Assessing the taxonomy of Heterometra-like feather stars (Echinodermata: Crinoidea: Himerometroidea) based on morphology and molecular data

Abstract

The taxonomic classification of feather stars (Echinodermata: Crinoidea) has been unstable due to the extensive use of environmentally and ontogenetically variable morphological characters for diagnosing taxa. Furthermore, crinoids remain poorly studied even in some of the most biodiverse regions of the world, such as Southeast Asia. Historically, Heterometra (Comatulida: Himerometroidea: Himerometridae) has been the most abundant and speciose genus reported in Singapore, but species-level identification is challenging due to the lack of clear diagnostic features. In this study, the identities of 48 Heterometra-like crinoids collected from 21–64 m in southern Singapore were assessed based on detailed morphological examination and molecular phylogenetic inference. Specimens were initially grouped into three morphospecies, and phylogenetic analyses based on the cytochrome c oxidase subunit I gene placed these morphospecies in three distinct clades separated by large interspecific distances. Phylogenetic results coupled with additional examination of morphology confirmed the three morphotypes as Heterometra crenulata, Zygometra cf. comata, and H. schlegelii. The phylogeny further corroborates recent work showing that Heterometra is polyphyletic, with all examined species other than H. crenulata nested within the family Mariametridae, while Zygometra is nested in family Himerometridae. The separation of crenulata from other Heterometra and comparison of new material with type specimens lead us to treat this taxon as Homalometra crenulata comb. nov. and Ho. denticulata as its junior synonym. These findings highlight the need for a thorough revision of Himerometroidea.

Keywords:

• biodiversity
• Central Indo-Pacific
• COI
• phylogenetics
• pinnular morphology
• seafloor
• Southeast Asia

Acknowledgements

We are grateful to the team at the Tropical Marine Science Institute (TMSI), National University of Singapore, that assisted with sample collection; Rene Ong for providing images; Iffah Iesa for assistance with specimens at the Lee Kong Chian Natural History Museum; Sudhanshi Jain for helping with molecular sequencing; and the St John’s Island National Marine Laboratory for facilities support. Specimens examined in the study were collected under the project ‘Preliminary wave energy resource assessment of Singapore and Southeast Asia: Biological communities of St John’s Island’ carried out by TMSI on behalf of the Energy Research Institute, Nanyang Technological University. The study also benefited from comparative material collected during the Comprehensive Marine Biodiversity Survey (2010–2015) co-led by the National Parks Board and National University of Singapore. We wish to thank Holly Morgenroth, FLS, Collections Officer, Royal Albert Memorial Museum & Art Gallery, Exeter, UK, for the images in Fig. 21. Two reviewers provided constructive comments and suggestions that improved the manuscript.

Author contributions

Foo, S.H.: Re-examination of specimens, sequencing, data analysis, writing and editing of manuscript. Taylor, K.H. & Rouse, G.W.: Provided additional sequences for phylogenetic reconstruction, reviewed manuscript, intellectual input on taxonomic decisions. Messing, C.G.: Provided content on morphology, history of taxonomy and nomenclature, images of type and ME specimens of Ho. crenulata, and editing of manuscript. Tay, T.S.: Collection and preliminary examination of specimens, mentored first author on morphological examination. Tan, K.S.: Provided supervision, facility, and material access to the first author. Huang, D.: Supervised the project, data analysis, writing and editing of manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

 

Associate Editor: Andrea Waeschenbach

Additional information

Funding

This work was supported by the National Research Foundation, Prime Minister’s Office, Singapore under its Marine Science R&D Programme (MSRDP-P03); and EXPLORE Young Marine Scientist Research Award to SHF.