A new species of polychaete annelid, Armandia ramanamurthyi n. sp., is described from the sandy sediments off Tamil Nadu coast, Bay of Bengal, northern Indian Ocean. The major feature distinguishing A. ramanamurthyi n. sp. from other species of the genus is bearing a non-papillated anal tube and the presence of a bulbous, orbicular papilla ventrally placed at the proximal end of the anal tube. The orbicular papilla bears black pigmentation and posteriorly ends in an oblique cirrus. Additionally, Ophelina arabica Parapar, Al-Kandari, Barroso & Moreira, 2023 described from Kuwait waters is recorded for the first time in Indian waters since its original description.

Cheilopogon arcticeps (Günther, 1866) is recorded for the first time from the Indian coastal waters. Two specimens of C. arcticeps (158–167 mm SL) were collected from the Petuaghat fishing harbour of Purba Medinipur, West Bengal, India. The present paper reports the species for the first time from Indian waters and thus, the distributional range of the species is extended from Western Pacific Ocean to the Bay of Bengal, Indian Ocean. This paper provides more detailed information on the taxonomy and morphometric of the poorly known species.

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.

The amphipod Ampithoe bizseli Özaydinli and Coleman, 2012 is a cryptogenic species that was recently described in Turkey. Although to date it has only been recorded in the Mediterranean Basin, it is potentially native to the Red Sea and Indian Ocean. During a macrozoobenthos sampling campaign carried out in the Canary Islands in 2023, 25 individuals of A. bizseli were found in association with some fish farm facilities. This work represents the first report of this amphipod in European Atlantic waters and increases knowledge of the ecology of this non-indigenous species.

We report on four brachyuran crabs collected from the carapaces of loggerhead sea turtles Caretta caretta nesting on Yakushima Island in Kagoshima prefecture, Japan. Three of these crab species have not been previously reported as epibionts on sea turtles. Our research suggests that physical damage to a turtle's carapace, such as cracks and holes created by other epibionts like the burrowing barnacle Tubicinella cheloniae, can create unique habitats for these opportunistic crabs.

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.

In many species with encapsulated larval development, the larvae play an active role in hatching. However, the factors that control when the larvae hatch from each egg-capsule within an egg-mass are largely unknown. Advanced egg-masses of the gastropod Crepipatella peruviana were used to determine the hatching time of capsules from each egg-mass. After each female was detached, the egg-mass was also removed from the substrate and all capsules were then counted and measured. All capsules were examined to determine the time of hatching and the order in which capsules hatched from each egg-mass. Larvae were collected from each hatched egg-capsule and the number, size and weight of larvae from each capsule were determined. After 50–60% of the capsules from each egg-mass had hatched, the same characteristics of the remaining unhatched larvae from sister capsules were documented. Larvae were found to have hatched when they reached a size of 354 ± 22 μm (n = 245). Larvae from capsules within the same egg-mass hatched over a period of up to 12-days. The order of hatching in capsules from the same egg-mass was determined by larval content: capsules with fewer larvae and smaller capsules with heavier larvae hatched first. The hatching from one capsule in any given egg-mass did not induce the hatching of its sister capsules. Furthermore, hatching also occurred successfully in the mother absence, suggesting that this process is largely or completely controlled by the encapsulated larvae, although a possible maternal role in synchronizing hatching cannot be excluded.

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.

Azooxanthellate corals of Rhizangiidae, with their distinctive morphological and ecological features, are widely distributed across global oceans but remain under-studied due to identification challenges. Comprehensive underwater surveys across diverse marine habitats such as rocky reefs and submerged shipwrecks were undertaken, and findings highlighted the exclusive presence of Culicia stellata in natural rocks, off the coast of Kaup for the first time in Indian EEZ. The study also records the presence of Cladangia exusta, nearly six decades after the first record from off Cochin, Laccadive Sea. This research presents a detailed study of the taxonomic description, distribution, and ecological preferences of Cladangia exusta and Culicia stellata in the Laccadive Sea. This study underscores the importance of accurate species identification for effective conservation strategies and enriching biodiversity records.

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.

Although nudibranchs are common and attractive animals, our understanding of these marine gastropods in Vietnam remains limited. Prior research has suggested that combining morphological examination with molecular analysis results in more accurate identification of nudibranchs. However, previous studies in Vietnam have typically relied solely on morphological methods for nudibranch identification. In this study, the nudibranch species Halgerda batangas was recorded in Vietnam for the first time based on both morphological and molecular approaches. Halgerda batangas was characterized by a network pattern consisting of orange lines, relatively low dorsal tubercles with red-orange caps and white basal rings, and an orange line along the foot margin. Molecular analysis corroborated the morphological findings. These results suggest that integrating morphological and molecular methods is an effective approach for identifying nudibranchs.

The yellownose skate (Dipturus chilensis) and roughskin skate (Dipturus trachyderma) are the only two elasmobranch species targeted by commercial fishing operations in Chile. Despite their importance, much of their biology and ecology remain poorly understood. This research aimed to evaluate the feasibility of tagging these species. In 2021, a pilot study was conducted at two locations, utilizing Petersen discs, acoustic transmitters, and pop-up satellite transmitters on both species. The results revealed a 6% recovery rate from the 50 skates tagged with Petersen discs, while 29.4% of those tagged with acoustic transmitters were successfully detected. Additionally, data from all ten satellite transmitters were successfully transmitted and recovered. The results revealed a maximum horizontal movement of 35.9 km, with the duration of liberty ranging from 8 to 275 days. Stocks of both species are currently depleted, and fishery management relies on closures and total allowable catches, where fishing effort is concentrated in short spatial and temporal windows. These particularities present significant challenges for implementing a national tagging programme, especially in terms of tag recovery. The main conclusion of this research is that the implementation of a tagging programme for both species is feasible. Satellite tagging provides the best results, but its higher implementation cost and limitations in use for relatively small skates could be mitigated by combining it with Petersen discs. Establishing a long-term tagging programme is essential for enhancing the understanding of distribution and migration patterns, which is crucial for enhancing conservation and management efforts for these skates in Chile.

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.

Egg masses of Aplysia depilans consist of long and intertwined strings containing numerous capsules with eggs. Light microscopy stains and transmission electron microscopy revealed four layers in the gelatinous sheath that encircled and aggregated the chain of egg capsules. The outermost layer has a fluffy structure. The second, third, and fourth layers consisted of reticulated matrices with different densities. The second and third layers were divided into 5‒6 strata each. The fourth and innermost layer of the gelatinous sheath has a higher density and no visible stratification. This layer glues the tightly packed capsules to one another and to the outer layers of the gelatinous sheath. The thin wall of the capsules is formed by a homogeneous and highly electron-dense material. Inside the capsules, the eggs or embryos were bathed in an electron-lucent aqueous medium. Bacteria and diatoms were the most abundant microorganisms on the surface of egg strings. Bacteria penetrate the gelatinous sheath and appear to be involved in the degradation of the upper strata, but were never found inside the egg capsules. Metagenomic analysis revealed a large taxonomic diversity of bacteria associated with egg masses of A. depilans. Although 15 phyla could be recognized, the families Flavobacteriaceae (Bacteroidota), Lentisphaeraceae (Lentisphaerota), and Rhodobacteraceae (Pseudomonadota) represented 67.9% ± 11.6% of the relative abundance in the microbiome of the egg string samples. The presence of genera capable of decomposing polysaccharides, such as Tenacibaculum and Cellulophaga, supports the idea that bacteria are responsible for the degradation of the gelatinous layers of the egg strings.

Oysters have unique life history strategies among molluscs and a long history in the fossil record. The Ostreid form, particularly species from the genus Crassostrea, facilitated the invasion into intertidal, estuarine habitats and reef formation. While there is general acknowledgement that oysters have highly variable growth, few studies have quantified variability in oyster allometry. This project aimed to (1) describe the proportional carbonate contributions from each valve and (2) examine length–weight relationships for shell and tissue across an estuarine gradient. We collected 1122 C. virginica from 48 reefs in eight tributaries and the main stem of the Virginia portion of the Chesapeake Bay. On average, the left valve was responsible for 56% of the total weight of the shell, which was relatively consistent across a size range (24.9–172 mm). Nonlinear mixed-effects models for oyster length–weight relationships suggest oysters exhibit allometric growth (b < 3) and substantial inter-reef variation, where upriver reefs in some tributaries appear to produce less shell and tissue biomass on average for a given size. We posit this variability may be due to differences in local conditions, particularly salinity, turbidity, and reef density. Allometric growth maximizes shell production and surface area for oyster settlement, both of which contribute to maintaining the underlying reef structure. Rapid growth and intraspecific plasticity in shell morphology enabled oysters to invade and establish reefs as estuaries moved in concert with changes in sea level over evolutionary time.