Unarmoured dinoflagellates with a small hyposome:TorodiniumandLebouridiniumgen. nov. forKatodinium glaucum(Gymnodiniales, Dinophyceae).
We investigated the morphology and evolutionary relationships ofTorodiniumspp. andKatodiniumglaucum, unarmoured dinoflagellates characterized by a small hyposome. An emended generic description ofTorodiniumwas proposed based on light and scanning electron microscopy.Torodiniumexhibited a unique combination of morphological features including a minute hyposome, a long episome with longitudinal ribs and a canal of unknown function on the dextro-lateral side. Unlike any known dinoflagellate both cingulum and sulcus extended in the episome. The apex surface showed ribs that converged in a bill-like projection. The shape of the apical groove was a circular spiral that extended around the apex running in 2.5 turns in an anticlockwise direction. The type speciesT. teredowas usually longer thanT. robustum.The longitudinal outline ofT. teredowas linear, with almost parallel margins, a circular transversal section, a relatively large hyposome and a conspicuous bill-like projection. The longitudinal outline ofT. robustumwas oblong, widened in the middle, with an ellipsoidal transversal section, a small hyposome and a less prominent bill-like projection. Several morphological features ofKatodinium glaucum(=Gyrodinium glaucum) resembledGyrodinium, such as the cingular displacement, longitudinal ribs, trichocysts, rod-shaped and refractile bodies and a capsule that surrounded the spherical nucleus. Distinctive features ofK. glaucumwere the horseshoeshaped apical groove under a tongue-shaped notch pointed towards the dorsal side, and a bifurcated proximal end of the cingulum. Phylogenetic analysis revealed thatTorodiniumspp. andK. glaucumformed two independent lineages with no close relationships with other known dinoflagellates. The morphology ofK. glaucumwas distant from the type species ofKatodinium. We propose the new genus and combinationLebouridinium glaucumgen. nov., comb. nov. for the speciesKatodinium glaucum.
Laboratory of Plankton Systems, Oceanographic Institute, University of São Paulo, São Paulo 05508-900, Brazil.
Fernando
F
Gómez
Hatami 5-20-13, Ondo-cho, Kure, Hiroshima 737-1207, Japan.
Haruyoshi
H
Takayama
Unité d'Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, 91405 Orsay, France.
David
D
Moreira
Unité d'Ecologie, Systématique et Evolution, CNRS UMR 8079, Université Paris-Sud, 91405 Orsay, France.
Purificación
P
López-García
Gymnodinium, Gyrodinium; acrobase; apical groove; athecate Dinoflagellata; molecular phylogeny; naked dinoflagellate; new genus; taxonomy