The Splanchnotrophidae is a family of highly modified endoparasitic copepods known to infest nudibranch or sacoglossan sea slug hosts. Most splanchnotrophid species appear to be specific to a single host, but some were reported from up to nine different host species. However, splanchnotrophid taxonomy thus far is based on external morphology, and taxonomic descriptions are, mostly, old and lack detail. They are usually based on few specimens, with intraspecific variability rarely reported. The present study used molecular data for the first time to test (1) the current taxonomic hypotheses, (2) the apparently strict host specificity of the genus Ismaila and (3) the low host specificity of the genus Splanchnotrophus with regard to the potential presence of cryptic species. Phylogenetic analyses herein used sequences of the barcoding region of the cytochrome oxidase I (COI) gene from 40 specimens representing 13 species of five genera. Species delimitation approaches include distance and barcoding gap analyses, haplotype networks and diagnostic nucleotides. Molecular results are largely compatible with the commonly accepted, morphology-based taxonomy of the Splanchnotrophidae. Strict host specificity could be confirmed for two Ismaila species. COI analyses also supported the idea that Splanchnotrophus angulatus is host-promiscuous. In Ismaila, morphology seems more suitable than barcoding to display speciation events via host switches in a recent Chilean radiation. In Splanchnotrophus, some genetic structure suggests ongoing diversification, which should be investigated further given the inadequate morphology-based taxonomy. The present study thus supports the presence of two different life history strategies in splanchnotrophids, which should be explored integratively.

The Bahamian archipelago is one of the richest regions in the Caribbean province and its importance as a hot spot of biodiversity and potential centre of origination of new species in the tropical western Atlantic has been suggested. In this paper I report on the sea slugs collected during a field trip to Eleuthera Island, the Bahamas. Animals were collected from the intertidal down to five metres deep by direct sampling. Nineteen species of opisthobranchs were found including two new records to the Bahamas (Berghia stephanieae and Gastropteron vespertilium) and three putatively new species of Haminoea. Colour variation was detected on adults of the species Chelidonura hirundinina and Bulla occidentalis, the latter suggesting isolation across a reduced geographical scale. Ontogenetic variation in Philinopsis cf. pusa was found and is here documented. The uniqueness of the Bahamian biodiversity is highlighted.

The Brazilian Northeastern coast includes diverse ecosystems, particularly mangroves, coral and sandstone reefs. Although apparently high, the biodiversity of marine invertebrates from the State of Alagoas is still poorly documented. This study presents 28 new records of opisthobranch molluscs from Alagoas, 11 of which are also new records from the Brazilian Northeastern coast. In addition to comprising an important addition to knowledge about Alagoas reef biodiversity, the new records are useful data for future investigations such as biogeographical studies. Therefore, a list of all opisthobranch species known to date from Alagoas, as well as colour photographs of 32 species is provided.