Taxonomy and Molecular Phylogeny of the Sea Anemone Macrodactyla (Haddon, 1898) (Cnidaria, Actiniaria), with a Description of a New Species from Singapore

Abstract

Sea anemones (Cnidaria, Actiniaria) are a successful group of marine invertebrates found in a diverse range of environments globally. In spite of their ubiquity, identities for many sea anemones remain unverified, especially those from the Indo-West Pacific region. Here, we clarify the taxonomy of the poorly known Macrodactyla aspera, a shallow-water species first described from the Torres Straits in northern Australia. We re-describe M. aspera based on new morphological and molecular data gathered from the type specimen, other museum vouchers, and from fresh material collected from Singapore. We tested the monophyly of Macrodactyla using three mitochondrial (12S, 16S and cox3) and one nuclear (28S) marker based on three congeners, recovering this genus to be polyphyletic. As a consequence, we transferred M. doreensis to the genus Heteractis, and describe a new species, Macrodactyla fautinae sp. nov. While both M. aspera and M. fautinae sp. nov. share the same arrangement and number of complete mesenteries, a similar distribution of cnidae, and are not symbiotically associated with any other biota, M. fautinae sp. nov. has perforated, lobe-like verrucae on its column, and lacks nematocyst batteries on its tentacles, unlike M. aspera. These two species also occur in similar habitats in Singapore. Finally, because M. aspera strongly resembles Dofleinia armata, the latter species flagged as a danger to public health due to its ability to inflict painful stings, we tested the relationship between these species and found them not to be closely related. However, tentacles of M. aspera, like D. armata, are densely covered with nematocyst batteries and harbour large nematocysts; we infer that M. aspera may also be capable of delivering stings that endanger public health. This study builds upon a growing number of studies that aim to ascertain identities and systematics of sea anemones historically reported from the Indo-West Pacific. Our findings will facilitate accurate species identification, which is crucial for advancing research, formulating conservation measures, and protecting public health.