Since the taxonomic revision of the Ophidiasteridae by H.L. Clark (1921), in which 20 genera were recognized as valid, several new genera and species were included in this family, and the boundaries between some of them became largely arbitrary. This also applies to Narcissia Gray, 1840, whose morphology and taxonomy are still very poorly understood today. The main goals of this research were: review the taxonomy of the genus Narcissia, from morphological studies; redescribe N. trigonaria Sladen, 1889 s. str.; characterize N. canariensis (d'Orbigny, 1839) and N. gracilis A.H. Clark, 1916, the two valid species most similar to N. trigonaria; review the validity of N. ahearnae Pawson, 2007 and N. trigonaria var. helenae Mortensen, 1933; review the validity of N. gracilis malpeloensis Downey, 1975. Altogether 370 specimens were analysed. All morphological structures of taxonomic importance have been illustrated, and, for the first time, the internal characters of this group were studied, from electron microscopy and microtomography. A new diagnosis for the genus Narcissia was constructed. Narcissia trigonaria was redescribed from a large specimen, from the type locality (Bahia, Brazil). Narcissia ahearnae is considered a valid species, and N. canariensis and N. trigonaria distinct entities. Narcissia trigonaria var. helenae is placed in the synonymy of N. trigonaria, and N. gracilis malpeloensis into the synonymy of N. gracilis. The dataset obtained in this work is by far the most complete acquired for the genus Narcissia.

Germination of cysts serves as inoculum for the proliferation of some dinoflagellates, and cyst abundance in sediments represents crucial information to understand and possibly predict Harmful Algae Blooms (HABs). Cyst distribution is related to the physical characteristics of the sediments and the hydrodynamics (circulation) of a particular region. In the northern Gulf of California (nGC) several Gymnodinium catenatum HABs have been recorded. However, the presence of resting cysts and the effect of hydrodynamics on their distribution in the nGC have not been investigated. This study evaluated cyst abundance, distribution and their relation to local circulation in surface sediments during two periods that coincided with a non-bloom year condition (July 2016) and after a major HAB registered in the nGC that occurred in January 2017. Also, a numerical ocean model was implemented to characterize the transport and relocation of cysts and sediments in the region. Gymnodinium catenatum cysts were heterogeneously distributed with some areas of high accumulation (as high as 158 cyst g−1, and 27% of total cyst registered). Cysts seemed to be transported in an eastward direction after deposition and accumulated in an extensive area that probably is the seedbed responsible for the initiation of HABs in the region. The nGC is a retention area of cysts (and sediments) that permit the formation of seedbeds that could be important for G. catenatum HAB development. Our results provide key information to understand G. catenatum ecology and specifically, to understand the geographic and temporal appearance of HABs in the nGC.

Invasive species are leading to ecosystem changes and socioeconomic deterioration around the globe. In 2018, unknown soft corals were noticed forming a massive ‘blue carpet’ on a shallow reef environment at Todos os Santos Bay, South-west Atlantic. In this study we identified the species, quantified their distribution and abundance as a first step for baseline invasion monitoring, and discussed origin, vector and impacts on native competitors. Coral samples were identified based on morphology and a multilocus DNA barcode, and benthic structure was characterized using digital photoquadrats. Our results revealed two new harmful non-native octocorals in this tropical rocky reef, the ‘blue polyps’ genus Sarcothelia (Xeniidae), native to Hawaii but likely an undescribed cryptic species, and Briareum hamrum (Briareidae), native to the Indian Ocean. Sarcothelia sp. was the dominant taxon in the rocky reef (mean cover 23.66% ± 21.46), exhibiting high coverage as well in the sandy and patch reef habitats (15.83% ± 15.81), however, only three colonies of B. hamrum were found, all outside the sampling area. These octocorals were in physical contact with native benthic organisms, mainly with the most abundant group, but apparently avoid turf algae in sandy and patch reef habitats. We suggest that irresponsible marine aquarium releases likely introduced these species to Brazilian reefs. After identifying the aquarium trade as the main vector of octocoral introductions, we reinforce the importance of inspecting marine species importation and the urgent need to implement a government plan to mitigate invasive species' impacts on the natural reefs of Brazil.

Bioluminescence is widespread in the marine environment. The bioluminescence of some species of the fireworm Odontosyllis (Annelida: Syllidae: Eusyllinae) has been well studied, although the presence or absence of bioluminescence in most species of this genus is yet to be revealed. The bioluminescent worms were observed after sunset around the new moon day in July and October 2020 and in July to October 2021 in Nagasaki Prefecture, Japan. Molecular phylogenetic analysis based on two mitochondrial and one nuclear gene sequence showed that the worms were closely related to Odontosyllis australiensis, but the partial 16S rRNA gene sequences differed by 2% between those of the Japanese and Australian material. Because only epitokes, i.e. morphologically modified sexually mature worms, were collected, further studies on morphological characters of atokes would be required in the future. We therefore tentatively refer to them as Odontosyllis cf. australiensis. Molecular phylogenetic analysis also showed that known bioluminescent Odontosyllis species belong to various lineages.

Lacydonia Marion & Bobretsky, 1875 is the sole genus in the family Lacydoniidae Bergström, 1914. We herein describe the new species of Lacydonia shohoensis sp. nov. from 2042-m deep bottoms at Shoho Seamount of the Nishi-Shichito Ridge, the Northwest Pacific Ocean. It is most similar to L. anapaulae Rizzo et al., 2016 in having a depression on the median anterior region and lacking lateral lobes on the posterior margin of prostomium whereas it is distinguished by possessing pygidium dorsally pigmented with three reddish spots and non-pigmented pygidial lateral cirri equally elongated.

The population dynamics of the stout reef octopus, Octopus insularis fished with longlines of pots in mid-shelf waters of north-eastern Brazil was studied based on fishermen's logbooks and onboard monthly fishing trips from September 2009 to August 2010. Specimens marked with oxytetracycline kept in tanks for up to 21 days provided evidence of the daily deposition of growth increments in the lateral wall of the upper beaks. Sampled specimens weighed 50–1280 g and had 43–172 daily growth increments. Compared with congeneric species from higher latitudes, O. insularis grows faster and has a shorter longevity in the north-eastern Brazil tropical environment. Total catches and catch-per-unit effort were substantially higher in the dry season, with less wind and cooler temperatures. The presence of larger specimens was seasonal, correlated with the chlorophyll-a levels recorded six months earlier. The year-round presence of mature females and males, spawned females, and egg masses attached to the pots, were considered evidence of migration of small and young specimens from coastal areas towards the 20–40 m depth range for reproduction. Annual landings attained ~200 tonnes (2005–2010). Although recent landing statistics are missing, fishermen interviewed in 2021 claimed that the fishery was still profitable. It is suggested that, despite the lack of management, the fast growth, year-round reproduction and limited market for this relatively small octopus, prevented the fishery from collapse and reinforces the current view of the high resilience of cephalopod fisheries.

Dirivultid copepods (Siphonostomatoida), one of the most successful meiobenthic organisms found at deep-sea hydrothermal vents, have been the focus of most previous ecological studies among meiofauna in these habitats. The ecology of Harpacticoida, a major benthic copepod group in typical deep-sea floor, however, is not well understood in terms of variations in community structure and controlling factors at venting sites. The spatial heterogeneities in benthic harpacticoid composition and their association with environmental parameters were investigated at hydrothermal vent chimney structures in the calderas of three neighbouring sea knolls (Bayonnaise Knoll, Myojin Knoll and Myojin-sho Caldera) in the western North Pacific. While a previous study had reported the distribution of dirivultids was strongly associated with spatial differences in stable carbon isotopic signatures (δ13C) of organic matter in the detritus on active chimneys in the field, multivariate analyses detected no significant corelation between the parameter and harpacticoid composition in this study. Instead, high associations of the harpacticoid composition with differences in water depth and total organic carbon (TOC) concentration were detected. Ectinosomatidae dominated at vent sites with lower TOC values in the shallowest Bayonnaise Knoll, while they were less prevalent at deeper vent fields in the other knolls, where Miraciidae was the most abundant family. This study indicated the availability of vent chemoautotrophic carbon is not a primary factor controlling the composition of harpacticoids even in the habitats on the hydrothermal vents, but instead by the food amount, regardless of its resources (including marine snow from the sea surface), in the study area.

We examined the prevalence and shell use of two species of hermit crabs (Pagurus granosimanus and Pagurus beringanus) in exposed and protected microhabitats at five sites in the rocky temperate intertidal on San Juan Island, Washington, to compare present habitat partitioning and potential interspecific competition to that reported nearly 50 years ago. We found that, in contrast to previous findings, the two species of hermit crabs overlapped extensively at some sites, typically those with less wave action. While the hermit crabs typically inhabited certain types of shells significantly more than others, and that use was congruent across microhabitats and species of hermit crabs at the same site, the dominant domicile differed substantially across sites. We provide a more complete ranking of shell use than previous authors and note site-specific dominant shell use. We conclude that previous habitat partitioning by depth may have weakened at protected sites. We hypothesize that increasing temperatures have caused P. granosimanus to expand its range deeper into the intertidal, which may increase the degree of interspecific competition for shells at the edge of the species’ tidal height range, where they overlap. Whether the habitat shift by this hermit crab is due to recent alterations in climate (particularly elevated temperatures, ocean acidification and lower local open ocean salinity) is unknown, but warrants further study.

Marine capture of Sphyraena putnamae along western Bay of Bengal has been increasing. Owing to scarcity of information available on feeding dynamics globally, the present study was conducted using 763 individuals captured during 2017–19, to decipher trophic ecology and relationships. Of the individuals analysed, 54.8% had their stomachs either empty or with trace amounts of food, 27.3% had part-full stomachs and 18.0% had full stomachs. Stomach vacuity and fullness as well as predator–prey weight ratio varied with increase in body size, implying higher feeding intensity in large-sized fishes. Feeding activity was highest during July–November and lowest during March–April. The species is an opportunistic piscivorous pelagic predator that feeds on teleosts (>85%) and cephalopods. Sardines were the major prey, followed by whitebait, squid, bigeye scad, Indian scad, silverbellies and Indian mackerel. Diet contents were similar between sexes (82.17%); however, it varied among seasons (56.86–69.85%). Shifts in prey preferences from sardines, squid and bigeye scad to ribbonfish, shad, grunter, Indian mackerel, horse mackerel and Acetes were observed with increase in fish size, and diet varied between individuals sized <60.0 and >60.0 cm. Trophic level value was 3.51 ± 0.13 and Levin's Standardized Niche Breadth Index was 0.21. Dietary niche breadth varied across seasons and sizes, with higher values during summer and winter (0.36–0.41) and in fish measuring >45.0 cm (0.50–0.68), which implies generalized feeding behaviour. The present study represents the first detailed report on the diet of S. putnamae and will provide a substantial contribution to stock management through understanding of trophic interactions.