Re-evaluation of the systematics of two deep-sea species of Thalassometra (Echinodermata: Crinoidea) and its biogeographical implications

Abstract

Biogeography of deep-sea comatulid crinoids is poorly understood owing partly to the lack of detailed taxonomic studies. Recent cruises off Peru dredged up two new, well-preserved specimens of Thalassometra bispinosa, a deep-sea comatulid species which was heretofore only known from the Southern Ocean. These new records enabled re-evaluation of intra-specific variation for both quantitative and qualitative morphological characters. We thus provide a new description of the species, including these new specimens, and discuss the affinities with closely related species. As a consequence, we re-evaluate the systematic position of material previously assigned to T. bispinosa dredged from the Campbell Plateau, Southern Ocean. Discrete morphological characters, measurements and SEM photographs justify reassignment of these specimens to Thalassometra villosa. This species, another poorly known deep-sea comatulid crinoid previously known only from the Aleutian Islands in the North Pacific, is also redescribed. The biogeography of these two deep-sea comatulid species is discussed and hypotheses of their geographical distribution are proposed.

La biogeographie des comatules profondes reste mal connue. Cette lacune est essentiellement due au manque de matériel. Deux campagnes IFREMER récentes, effectuées au large du Pérou, ont permis la récolte de deux spécimens exceptionnellement conservés de Thalassometra bispinosa. Cette espèce de comatule du bathyal profond était connue uniquement de l'Océan Austral. L'étude de la variation morphologique intraspécifique de ces nouveaux spécimens, tant quantitative que qualitative, a permis de donner une description détaillée de l'espèce. Sur la base de cette nouvelle description, nous avons réexaminé la position systématique du matériel provenant du Plateau Campbell (Océan Austral), auparavant attribuée à T. bispinosa. La comparaison des caractères morphologiques externes et des articulations des spécimens concernés a fourni les arguments de l'attribution des spécimens du Plateau Campbell à Thalassometra villosa. En conséquence, nous donnons une nouvelle description de cette seconde espèce bathyale jusqu'alors uniquement connue dans le Pacifique Nord. La biogéographie de ces deux espèces est discutée. Nous proposons un scénario explicatif de leur distribution.

Keywords:

• Echinodermata
• Thalassometra
• comatulid
• deep-sea
• biogeography
• systematics

Acknowledgements

We wish to thank François Bourgois (Paris VI), who led both Nautiperc and Andinaut cruises; Michel Segonzac of the IFREMER who helped retrieve relevant information related to these cruises. Special thanks are due to Cynthia Ahearn and David Pawson (USNM), and Sheila Halsey (NHM) for sending precious material from the ‘Challenger’, ‘Albatross' and ‘Eltanin’ cruises. Mark Norman (Museum Victoria) deserves a special mention for reading the proof of the paper. We thank Michel Roux (Université de Reims), Charles Messing (NOVA University) and Alexander Mironov (Institute of Oceanography, Moscow) for useful comments and discussions. We are also indebted to Olivier Brosseau (MNHN) for helping with SEM techniques, Bruno David (Université de Bourgogne) and Loïc Villier (Université de Rennes) for drawing our attention to the T. bispinosa specimen dredged during the Andinaut cruise.