involved in water and food conduction in P. schreberi and H. splendens were identified by transmission electron microscopy. Symplasmic and apoplasmic fluorescent tracers were applied to the moss stems to determine the routes of internal short- and long-distance transport and the impact of air humidity on the transport rates. Symplasmic transport over short distances occurs via food-conducting cells in both mosses. Pleurozium schreberi is also capable of apoplasmic internal long-distance transport via a central strand of hydroids. These are absent in H. splendens. Reduced air humidity significantly increased the internal transport of both species, and the increase was significantly faster for P. schreberi than for H. splendens. Pleurozium schreberi and Hylocomium splendens are capable of internal transport but the pathway and conductivity differ due to differences in stem anatomy. These results help explain their varying desiccation tolerance and possibly their differing physiology and autecology and, ultimately, their impact on ecosystem functioning.

Interest in the physiology of proliferation has been generated by human proliferative diseases, i.e., cancers. A vast literature exists on the Warburg effect, which is characterized by aerobic glycolysis, diminished oxygen uptake, and lactate secretion. While these features could be rationalized via the production of biosynthetic precursors, lactate secretion does not fit this paradigm, as it wastes precursors. Forming lactate from pyruvate allows for reoxidizing cytosolic NADH, which is crucial for continued glycolysis and may allow for maintaining large pools of metabolic intermediates. Alternatively, lactate production may not be adaptive, but rather reflect metabolic constraints. A broader sampling of the physiology of proliferation, particularly in organisms that could reoxidize NADH using other pathways, may be necessary to understand the Warburg effect. The best-studied metazoans (e.g., worms, flies, and mice) may not be suitable, as they undergo limited proliferation before initiating meiosis. In contrast, some metazoans (e.g., colonial marine hydrozoans) exhibit a stage in the life cycle (the polyp stage) that only undergoes mitotic proliferation and never carries out meiosis (the medusa stage performs this). Such organisms are prime candidates for general studies of proliferation in multicellular organisms and could at least complement the short-generation models of modern biology.

The Arctic and Antarctic share many oceanographical features but differ greatly in their geological histories. These divergent aspects lead to similarities and differences between the sets of species inhabiting the poles. However, the patterns are not unambiguously homogenous throughout the tree of life. For the first time, Hydrozoa (Leptothecata and Anthoathecata) is used as a model group to study patterns of diversity, distribution, bathymetry and life history strategies between the polar regions. The analyses are based on a comprehensive literature survey of hydrozoan records. Subtle differences in species richness and contrasting values of endemism are found between the Antarctic (252 species and 58% endemics) and Arctic (233 species and 20% endemics) regions. Shared trends include the lack of a medusa stage in most of the representatives, a high percentage of rarity (Arctic: 49%; Antarctic: 63%), and few common species (18% in both regions). A few species (Grammaria abietina, Obelia longissima and Paragotoea bathybia) and genera (Bouillonia and Gymnogonos) might be tentatively considered bipolar, but further molecular investigation is recommended. The bathymetric distribution mirrors the geomorphological characteristics of each region. The highest species richness occurred in the continental shelves of both polar regions. Updated inventories from each polar region are provided as supplementary material. The present work establishes a fundamental step towards an integrated bipolar framework for the study of diversity and ecology of polar regions, laying the foundation for future approaches on a wide array of topics, from origin and diversification, to changes in the distribution of polar biota.