Elphidium williamsoni Haynes, 1973 is a foraminiferal species that has been used extensively in relative sea level and climate change studies, as it is characteristic of intertidal zones. Identifying this and other species of Elphidium has proven difficult because key morphological characteristics show a wide range of variation causing widespread confusion in determinations.
A study led by University of St Andrews PhD student Angela Roberts and recently published in the Journal PloSOne, has gone a long way to clearly define this important foraminiferal species. The study is based on measurements from Museum type specimens as well as genetic studies on contemporary material collected from the same location as the type specimens.
Rigorous taxonomy is important because errors in identification introduce errors in palaeoenvironmental reconstructions. Most studies rely on comparative study of modern and fossil species so our understanding of the ecology and biogeographical distributions of modern species is vital to help us outline changes in biodiversity through time, some of which can be climate driven.
Confusion over Elphidium williamsoni is not a new issue. Williamson (1858) had incorrectly identified the species as Polystomella umbilicatula, originally described by Walker and Jacob way back in 1798. Haynes (1973), in his revision and having reference to Williamson’s original material in the Museum, described Elphidium williamsoni as new, his holotype and paratypes coming from living specimens from the Clettwr transect in the Dovey Estuary, Wales.
E. williamsoni has similarities with other elphidiid species, and has at times been confused with Elphidium excavatum or considered a subspecies of the E. excavatum complex; E. excavatum williamsoni.
Molecular analysis of modern benthic foraminifera suggests limitations of classification based solely on morphological features; an estimated 10-25% of modern benthic foraminiferal names may represent species already described. Conversely, some studies have identified a number of cryptic species in material that, based on morphology alone, seemingly belonged to the same species. Traditional taxonomists using morphological features to classify species have been reticent of these studies, claiming that the identifications of the material analysed is not anchored in taxonomic concepts based on type specimens.
The study by Roberts et al. is novel as it combines analysis of the small subunit ribosomal RNA gene of live specimens from the type locality with analysis of 16 quantitative morphometric variables on Museum type specimens to fully characterise the benthic foraminiferal species concept of Elphidium williamsoni Haynes, 1973.
The results support Haynes’ original type description and diagnosis and attest to his taxonomic skill in choosing type material to represent morphological variability within a single species. It also suggests E. williamsoni should not be considered a subspecies of the E. excavatum complex.
Many of these key diagnostic features recognised by Haynes are significant in determining interspecific relationships between the E. williamsoni type specimens and other genetically distinct Elphidium species. They also show that some important morphological features recognised by Haynes, such tubercles, shell roundness and total number of chambers, are not useful to distinguish E. williamsoni from other elphidiids.
Roberts et al. also suggest that future confusion can be avoided if molecular studies publish SEM or light microscope images as part of their analyses. Many suitable on-line databases are available showing images of Foraminifera. They emphasise that these online databases should complement and not replace the curation, illustration and study of original type material.
John Haynes’ research collection as well as a wide range of other type specimens with complementary materials such as original samples and residues are available for study at the Museum on request. We welcome the finding of Roberts et al. and encourage all those working on projects like this to make use of our collections.