Rogacheva A.V., Mironov A.N., Minin K.V., Gebruk A.V. 2013. Morphological evidence of depth-related speciation in deep-sea Arctic echinoderms // Invertebrate Zoology. Vol.10. No.1: 143–166 [in English].

P.P. Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovsky Pr., 36, Moscow, 117997, Russia, e-mail:

KEY WORDS: morphological variability, Arctic Echinodermata, deep-sea fauna, evolution, adaptations.

ABSTRACT: Three eurybathic cosmopolitan genera of echinoderms, the holothurians Elpidia, the stalked crinoids Bathycrinus and the echinoids Pourtalesia, are widely distributed in the deep Arctic Ocean. The genera Echinus and Gracilechinus occur in the Arctic only in the near-Atlantic sector of the basin. In all the five genera, there is a pronounced difference in morphology between specimens occurring at different depths. It is suggested that these differences reflect the depth-related speciation that took place following three scenarios. The genera Elpidia, Bathycrinus and Pourtalesia penetrated the Arctic Ocean at bathyal depths and subsequently dispersed down into abyssal and upwards into upper bathyal and sublittoral. The vertical dispersion of the genera Echinus and Gracilechinus went along one direction: from the sublittoral (0–200 m) to the abyssal (>2000 m). In the genus Elpidia (the first scenario), new species appeared as a result of colonisation both upward and down from the bathyal. In the genera Bathycrinus and Pourtalesia (the second scenario) the radiation occurred as a result of colonization only down from the bathyal to the abyssal. In the genus Echinus and Gracilechinus (the third scenario), new species appeared along the colonization down, though not from the bathyal but from the sublittoral. Juvenile characters of shallow-water species of Echinus and Gracilechinus retain in adult deep-sea specimens. Morphological peculiarities of abyssal Bathycrinus and Pourtalesia can be related to trophic adaptations or decreasing of predators pressure in the abyssal.

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