Anatomy of a hermit crab

A new study led by the Spanish Institute of Oceanography (IEO-CSIC) and in collaboration with the University of Malaga and the Institute of Marine Sciences of Andalusia (ICMAN-CSIC) has conducted the most comprehensive review to date of hermit crabs (superfamily Paguroidea) found on the Iberian Peninsula and in Macaronesia (the Azores, the Canary Islands, and Madeira).

The study, published in the journal Marine Ecology, documents 55 different species, representing a significant increase compared to previous lists, and generates a molecular database for 35 of these species for the first time.

Hermit crabs are decapod crustaceans characterized by using empty shells—usually snail shells—to protect their abdomens. Unlike other crabs, their bodies are not completely covered by a rigid shell, forcing them to seek refuge in external structures that must be periodically replaced as they grow.

The study has updated the list of known species of these animals by combining genetic data (DNA information) with morphological observations (physical appearance and external characteristics).

"This work has significantly expanded our understanding of hermit crab biodiversity," says Bruno Almón, first author of the study and a researcher at the IEO's Vigo Oceanographic Center. "This type of research is essential for conservation, because if we don't know what species exist, we won't be able to protect them," Almón points out.

This work, beyond focusing on the diversity of hermit crabs, also underscores the importance of combining traditional methods, such as direct observation, with modern molecular tools based on genetic analysis. This improves the accuracy with which species are identified and opens up new avenues for investigating the evolution of marine crustaceans and their role in ecological balance.

As sea temperatures rise due to climate change, many tropical species are beginning to move northward. "If we know the local fauna well, we can more easily recognize when a "new" species is arriving in a place where it didn't previously live. These movements help scientists predict how marine ecosystems will evolve in the future," explains José A. Cuesta, a researcher at ICMAN.

The data for this study come from Bruno Almón's doctoral thesis and compile information obtained over years of work by the team, including sampling in coastal areas, fishing campaigns, and historical museum collections.

"There's still much to discover. There are little-explored marine regions and deep-sea habitats where little research has been done, and it's very likely that more unknown species live there," Almón concludes.