Animal biodiversity is greatly underestimated in nontemperate marine regions, especially for intertidal benthic organisms such as oysters. Recent surveys in the northern Arabian Gulf suggest the presence of numerous unidentified species, some of which form shallow reef ecosystems while others are cryptic and found under rocks. In this study, we focused on small oysters from Kuwait, which show typical characteristics in common with the genus Ostrea except for the presence of lophine chomata that would link it to the genera Lopha, Dendostrea, and Alectryonella. Phylogenetic analyses based on mitochondrial and nuclear markers unambiguously placed the Kuwait oyster within the Ostreinae as a sister to the Japanese species Ostrea futamiensis. The hypothesis that the Kuwait oyster represents a new species was assessed with phylogenetic and species delimitation methods combined with a morphological assessment. Results corroborated the Kuwait oysters as a new species herein described as Ostrea oleomargarita Oliver, Salvi, and Al-Kandari, sp. nov. The phylogeny of the Ostreinae shows extensive disagreement between morphology-based genera and phylogenetic clades. The genus Ostrea is polyphyletic, and the form and distribution of taxonomic characters such as chomata are not as definitive as suggested in previous studies. This study, along with other recent investigations, confirmed the Arabian Gulf as a key region for discovering marine animal diversity and suggested a possible biogeographic divide between the Eastern and Western Indo-Pacific. A pattern that has been documented in a growing number of taxa and that warrants further research attention.

The accuracy of the DNA barcoding tool depends on the existence of a comprehensive archived library of sequences reliably determined at species level by expert taxonomists. However, misidentifications are not infrequent, especially following large-scale DNA barcoding campaigns on diverse and taxonomically complex groups. In this study we used the species-rich flea beetle genus Longitarsus, that requires a high level of expertise for morphological species identification, as a case study to assess the accuracy of the DNA barcoding tool following several optimization procedures. We built a cox1 reference database of 1502 sequences representing 78 Longitarsus species, among which 117 sequences (32 species) were newly generated using a non-invasive DNA extraction method that allows keeping reference voucher specimens. Within this dataset we identified 69 taxonomic inconsistencies using barcoding gap analysis and tree topology methods. Threshold optimisation and a posteriori taxonomic revision based on newly generated reference sequences and metadata allowed resolving 44 sequences with ambiguous and incorrect identification and provided a significant improvement of the DNA barcoding accuracy and identification efficacy. Unresolved taxonomic uncertainties, due to overlapping intra- and inter-specific levels of divergences, mainly regards the Longitarsus pratensis species complex and polyphyletic groups L. melanocephalus, L. nigrofasciatus and L. erro. Such type of errors indicates either poorly established taxonomy or any biological processes that make mtDNA groups poorly predictive of species boundaries (e.g. recent speciation or interspecific hybridisation), thus providing directions for further integrative taxonomic and evolutionary studies. Overall, this study underlines the importance of reference vouchers and high-quality metadata associated to sequences in reference databases and corroborates, once again, the key role of taxonomists in any step of the DNA barcoding pipeline in order to generate and maintain a correct and functional reference library.

Since the opening of the Suez Canal in 1869, hundreds of Indo-Pacific species have rapidly colonised the Mediterranean. Understanding the spatial and temporal patterns of this biological invasion is crucial for assessing its ecological impact. A notable example is the non-indigenous oyster Dendostrea sp., first discovered in Türkiye in 1998 and later found throughout the easternmost Mediterranean, though its identity remained uncertain. This study clarifies the taxonomic identity and the introduction pathways of Dendostrea sp. using molecular analyses. Over 100 specimens from 25 sites in the eastern Mediterranean, as well as Île d’Ambre and Rodrigues in the Mauritius Archipelago (the native range), were sequenced for mitochondrial DNA (COI) and compared to 422 sequences from GenBank. Phylogenetic and species delimitation analyses identified the Mediterranean oysters as D. cf. crenulifera, conspecific with oysters from Rodrigues. The Mediterranean populations exhibited high genetic diversity, lack of phylogeographic structure and showed no evidence of a founder effect. These findings suggest that D. cf. crenulifera entered the Mediterranean over two decades ago through multiple shipping-mediated introductions from its native range and successfully established, likely aided by the decline of native biodiversity. The observed genetic diversity pattern across the Mediterranean indicates high propagule pressure driving the species’ invasion history, which likely underpins its establishment success by reducing the deleterious consequences of population bottlenecks and overcoming the so-called genetic paradox. This study underscores the value of molecular surveys in identifying taxonomically challenging non-indigenous species and uncovering their invasion histories.

The common practice of using subspecies as conservation targets raises the question of whether efforts are focused on preserving conspicuous components of the species’ phenotypic variability rather than evolutionarily significant units. To address this question, in this study we performed a comprehensive morphological and genetic assessment on all the subspecies of wall lizard described for the Aeolian Archipelago (Italy) to determine whether they represent distinct evolutionary lineages and/or discrete phenotypic partitions. Further, we applied a monophyly test to 70 subspecies belonging to seven wall lizard species occurring in Italy, based on our results and on previous phylogeographic studies. We found that none of the Aeolian subspecies represents a distinct evolutionary lineage, despite some morphological differentiation of island populations across the archipelago, suggesting a very recent origin of island populations and of the observed phenotype variation. Across seven wall lizard species, tests revealed that lizard subspecies rarely (< 9% of cases) match evolutionary units. This study demonstrates that intraspecific taxonomy of wall lizards is a poor predictor of phylogeographic partitions and evolutionary units, and therefore of limited use (if not dangerous) for defining conservation and management units. A better approach would be relying on the integration of genomic and phenotypic data to assess the evolutionary significance and conservation value of phenotypic and genetic units within species.