Dispersal ability, habitat characteristics, and sea-surface circulation shape population structure of Cingula trifasciata (Gastropoda: Rissoidae) in the remote Azores Archipelago

How we study cryptic species and their biological implications: A case study from marine shelled gastropods

Methodological and biological considerations are intertwined when studying cryptic species. A potentially large component of modern biodiversity, the frequency of cryptic species among taxonomic groups is not well documented. The term "cryptic species" is imprecisely used in scientific literature, causing ambiguity when interpreting their evolutionary and ecological significance. This study reviews how cryptic species have been defined, discussing implications for taxonomy and biology, and explores these implications with a case study based on recently published literature on extant shelled marine gastropods. Reviewed gastropods were recorded by species. Records of cryptic gastropods were presented by authors with variable levels of confidence but were difficult to disentangle from inherent biases in the study effort. These complexities notwithstanding, most gastropod species discussed were not cryptic. To the degree that this review's sample represents extinct taxa, the results suggest that a high proportion of shelled marine gastropod species are identifiable for study in the fossil record. Much additional work is needed to provide a more adequate understanding of the relative frequency of cryptic species in shelled marine gastropods, which should start with more explicit definitions and targeted case studies.

Evaluating the taxonomic status of the large sized Tricolia Risso, 1826 in the Northeast Atlantic and Mediterranean Sea

Despite a long history of taxonomic studies on the genus Tricolia Risso, 1826, there is a shortfall on thorough systematic molecular reviews of the taxon from the NE Atlantic and Mediterranean coasts. Aiming to assess the genetic distinctness among morphospecies and the taxonomic status of currently accepted large sized species in these areas, we conducted a molecular phylogenetic analysis of the genus based on one mitochondrial (cox1) and two nuclear (28S and ITS2) markers. Seven Tricolia species were consistently retrieved in the analyses, including a new genetic lineage in the NE Atlantic designated as Tricolia sp. 1. Molecular analyses revealed that only one species, T. azorica, occurs in the NE Atlantic archipelagos. The sister taxa T. pullus (Mediterranean) and T. picta (NE Atlantic) should be classified as distinct species, instead of subspecies of the T. pullus group (sensu Gofas 1982). Tricolia miniata is also a complex of species in the Mediterranean and future studies across the distribution range are necessary to clarify its status.

Morphospecies and molecular diversity of ‘lace corals’: the genus Reteporella (Bryozoa: Cheilostomatida) in the central North Atlantic Azores Archipelago

Background

As in most bryozoans, taxonomy and systematics of species in the genus Reteporella Busk, 1884 (family Phidoloporidae) has hitherto almost exclusively been based on morphological characters. From the central North Atlantic Azores Archipelago, nine Reteporella species have historically been reported, none of which have as yet been revised. Aiming to characterise the diversity and biogeographic distribution of Azorean Reteporella species, phylogenetic reconstructions were conducted on a dataset of 103 Azorean Reteporella specimens, based on the markers cytochrome C oxidase subunit 1, small and large ribosomal RNA subunits. Morphological identification was based on scanning electron microscopy and complemented the molecular inferences.

Results

Our results reveal two genetically distinct Azorean Reteporella clades, paraphyletic to eastern Atlantic and Mediterranean taxa. Moreover, an overall concordance between morphological and molecular species can be shown, and the actual bryozoan diversity in the Azores is greater than previously acknowledged as the dataset comprises three historically reported species and four putative new taxa, all of which are likely to be endemic. The inclusion of Mediterranean Reteporella specimens also revealed new species in the Adriatic and Ligurian Sea, whilst the inclusion of additional phidoloporid taxa hints at the non-monophyly of the genus Reteporella.

Conclusion

Being the first detailed genetic study on the genus Reteporella, the high divergence levels inferred within the genus Reteporella and family Phidoloporidae calls for the need of further revision. Nevertheless, the overall concordance between morphospecies and COI data suggest the potential adequacy of a 3% cut-off to distinguish Reteporella species. The discovery of new species in the remote Azores Archipelago as well as in the well-studied Mediterranean Sea indicates a general underestimation of bryozoan diversity. This study constitutes yet another example of the importance of integrative taxonomical approaches on understudied taxa, contributing to cataloguing genetic and morphological diversity.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12862-022-02080-z.