Cryptic species in coral reefs, such as sea slugs, represent an important portion of their biodiversity, which is usually underestimated. Autonomous Reef Monitoring Structures (ARMS) have been implemented to estimate cryptic diversity in coral reefs. Therefore, this research aimed to contribute to the southern Gulf of Mexico (GM) and the Caribbean Sea (CAR) coral reefs’ sea slugs’ diversity and distribution using ARMS as a collection method. Fifty-eight ARMS were placed at three coral reefs in the GM and CAR, recovered after 1–2 years and then, disassembled at the laboratory. Plates were individually placed in trays with seawater, where we searched for sea slugs. A total of 242 organisms were found belonging to 31 species; 20 of them were identified to the species level, while 11 were determined up to genus or family. More than half of the species (19) were found in Bajo de 10 (GM), while 15 species were found in the CAR localities. Unlike previous studies, we assessed sea slugs’ diversity exclusively by an indirect sampling method. In this work, we found 9.4% of the sea slug diversity recorded in the Caribbean, and we report four determined species for the first time in the country. New records of species, and even one family for the GM stress the gap of information that we still need to fulfil in the area. We recognize ARMS as a useful tool to find juvenile, cryptic and rare species of sea slugs, as well as to standardize their quantification and record their diversity.

The spiny butterfly ray Gymnura altavela (Linnaeus 1758) is classified as Endangered by the International Union for Nature Conservation (IUCN) and considered Critically Endangered in the Mediterranean Sea and South-west Atlantic. Despite its status, few studies on the population biology and genetics for the species are available, undermining conservation efforts. In the present study, we evaluated the taxonomic status of Gymnura altavela along both sides of the Atlantic using COI sequences. Our genetic data support the existence of two genetically differentiated G. altavela lineages (West and East Atlantic) and further studies are required to evaluate the hypothesis that these lineages could, in fact, be cryptic species within this endangered batoid's genus.

We present the description of a new species of genus Timea and the re-description of T. hechteli from cryptic habitats in the Gulf of Mexico. Timea alcoladoi sp. nov. is an encrusting, pale orange sponge, with megascleres ranging from styles to subtylostyles (185–990 μm long) and a single category of microscleres, spherostrongilaster characterized by a prominent rounded centre (5–15 μm in diameter). Timea hechteli was established by Lehnert & Heimler, based on the description of a very small specimen, previously recorded as Halicometes stellata by Little, and transferred to the genus Timea by Hechtel. However, because the name ‘stellata’ was preoccupied by the type species, T. stellata, the species was renamed T. hechteli, to honour George Hechtel. After the revision of Little's material and new material, we present the re-description of T. hechteli. For both species, partial sequences of COI mtDNA and ITS1-5.8S-ITS2 rDNA region were obtained in order to complement our morphological taxonomy and establish their molecular systematic position among tethyids. Tree topologies for both loci were congruent by grouping together our species as a sister group of the main Tethyida clade, which is according to the current systematics of the group. The COI fragment showed Timea as polyphyletic due to two sequences of Timea (from GenBank) that were clustered with other sponge groups. The species described here are the first record of the genus Timea from the Mexican coast of the Gulf of Mexico. A taxonomic key for West Atlantic Timea species is also presented.

The mojarras (Eucinostomus) are a widespread group of coastal fishes of controversial taxonomy because of similarities in their external morphology. In the present study, we assessed the genetic diversity of species and populations of Eucinostomus using DNA barcodes using a systematic and phylogeographic context. In total, 416 COI sequences of all valid Eucinostomus representatives were analysed based on public databases and collected specimens from the north-eastern coast of Brazil (Western South Atlantic). Several cases of misidentification were detected in the barcode dataset (E. argenteus, E. harengulus, E. gula, E. dowii and E. jonesii) that could account for the taxonomic issues in this genus. In contrast, we identified four molecular operational taxonomic units (MOTUs), with divergence above 2% in the Western Atlantic, that correspond to cryptic forms within E. argenteus, E. harengulus, E. gula and E. melanopterus. These data suggest that Plio-Pleistocene events (rise of the Panama isthmus, Amazonas outflow and sea-level fluctuations) played a major role in the diversification of mojarras. While subtle morphological differences have been used as proxies to discriminate Eucinostomus species, the genetic data proved to be efficient in differentiating them and revealing potentially undescribed taxa. Therefore, we recommend that further taxonomic studies in mojarras should incorporate DNA-based evidence.

Clathria is one of the most species-rich genera among Demospongiae, but only nine species have been recorded so far from Brazil. Here we describe a new species of Clathria (Microciona) collected by trawling in waters of Sergipe State (north-eastern Brazil). The new species is differentiated from other encrusting Clathria with a hymedesmioid skeleton by the possession of a combination of long thin subectosomal subtylostyles, two category sizes of acanthostyles, both erect and echinating the basal spongin skeleton, long slightly curved choanosomal principal subtylostyles with tuberculate spine heads and wing-shaped toxas as microscleres.

A new species of eurysquilloid stomatopod, Eurysquilla petronioi sp. nov., is described from the tropical western Atlantic. Eurysquilla petronioi sp. nov. is the fourteenth species of the genus to be recognized worldwide, the fifth species from the western Atlantic and the second from Brazilian waters. It is most closely related to E. maiaguesensis from Puerto Rico, but differs chiefly in having an unarmed versus apically spinous rostral plate and 6 or 7 rather than 8–10 teeth on dactylus of raptorial claw. A key to the species of the genus is provided.

The family Thorectidae includes 23 valid genera and 130 species, characterized by the presence of laminated fibres and diplodal choanocytye chambers. Currently the genus Thorecta comprises approximately 20 valid species, distributed mainly in the Indo-Pacific. We describe here a new species of Thorecta that is the only valid species of the genus described in the Atlantic Ocean so far. Samples were collected by trawling on board of the RV ‘Astro Garoupa’ in Potiguar Basin, on the northern coast of Rio Grande do Norte State, north-eastern Brazil. Thorecta atlantica sp. nov. is greyish-brown to dark brownish-grey and presents a distinctive globular or clavulate shape, with 1–2 large apical oscules that open to deep atria. It was found between 61 and 160 m depth. A literature survey suggests that many species referred to Thorecta should be relocated to different genera due to absence of diagnostic characters, and that the genus Thorecta should group only 11 species: T. carteri, T. marginalis, T. prima, T. lata, T. farlovi, T. meandrina, T. polygona, T. reticulata, T. tuberculata, T. vasiformis and T. atlantica sp. nov. The tortuous history of the genus is an example of the damage that poorly-described species can cause to classification. Detailed descriptions of fresh material, well illustrated by photographs and including as many characters as possible, are essential tools for the clarification of the systematics of Thorecta in the future.

The present contribution reports for the first time the sessile barnacle Xenobalanus globicipitis as an epizoic of the striped dolphin Stenella coeruleoalba in the oligotrophic waters of north-eastern Brazil. One barnacle specimen was found on a dead cetacean in Ceará State, north-eastern Brazil. Diagnosis and figures of the barnacle are provided and the relationship between the epizoic and the host discussed.