Macrodactyla aspera (Haddon and Shackleton, 1893)

Yap, Nicholas Wei Liang, Mitchell, Michela Lee, Quek, Zheng Bin Randolph, Tan, Ria, Tan, Koh Siang & Huang, Danwei, 2023, Tripedalia maipoensis Sun & Tsui & Wong & Cheung & Ng & Or & Qiu 2023, sp. nov., Zoological Studies 62 (29), pp. 1-25 : 21

Macrodactyla aspera as a potential threat to public safety

In bearing visible nematocyst batteries, and having large nematocysts in its tentacles (i.e., undischarged capsules of length> 50 µm), M. aspera may be capable of delivering a painful sting on contact. Dolfeinia armata is another, similar example: it bears visible nematocyst batteries on its tentacles, and have basitrichs that are> 50 µm (e.g., up to 76 µm; see Carlgren 1945). Other sea anemones that have been reported to be a threat to public health, such as Phyllodiscus semoni and members of Actinodendridae also bear specialised structures along their tentacles that harbour a dense reservoir of nematocysts (e.g., nematocyst batteries) and cnidae larger in size (for sizes, see Carlgren 1945; Fautin et al. 2009; Hoeksema and Crowther 2011). Following this line of logic, we suggest that sea anemone species that may inflict painful stings are ones that usually bear specialised structures on their tentacles, and/or have large nematocysts; M. aspera may also be a potential threat to humans. This requires further investigation and comparisons with other species that are not deemed to be a threat but also bear large nematocysts and specialised structures on their tentacles (e.g., Haloclava hercules Izumi, 2021 ).

Importance of re-examining name-bearing type specimens

In this study, we re-described M. aspera using new morphological data (i.e., living appearance, cnidom) gathered not only from fresh and voucher specimens, but also from the name-bearing specimen of M. aspera [= C. aspera ]. This was necessary to ascertain that established diagnostic characters reported for Macrodactyla (e.g., Stephenson 1921 1922; Carlgren 1949; Dunn 1981) were truly definitive of the genus. Here, we found that the complete mesentery numbers and arrangement present in the lectotype differ from previous accounts that were published. Our findings were not unexpected; long-accepted diagnostic characters of a taxon are often disputed when new observations arise from a careful reexamination of name-bearing types. Thorough treatment involving a comprehensive study of name-bearing types will be needed to resolve the taxonomic challenges for many groups of sea anemones. Members of the superfamily Actinioidea are taxonomically unresolved ( Rodríguez et al. 2014; Titus et al. 2019) and will benefit from this detailed approach. Recent efforts have demonstrated such an approach is feasible and fruitful (e.g., Fautin and Tan 2016; Yap et al. 2019 2021).