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