Autonomous reef monitoring structures (ARMS) have been proposed as a standardized, passive, nondestructive sampling tool. This study assessed the ability of ARMS to capture the cryptic species diversity of two coral reefs by recording species richness and taxonomic representativeness using conventional taxonomy. The capacity of ARMS, as artificial substrates, to favor the establishment of nonindigenous species over native species was also evaluated. The use of ARMS allowed the detection of 370 species morphotypes from nine phyla, yielding 13 new records of geographic distribution expansion, one exotic species for the Gulf of México and the Caribbean Sea, and six newly described species. It was also possible to make spatial comparisons of species richness between both reefs. ARMS captured cryptic diversity exceptionally well, with the exception of echinoderms. Furthermore, these artificial structures did not hinder the colonization ability of native species; in fact, the colonization patterns on the structures themselves represented the spatial differences in the structure of benthic assemblages. This study represents the first effort to make a conventional taxonomic description of the cryptic fauna of the Yucatan Peninsula using ARMS. It is recommended to assess coral reef species diversity, but more taxonomists specialized in marine invertebrates are needed.

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.

Two field trips were made during 2017 to Cayo Arenas and Cayo Arcas, southern Gulf of Mexico. Direct and indirect sampling methods focused on shell-less marine heterobranchs were carried out. As a result, 30 species of sea slugs are reported for the first time from these 2 remote reefs off the Yucatán Peninsula. From these, 7 species hold new distribution records for the Gulf of Mexico: Sclerodoris worki, Platydoris angustipes, Polycera odhneri,Hexabranchus morsomus, Limenandra nodosa, Petalifera ramose, and Hermaea cruciata. Hexabranchus morsomus is a considerable west geographical range extension from the known distribution range, so far restricted to the Caribbean Sea. Nine specimens were identified up to genus level: Cuthona sp., Haminoea sp., Petalifera sp. and Elysia sp. With the present contribution, the sea slug richness in the Campeche Bank increases to 94 species.

A new species of the chromodorid genus Felimare (Gastropoda: Heterobranchia) of the Atlantic blue chromatic group is described using material from Cape Verde (eastern Atlantic). Felimare aurantimaculata n. sp. was described based on morphological characters, as well as a molecular phylogeny using two mitochondrial (cytochrome c oxidase subunit I and 16S rRNA) and one nuclear (histone-3) markers. Felimare aurantimaculata n. sp. is characterized by having a ground of dark blue colour with many orange polka dots over the body, dark blue rhinophores and branchial leaves, and very large and not clustered mantle dermal formations (MDFs) at the edge of the mantle, totally absent in the anterior area facing the rhinophores.

The dataset contains information about the “Colección Regional de Moluscos de la Península de Yucatán” (federal register INV-240-01-11) at the Unidad Multidisciplinaria de Docencia e Investigación, Faculty of Science, UNAM. This dataset represents only specimens of Phylum Mollusca identified to genus and species (3969 specimens) from 35 localities of the coast, coral reefs and deep-sea at the Gulf of Mexico and Mexican Caribbean for a period of time from 2007 to 2019. The dataset contains information on the specimens belonging to 166 families, 386 genus, and 542 species. The specimens at the collection have been either identified or validated by professional mollusk taxonomists, providing a significant level of trust in the data. The taxonomists that participated in this process appear in the list of authors.