Unexpected systematic affinities and geographic expansion of a marine alien hydroid (Cnidaria: Hydrozoa)

Abstract

Biological systematics provides taxonomic information and expertise for biogeography and biological invasion research and management. However, the systematic classification of most taxa, including some alien and invasive species, relies only on morphology. This applies for example to Sertularella tongensis Stechow, 1919 (Cnidaria: Sertulariidae), an alien hydrozoan recently reported in the Mediterranean. Its genus affiliation is still unclear and controversial. Historically, it has been assigned to several existing genera. However, molecular data (COI, 16S, 18S, 28S) provided here do not support these previous assignments. Instead, integrative analyses combining morphological and molecular data support reassigning this species to a new genus, Bicaularia gen. nov. A biogeographic review revealed that this species is widely distributed in the mid- and low-latitude waters of the Indo-Pacific region, and is spreading to some tropical and temperate regions including the Mediterranean and Caribbean Seas, as well as Korea and Japan. This expansion may be attributable to human activity such as shipping through the Suez and the Panama Canals. However, the new record attached to a floating Sargassum algal fragment in the surface water of the open Pacific, might suggest a neglected cryptic spread pathway with the assistance of floating biological organisms. Our findings shed light on the complexity of the phylogeny and spread pathway of the investigated hydrozoan species. We regard the fine systematics as the first step towards future global sampling for molecular studies aiming to elucidate the origins and pathways for alien and invasive species.

http://zoobank.org/urn:lsid:zoobank.org: pub: 45AB0849-1E3B-477FB643-1B3B4603C1FF

Key words:

• Alien and invasive species
• floating macro-algae
• global spread
• molecular phylogeny
• fine systematics

Acknowledgements

We thank Dr Jeanette Watson (Museum of Victoria, Australia) for revisions on the contents and language, Dr Horia Galea (Hydrozoan Research Laboratory, France) for samples and discussions.

Author contributions

XS examined the XMU and MBM material, prepared the manuscript drafts; ML and XS conducted molecular analyses; XS and CG prepared the systematics section, reviewed the Mediterranean alien hydrozoan records; BR examined the ZSM material, prepared the diagrammatic drawings, revised the language; all authors wrote the paper.

Disclosure statement

The authors declare that they have no conflict of interest.

Supplemental data

Supplemental data can be accessed here: https://dx.doi.org/10.1080/14772000.2019.1583690.

Associate Editor: Andrea Waeschenbach

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (41876180), the China Postdoctoral Science Foundation (2018T110647, 2018M632579), and the Outstanding Postdoctoral Scholarship from the State Key Laboratory of Marine Environmental Science at XMU (MEL). This is the authors' scientific research report QT05.