title: Balechina and the new genus Cucumeridinium gen. nov. (Dinophyceae), unarmored dinoflagellates with thick cell coverings.
abstract: The genus Balechina (=subgenus Pachydinium) was established for heterotrophic gymnodinioid dinoflagellates with a thick cell covering. The type species, B. pachydermata (=Gymnodinium pachyderm-atum), showed numerous fine longitudinal striae, whereas B. coerulea (=G. coeruleum) showed ~24 prominent longitudinal surface ridges or furrows and a distinctive blue pigmentation. We have investigated the morphology and molecular phylogeny of these taxa and the species Gymnodinium cucumis, G. lira and G. amphora from the western Mediterranean, Brazil and Japan. Sudden contractions at the cingulum level were seen in B. pachydermata, which also showed a high morphological variability which included morphotypes that have been described as Amphidinium vasculum, G. amphora, G. dogielii and G. gracile sensu Kofoid and Swezy. Molecular phylogeny based on small subunit rRNA gene sequences revealed that Balechina coerulea, G. cucumis and G. lira formed a clade distantly related to the clade of the type species, B. pachydermata, and G. amphora. We propose the new genus Cucumeridinium for the species with longitudinal ridges and a circular apical groove (Cucumeridinium coeruleum comb. nov., C. lira comb. nov. and C. cucumis comb. nov.), and Gymnodinium canus and G. costatum are considered synonyms of C. coeruleum. The genus Balechina remains for the species with a double-layer cell covering, bossed surface with fine striae, and an elongated elliptical apical groove. At present, the genus is monotypic containing only B. pachydermata.
authors.affiliation: Laboratory of Plankton Systems, Oceanographic Institute, University of São Paulo, Praça do Oceanográfico 191, Cidade Universitária, Butantã, São Paulo, 05508-900, Brazil.
authors.forename: Fernando
authors.initials: F
authors.lastname: Gómez
authors.affiliation: Unité d'Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, Bâtiment 360, Orsay Cedex, 91405, France.
authors.forename: Purificación
authors.initials: P
authors.lastname: López-García
authors.affiliation: Hatami 5-20-13, Ondo-cho, Kure, Hiroshima, 737-1207, Japan.
authors.forename: Haruyoshi
authors.initials: H
authors.lastname: Takayama
authors.affiliation: Unité d'Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, Bâtiment 360, Orsay Cedex, 91405, France.
authors.forename: David
authors.initials: D
authors.lastname: Moreira
keywords: Gymnodinium; Mediterranean Sea; North Pacific Ocean; South Atlantic Ocean; athecate Dinoflagellata; autotomy; blue pigmentation; intraspecific variability; molecular phylogeny; new genus