The Great Barrier Reef is among the most biodiverse of all marine ecosystems and consequently, much of this diversity remains undocumented. We discovered three new species of parasitic flatworm living in the intestines of Great Barrier Reef fishes. This work highlights the vast number of organisms awaiting discovery in coral reef ecosystems.

Psammodrilidae constitutes a family of understudied, nearly completely ciliated, small-sized annelids, whose systematic position in Annelida remains unsettled and whose internal relationship is here investigated for the first time. Two new species are described, and microscopic size and related morphological traits are reconstructed to have evolved several times within Psammodrilidae. The several cases of miniaturisation with outcomes resembling juveniles of larger relatives indicate that the family is genetically susceptible to progenesis.

Here, we suggest collecting ecological data in a standard way, using a semistructured dataset. This information, fundamental for species identification, can also represent a baseline for species distribution modelling and conservation planning. The description of a hydrozoan species is supplied as a proof of concept for this reference group; the given suggestions could be easily applied to describe other sessile benthic organisms.

A little-known genus of mangrove slugs, Peronina Plate, 1893, is revised here for the first time. It includes two species, one of which is new, which are restricted geographically to the Bay of Bengal and the Malacca Strait. This study describes the morphology, habitats, and genetic diversity of those slugs and contributes to better understand the biodiversity of mangrove invertebrates in South-East Asia.

Our study reports on the occurrence of a species of sponge of the genus Leucetta from the Southern Ocean, Leucetta giribeti, sp. nov. This species was found in shallow waters of Antarctica, where calcareous sponges have not previously been documented. This work describes the species’ morphology and its inter-relationships, and highlights in particular the sperm cells, which have features not previously reported in related species. This work, showing the unique features of this species, is therefore important for our future understanding of this species, and all those related to it.

We undertook phylogenetic and dating analyses of Onychophora using three molecular markers and a strategy to maximize the amount of information for subsets of taxa. We resolve the overall phylogeny of the group, but relationships within the Neotropical taxa remain elusive, and the larger genera are not monophyletic. We provide a biogeographical interpretation that rejects the colonization of Southeast Asia by onychophorans using Europe as a migration route.

The plant bug subfamily Bryocorinae is a diverse group distributed worldwide, comprising pests of crops and species used for the biological control. We provide the taxonomical synopsis of the Bryocorinae tribes, including identification key, distinctive features, natural history notes and distributional patterns. The synthesis will enable users to identify bryocorines to tribal level with confidence and provides a classificatory framework for future revisionary and phylogenetic studies.

The surprising discovery in European waters of a Tritoniid nudibranch that can reach 200 mm in length, has led to the description of a new species belonging to the genus Marionia. The relationships with other closely related species was also investigated, trying to improve the general knowledge about this complex family. This finding represents another demonstration of how much remains to be discovered, even in theoretically well-studied areas.

The restricted distribution of viviparous velvet worms in Tasmania has long been a subject of discussion, but their origin and evolutionary history remain unexplored. In this study we combine morphological, molecular and karyotype methods to revise the two known and to describe two additional viviparous species from this island. Our findings reveal a single origin of all four Tasmanian viviparous species, but the sister group relationship of this clade to either New Zealand of mainland Australian taxa is still uncertain.

Antlions are commonly associated with deserts, although a few are instead denizens of tropical rainforests, where their diversity remains uninvestigated. Here, we focused on one of them, the Neotropical Ripalda, revising it in a cladistic framework. Our study also revealed an American radiation of antlions, rising new, interesting scenarios about the evolution and biogeography of this lacewing family.

Oxynoe is a group of herbivorous sea slugs, some of which feed on highly invasive strains of seaweeds termed ‘killer algae’ due to their rapid spread and toxicity. In this paper, we use molecular and morphological data to resolve taxonomic uncertainties in Oxynoe and describe seven new species. Our findings bring needed stability to the systematics of a traditionally unstable group and informs studies of tropical diversification of specialised marine herbivores.