Oxyrrhis F.Dujardin, 1841
Holotype species: Oxyrrhis marina Dujardin
Original publication and holotype designation: Dujardin, F. (1841). Histoire naturelle des Zoophytes, Infusoires, comprenant la physiologie et la clasification de ces animaux et la manière de les étudier à l'aide du microscope. pp. i-xii, 1-684. Paris: Librarie Encyclopédique de Roret.
Description: Small (10-45 µm long) sub-ovoid, heterodynamic, biflagellate cells, unicellular but sometimes in pairs of two. The cell has a large asymmetric postero-ventral depression. Here a tentacle-like lobe originates, directed posteriorly. Cingulum and sulcus are missing. Cell wall smooth, thin without thecal cellulosic plates but with scales. Scales also present on the flagella. The subpellicular microtubular cytoskeleton differs from that of other dinoflagellates as all microtubules are oriented longitudinally and do not attach or abut transverse microtubular arrays. They occur in groups of three or four on the dorsal side but singly on the ventral side. The flagellar apparatus is asymmetric and extremely complex, consisting of a longitudinal and a transverse basal body that gives rise to eight structurally different compartments. Both flagella share the same cylindrical morphology and size. The posteriorly oriented longitudinal flagellum propagates helicoidal waves that push the cell forward whereas the transverse flagellum exhibits a beat pattern superimposed on a permanent corkscrew folding. Their beat frequencies are about 50 -60 Hz. The transverse flagellum contains a small fibre, 20 nm in diam., associated with doublet no. 7, whereas the longitudinal flagellum is sustained by a large (200-300 nm) hollow structure closely resembling the paraflagellar rod described for euglenids and kinetoplastids. The nucleus is of the dinokaryotic type with about 40 permanently condensed chromosomes but have much more histones than that of other dinoflagellates. During mitosis, dense plaques develop in the nuclear envelope at prophase and give rise to an intracellular spindle. Some of the microtubules associate with the chromosomes while others extend across the nucleus. The basal bodies migrate towards the poles early in division. Microtubules are not present between the nucleus and the basal bodies. Chromosomal separation is accomplished by sliding of non-chromosomal microtubules and by elongation of the nuclear envelope. Continued constriction of the envelope and elongation of the nucleus leads to the formation of a dumbbell-shaped nucleus by late telophase followed by the constriction into two daughter nuclei. Chloroplasts and stigma are absent, long trichocysts present. Cytoplasm appears in the light microscope refractive, the cells have a roseate to pink color. Nutrition is by phagotrophy, various preys are ingested. The prey is captured and engulfed, a Dunaliella primolecta Butcher cell digested in about 12 to 24 hrs. Several prey cells may be ingested . During digestion the prey first becomes more electron-dense and the contents coagulate. Later the prey disintegrates and the remains of several prey items may be enclosed in one food vacuole. The prymnesiophyte Isochrysis galbana Parke is a better food resulting in a higher growth rate than the diatom Phaeodactylum cornutum Bohlin. The degradation of the algal pigments is more slowly than the ingestion rate. Oxyrrhis is one of the few obligate heterotrophic dinoflagellates which can be cultivated without addition of particulate food. It has an absolute requirement for a quinone and one for a steroid. Spherical vegetative cysts, about 10 &m in diam., were produced in a tidal rhythm in a population living in a rock pool. Habitat: Marine, from brackish to hyperhaline; neritic in coastal waters with decaying organic material and in rock-pools. Develop very often in seawater aquaria. Apparently world-wide, except in polar waters. The systematic position of Oxyrrhis is under discussion. There is more and more evidence, that Oxyrrhis is an early divergence sister to the dinoflagellates and in a recent classification of the dinoflagellates (Fensome and others 1993) Oxyrrhis is excluded from this group, based on the type of mitosis and also the structure of the transverse flagellum. Also molecular genetic analysis apparently support the early divergence of Oxyrrhis (Lennaers and others 1991).
Information contributed by: M. Elbrächter. The most recent alteration to this page was made on 2017-05-22 by M.D. Guiry.
Taxonomic status: This name is of an entity that is currently accepted taxonomically.
Most recent taxonomic treatment adopted: Kawai, H. & Nakayama, T. (2015). Introduction (Heterokontobionta p.p.), Cryptophyta, Dinophyta, Haptophyta, Heterokontophyta (except Coscinodiscophyceae, Mediophyceae, Fragilariophyceae, Bacillariophyceae, Phaeophyceae, Eustigmatophyceae), Chlorarachniophyta, Euglenophyta. In: Syllabus of plant families. Adolf Engler's Syllabus der Pflanzenfamilien. Ed. 13. Phototrophic eukaryotic Algae. Glaucocystophyta, Cryptophyta, Dinophyta/Dinozoa, Haptophyta, Heterokontophyta/Ochrophyta, Chlorarachnniophyta/Cercozoa, Chlorophyta, Streptophyta p.p. (Frey, W. Eds), pp. 11-64, 103-139. Stuttgart: Borntraeger Science Publishers.
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Some of the descriptions included in AlgaeBase were originally from the unpublished Encyclopedia of Algal Genera, organised in the 1990s by Dr Bruce Parker on behalf of the Phycological Society of America (PSA) and intended to be published in CD format. These AlgaeBase descriptions are now being continually updated, and each current contributor is identified above. The PSA and AlgaeBase warmly acknowledge the generosity of all past and present contributors and particularly the work of Dr Parker.
Descriptions of chrysophyte genera were subsequently published in J. Kristiansen & H.R. Preisig (eds.). 2001. Encyclopedia of Chrysophyte Genera. Bibliotheca Phycologica 110: 1-260.
Linking to this page: https://www.algaebase.org/search/genus/detail/?genus_id=44571
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 22 May 2017. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 04 December 2023