Review of the genus Zygothuria Perrier, 1898 and the Atlantic group of species of the genus Mesothuria Ludwig, 1894 (Synallactidae: Holothuroidea) with description of the new species Mesothuria milleri sp. nov.

Abstract

Species of the genus Mesothuria (fam. Synallactidae) occurring in the Atlantic Ocean are revised. The genus includes 25 valid species, nine of them known from the Atlantic. The new species Mesothuria milleri sp. nov. is described from the north-east Atlantic. It is argued that the genus Zygothuria, established by Perrier in 1898 and recognized later only by Deichmann, should be maintained as a separate genus. Mesothuria and Zygothuria differ in body form, arrangement of ambulacral appendages, and structure of segments of calcareous ring and ossicles from the body wall. The six known species of Zygothuria are reviewed. Zygothuria oxysclera, a former variation of Zygothuria lactea, is proposed as a valid species. Identification keys to species of the genus Zygothuria and Atlantic species of the genus Mesothuria are provided. Data on the life history and reproductive biology of Mesothuria milleri and Zygothuria lactea are given. Both species are common in the north-east Atlantic.

Keywords:

• Mesothuria
• Zygothuria
• taxonomy
• new species
• distribution
• reproduction

Acknowledgements

The authors thank the following curators of zoological collections and museum staff for professional assistance with material and for guidance: David Pawson and Cynthia Ahearn (United States National Museum, Smithsonian Institution), Claus Nielsen and Margit Jensen (Zoological Museum, University of Copenhagen), Alfredo Laguarda-Figueras (Colección Nacional de Equinodermos UNAM), Andrew Cabrinovich (Natural History Museum, London), Nadia Ameziane (Museum National d'Histoire Naturelle), Guðmundur Guðmundsson, Guðmundur Helgason and Olafur Asthorsson (Sandgerdi Biological Station, BIOICE collection), Jon Kongsrud and Endre Willassen (Museum of Zoology, University of Bergen) and Craig Young (formerly Harbor Branch Oceanographic Institute). The authors are also grateful to the late John Gage (SAMS) for his advice and valuable ship time. Mark O'Loughlin and one anonymous reviewer helped us to improve the manuscript. Travels to museums in part were funded by the Royal Society (London) (for AVG) and MAR-ECO (project of the Census of Marine Life program) (for AVG and AVR). This paper is a contribution to the UK Natural Environment Research Council's ‘Oceans 2025’ project and to the EU project HERMIONE (Hotspot Ecosystem Research and Man's Impact on European Seas).