Zhadan A.E.1, Tsetlin A.B.2 2009. Polychaetes from deep pelagic zone of the Mid-Atlantic ridge // Invertebrate Zoology. Vol.5 (for 2008). No.2: 97–109 [in English].

1 White Sea Biological Station, Biological Faculty, Moscow State University, Moscow 119992, Russia. E-mail: azhadan@wsbs-msu.ru (corresponding author)

2 Department of Invertebrate Zoology, Biological Faculty, Moscow State University, Moscow 119992, Russia. E-mail: atzetlin@wsbs-msu.ru

KEY WORDS: bathypelagic zone, Mid-Atlantic ridge, Polychaeta, Yndolacia, Hesionidae, Amphinomidae, Buskiella abyssorum.

ABSTRACT: Polychaetes from bathypelagic zone of the Mid-Atlantic ridge were studied using light and scanning electron microscopy. Descriptions of Yndolacia sp. (Yndolaciidae), Hesionidae gen.sp. larvae, Amphinomidae gen. sp. and Buskiella abyssorum (Flotidae) are given. Yndolacia sp. differs from previously described specimens (Støp-Bowitz, 1987; Buzhinskaja, 2004) by combination of characters such as simple (not ramified) nuchal organ, separated first and second segments, number of segments and chaetae, and relative length of tentacular cirri. Yndolacia sp. has an unusual type of axial proboscis with dorsal part much longer than ventral, with ciliar bundles and glands openings on the inner surface. Phylogenetic position of Yndolaciidae is discussed. Hesionidae gen.sp. larvae show a combination of well developed body with the segments number close to that of adults, larval prostomium with very early appendage rudiments, and well-developed prototroch. This morphology can be considered as an adaptation for prolonged swimming of a relatively large animal. Amphinomidae g. sp. These normally benthic animals were caught in the water column in spite of their adult morphology. They are most similar to Notopygos, but differ by absence of forked chaetae.

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