The Biodiversity Catalogue is a product of the FP7 project BioVel (the Biological Virtual e-laboratory) and provides a curated catalogue of Biodiversity Web Services. These services most often work with SOAP as a messaging protocol. Users can do a request and something is returned.
Below some examples of the PESI name service.
Request for a PESI id for the common scoter (Melanitta nigra) using PYTHON
Give species list with id's for the genus scoter (Melanitta)
Why should you use this? In case of working with biological data there is always dispute about the naming of the observed species. PESI is the European name list which has a reference to all species descriptions. If you are looking for a description of species as a metadata within a project you could use this service to give correct descriptions. This is metadata on the level of records, not data sets.
PESI is the back bone of the INSPIRE metadata vocabularies concerning biological data.