Many marine invertebrates are intermediate hosts to parasites. As some of these parasites may influence host behaviour and act as cryptic agents involved in mass mortality, knowledge of their presence, dynamics, and life cycles is important. Our aim with the present study is to provide a survey of parasites in subtidal cockles in the Limfjorden (Denmark), to examine their influence on cockles, and to assess their possible role in the surfacing of cockles, as this phenomenon is considered a prelude to mortality. The trematode fauna of the studied subtidal population was poor in species, but about 19% of the examined cockles in late summer and autumn were infected by Monorchis parvus – a species not previously reported from cockles in Danish waters. Heavily infected cockles were filled with small, undulating, worm-like sporocysts, each filled with metacercariae. From August to November, the number of metacercariae in sporocysts increased, and at a certain point, the growing stock of sporocysts is supposed to reach a level where the cockle is unable to perform vital life functions. Our data show that infected individuals exhibit less annual shell growth than uninfected ones. There was no significant difference in the prevalence of M. parvus between unburied and buried cockles. Cockle-eating fish from the family Sparidae are known as final hosts to M. parvus, but these fish do not occur in Danish waters. Therefore, the record-high presence of M. parvus in cockles from the Limfjorden is surprising, and we consider alternative life cycle options for this trematode.

‘Tropicalization’, the phenomenon of species shifting their ranges, has become increasingly prevalent as a response to environmental modifications induced by global change. This study points to an accelerated tropicalization process of marine fish species in the Gulf of Cadiz, a bioinvasion hotspot adjacent to the Strait of Gibraltar. We report accelerated, unusual, and rare occurrences of 15 fish species expanding and potentially establishing their ranges in the Gulf of Cadiz, driven by ocean warming over the past decade. These new insights are the combined consequence of a range expansion of some species, likely facilitated by temperature increases, an intensification of maritime traffic (with a consequent rise in propagule pressure), and a possible increase in sampling efforts and citizen science.

In situ observation of cephalopods is crucial for understanding their behaviour, ecology, and natural interactions. Scientific diving offers a minimally invasive approach to studying these elusive organisms, especially in shallow waters. This systematic review evaluates the application of scientific diving in cephalopod research over the past five decades, analysing trends, methodologies, and global representation. An initial database search was conducted, followed by a second, more targeted search to improve accuracy and coverage. This two-stage process significantly increased the capture rate of relevant studies, from an estimated 28% to 57%, of 225 publications meeting inclusion criteria since 1973. In total, 83 different species were studied, with Octopus cf vulgaris being the most recurrent complex species. Most studies were conducted within recreational and non-decompression diving limits, resulting in a higher representation of orders typically found within these depth ranges: Octopoda (52.7%), Sepiida (19.8%), and Myopsida (18.7%). Orders often inhabiting greater depths, such as Nautilida (4.9%) and Oegopsida (3.8%), were studied primarily through video recordings, egg collections, or specimen release. Manual collection (44%) and direct observations (35%) were the primary goal for diving uses. Publications concentrated in regions such as the West Coast of North and South America and the Mediterranean, with the United States leading contributions (21.2%). The initial under-representation of studies was largely due to inconsistent terminology and lack of direct reference to diving methods in titles, abstracts, or keywords. These findings highlight the need for standardized reporting to fully leverage scientific diving’s potential in cephalopod research.

Despite the importance of the commercially harvested benthopelagic fish Beryx mollis, little information is available on their adult phase and reproduction. This is likely due to the low abundance of this species compared to Beryx splendens and Beryx decadactylus as well as misidentification of Beryx spp. In this study, early life stages of B. mollis were found in the southwest region off Sri Lanka during a survey with research vessel Dr Fridtjof Nansen in 2018, coinciding with the southwest monsoon period. As morphological characteristics of eggs and larval stages of the three Beryx spp. are very similar, visual identification to differentiate to species level has always been challenging. Therefore, in this study, DNA barcoding was carried out targeting the mitochondrial COI gene. Molecular analysis confirmed that the collected egg and larvae belonged to the B. mollis species due to their high identity (>99%) with reference to previously submitted adult B. mollis sequences in the GenBank. Phylogenetic analysis showed a closer evolutionary relationship among B. mollis and B. splendens than with B. decadactylus. To the best of our knowledge this is the first genetic and morphological confirmation of B. mollis egg and larvae worldwide and suggests the southwest coastal area in Sri Lanka, in the north central Indian Ocean, as a potential spawning ground for this species.

Polychaetes (Phylum Annelida) respond to sensory stimuli through the usage of sensory organs and appendages, such as palps, which vary in shape and structure depending on lifestyle. The typical palps of nereidid polychaetes are tapered appendages constituted by two articles. The palpophore is the wider and longer basal article, followed by the thinner and shorter palpostyle that contains the majority of sensory cells. Previous studies on Hediste diversicolor palps were focused on these sensory cells. To achieve a more comprehensive view of the histology and ultrastructure of the palps, H. diversicolor specimens were collected from the northern Portuguese Atlantic coast and the palps were processes for light (semithin sections) and transmission electron microscopy. The current study revealed details of the cuticle, which is thinner in the palpostyle than in the palpophore. Five types of secretory cells were distinguished mainly based on the characteristics of their secretory vesicles. Two of these types could be classified as protein-secreting cells, and the other three as mucus-secreting cells. Granulocytes and eleocytes were found in the celom cavity of the palps. The latter contained lipid droplets and a very large amount of glycogen. In the central region of the palpophore, a ring of muscle cells responsible for the retraction of the palpostyle encircled the main palp nerve. The latter was formed by numerous axons and glial cells containing bundles of filaments and gliosomes.

Many ascidian (sea squirt) species are common members of fouling communities, particularly on floating substrates such as docks and pilings and through maritime transport, have been introduced worldwide. For the past 30 years, marinas in Southern California have been regularly monitored for introduced species due to their proximity to the international shipping terminals in Los Angeles and Long Beach Harbors. Here, we report on the first record in the eastern Pacific of an ascidian in the family Corellidae (O. Phlebobranchia), Corella japonica, found at the Newmarks Yacht Centre in Los Angeles Harbor. This study further highlights the importance of continuously monitoring harbors and marinas to detect the early arrival of new non-native species.

Fjord ecosystems serve as crucial habitats for elasmobranchs, supporting them across all life stages. Chilean Patagonia provides one of the most complex and extensive networks of fjord ecosystems in the world, displaying high marine biodiversity, including elasmobranchs. However, little is known about this ecologically important group of fishes in these ecosystems. This study investigates the biodiversity of elasmobranchs in the Comau Fjord over a period of 6 months by combining morphological and molecular data. In total, 309 specimens within a radius of 7.5 km were recorded, belonging to six families and nine species: Hexanchus griseus (77.5–178 cm LT), Notorynchus cepedianus (180.6 cm LT), Schroederichthys bivius (35–65.2 cm LT), Scymnodon macracanthus (37.3 cm LT), Centrophorus squamosus (87.4 cm LT), Deania calceus (58.3–98.6 cm LT), Squalus acanthias (25.5–101.1 cm LT), Dipturus chilensis (62.9–152 cm LT), and Dipturus trachyderma (69.8–194 cm LT). This included records of three species previously unknown in the fjord and was equivalent to nearly 20% of the elasmobranch richness found in Southern Chile. The results further suggest that the Comau Fjord could be a primary nursery ground for several species of elasmobranchs. This is the first time that a species inventory of elasmobranchs is conducted in a Chilean fjord system. The outcomes of this research provide an elasmobranch species checklist with biological aspects from the Comau Fjord, which are essential data to inform decision makers, conservation managers, and future research.

Calcifying macroalgae play a critical role in coastal ecosystems, but rising sea temperatures pose a significant threat to their survival. This study aims to investigate the thermal sensitivity of the three marine macroalgal species Padina boryana, Halimeda opuntia, and H. macroloba. Photosynthetic performance, metabolism, pigment content, and oxidative stress–related parameters were measured at temperatures of 28°C, 32°C, 36°C, and 40°C and the thermal performance curves (TPCs) were determined for Fv/Fm, Fv/F0, ϕPSII, and oxygen production to assess maximum rate (Rmax), optimum temperature (Topt), critical thermal maximum (CTmax), and thermal safety margin (TSM) of these three macroalgal species. The results showed that 40°C had the most negative effect on all three species with P. boryana demonstrating better performance compared to both Halimeda species. TPCs from photosynthetic performance revealed thermal sensitivity variations by species and P. boryana exhibited a broader thermal tolerance range compared to Halimeda. On the other hand, TPCs of oxygen production provided similar CTmax values. Based on TPC projections, all three species might survive future ocean warming and marine heatwaves, though these conditions will have significant effects, with P. boryana showing greater tolerance than both Halimeda species. This study highlights the differential thermal responses and sensitivities of these macroalgae, contributing to understanding their potential resiliencies under future climate change scenarios.

The present study describes a new Mediterranean terebellid, Spinosphaera latachaeta sp. nov., found along the Aegean coast of Türkiye and the Sea of Marmara, between 27 and 80 m depth in soft substrata. It can be morphologically distinguished from all other species of Spinosphaera having 18 pairs of notopodia, double rows of uncini present until the last notopodia, and 11 pairs of Spinosphaera-chaetae. A dichotomous taxonomic key and a table summarizing the morphological characters that distinguish all species of Spinosphaera are provided. This study also reports, for the first time, the transformations of Spinosphaera-chaetae and saw-like chaetae from the anterior to posterior segments of body.

ZooBank: urn:lsid:zoobank.org:pub:628B1F01-166A-4E26-9C42-39D0CBFDE998.

We document the first recorded nesting attempt by a green sea-turtle (Chelonia mydas) in Pemba located in the Cabo Delgado Province of northern Mozambique – an urban area with a population of 200,529 inhabitants. This sighting expands the known nesting range of sea-turtles by 40 km south of the Quirimbas Archipelago, highlighting Pemba’s potential as a critical nesting site. In July 2021, local fishermen were observed by a tourism operator killing the turtle and selling its meat. Consequently, the absence of eggs at the presumed nesting site suggests that the turtle was intercepted before it could lay eggs. This incident highlights the threats to sea-turtles and the need for conservation while emphasising the importance of collaboration among communities, government, and researchers to protect nesting activity.

In the Caribbean Sea, orcas (Orcinus orca, also known as killer whales) are present throughout the year. The most recent review confirmed seven strandings of the species in the Caribbean Sea in the period May 1851 to January 2023, all of which were single strandings and only one of which occurred in Venezuela. In this publication we document the circumstances of the successful rescue, by local fishers and authorities, of seven orcas that stranded in August 2023 on the coast of the State of Sucre, north-eastern Venezuela. Worldwide, this is only the second mass stranding of the species within the tropics (23.5°N to 23.5°S). We also documented the presence of a probable whalesucker (Remora australis) on a juvenile orca. The present case represents the first mass stranding event of orcas in Venezuela and the Caribbean Sea and only the second in a tropical location worldwide.

We report the first non-indigenous dottyback Pseudochromis persicus record in the Mediterranean Sea. A single individual was documented several times at the same location on October 2024 in Bat Galim reef, a shallow rocky shelf of Rosh Carmel underwater ridge on the northern coast of Israel. This record represents the first sighting of Pseudochromidae, a family native to the Indo-Pacific Ocean, in the Mediterranean Sea. It is also the first record of P. persicus beyond its native range in the Persian Gulf and the Arabian Sea.

Members of the genus Actinia are familiar members of rocky shore communities across much of the world. However, to date, no Actinia species have been reported from the North American continent. Here, we report Actinia from an approximately 22 km length of the New Jersey, US shoreline, where it was first discovered in 2021. Morphology and DNA barcoding data (mitochondrial cytochrome c oxidase I and nuclear internal transcribed spacer) indicate that these populations are Actinia equina. The presence of these populations close to major ports in New Jersey, New York, and Philadelphia suggests a probable introduction from shipping activities.

This study investigates the reproductive biology of Holothuria arguinensis over one year (December 2016 to December 2017) from two locations on the Atlantic coast of Morocco: Skhirat (North Atlantic) and Souiria K'dima (Central Atlantic), including the sex ratio, size at sexual maturity, and reproductive cycle. Monthly sampling was carried out, along with the collection of environmental and biometric data at each site. The sex ratio did not differ significantly from 1:1 at either study site. The gonadosomatic index (GSI) reached its peak during spring (April and May) for both sexes, and the spawning period was observed from summer to autumn (June–October) at both locations, suggest annual spawning. GSI was correlated with increasing or high chlorophyll-a concentrations, salinity, and spawning with rainfall periods. The estimated size at sexual maturity was 15.9 cm body length, 189.1 g total body weight, and 92.5 g gutted body weight. The minimum mean oocyte diameter was recorded during the recovery stage (31 ± 11 μm (mean ± SD) at Skhirat and 34 ± 23 μm (mean ± SD) at Souiria K'dima), while the highest values were observed in the partial spawning stage (112 ± 27 μm (mean ± SD) at Skhirat and 104 ± 19 μm (mean ± SD) at Souiria K'dima). This study highlights the need for further research to expand our knowledge of the biological and ecological characteristics of H. arguinensis populations, to facilitate the cultivation of juveniles in captivity, and to develop fishing regulations based on scientific findings. As a fishery management strategy, we suggest a closed season from April to October to protect the reproductive period of H. arguinensis on the Moroccan coast.

In this study, a single specimen of Pacific black scabbardfish Aphanopus arigato Parin, 1994 was collected at a depth of ~500 m near Dongsha Island in southwestern Taiwan (18°49′ to 20°45′N and 112°46′ to 116°15′E), on 14 March 2023. This is the southernmost record of A. arigato, with a significantly wide range extension from northern Japan, and southern Kuril Islands to the South China Sea. We also provide comparisons of the morphological measurements, first description of sagittae otoliths, and a partial sequence of the cytochrome oxidase subunit I gene for the specimen studied in this study.

Ionella fimbriata sp. nov. is described from a pair of bopyrid isopods attached to a male specimen of the ghost shrimp Neocallichirus grandimana collected in Veracruz, Mexico. This is the fifth species belonging to Ionella but the first one recorded from the Atlantic Ocean, which represents an important extension of its distribution range because until now all Ionella species were known from the Pacific Ocean. Females of I. fimbriata sp. nov. can be differentiated from the others of the genus by a barbula with one stout, acute, falcate projection on each side and medial margin with triangular rounded projections; seven pairs of pereopods with elongate cuticular extensions on bases and ischia, and five pairs of tuberculated biramous pleopods of pinnate shape. Males can be recognized by five pairs of globose biramous pleopods, in which endopods are longer than exopods, and uropods longer than pleopods. Description and illustrations of both the female and male I. fimbriata sp. nov. are provided, as well as keys for both sexes of all species in the genus. The fecundity, embryo size and volume of I. fimbriata sp. nov. are reported.

While the giant anemone, Relicanthus daphneae, has been described as a characteristic inhabitant of the East Pacific Ocean since 1991, there are relatively few published occurrences worldwide. Here, we present the discovery and molecular verification of R. daphneae along the southern Central Indian Ridge, at the Rodriguez Triple Junction, and along the northern Southeast Indian Ridge within the BGR contract area for the exploration of marine massive sulphide deposits in the Indian Ocean. Individuals were solitary and attached exclusively to basalt hard substrates on the periphery of hydrothermal vent fields, at distances from active vents between 66 and 710 m. We report megafauna observed in close proximity to R. daphneae and, in one case, polychaetes on its tentacles and oral disc. For the first time, the giant anemone was observed capturing prey, a shrimp of the species Rimicaris kairei. Beyond this remark on the diet of these anemones, we also report other behavioural aspects for this species.

Morphological and molecular methods were used to describe a new species of Trapania Pruvot-Fol, 1931 from shallow water kelp forests on the north-central coast of Peru. The new species, Trapania huarmeyana sp. nov., is distinguished from other species along the Eastern Pacific by external morphological characters such as its translucent white body with brown stripes and small spots on the dorsum, blotches on the base of the extra-branchial processes, extra rhinophoral processes and gill branches. Internally, T. huarmeyana sp. nov. is distinguishable by several morphological characteristics of the radula, jaws and genital organs. Phylogenetic trees recovered using Bayesian Inference and Maximum Likelihood analysis of DNA sequences support its distinct status and clarify its relationship to other species from the Eastern Pacific. This new species constitutes the first record of Trapania from the Humboldt Current Ecosystem, contributing to our understanding of the distribution of the genus in the South-eastern Pacific.