Hydrodictyon Roth, 1797, nom. cons.

Holotype species: Hydrodictyon reticulatum (Linnaeus) Bory

Original publication and holotype designation: Roth, A.W. (1797). Bemerkungen über das Studium der cryptogamischen Wassergewächse. pp. [1]-109, [+1 Druckfehler]. Hannover: bei den Gebrüdern Hahn.

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Description: Thalli coenobial, macroscopic, mostly 20 (-40) cm in length when mature, comprised of cylindrical or broadly ovoid cells, to 1 cm long when mature, joined at ends to form cylindrical net closed at poles. Within network, individual net units comprised of 3-9 (mostly 6) cells, with cell number species specific. Cells highly multinucleate; chloroplast forming a parietal reticulum around large central vacuole; pyrenoids numerous. Nuclei generally dispersed but aggregations associated with localized growth. Asexual reproduction by autocolony formation present in most species. Cytokinesis simultaneous within parental cell to produce all cells required for new colony; naked zoospores biflagellate, spherical to ovoid and uninucleate, formed in peripheral cytoplasm. The vacuole, vacuolar membrane and cell wall form a 'mold' within which new nets are organized. After accumulation and free-swimming stage within parental cell, zoospores change shape from oval to rhomboidal, align with each other, and gradually withdraw flagella and form new colonies. Zoospores with highly localized arrays of parallel microtubules; contact between zoospores during net formation at microtubule sites. Mitochondria vary with life history stage; mature cells mostly with more or less continuous network of mitochondria, zoospores with many small spherical mitochondria clustered at the base of flagella during active swimming. Sexual reproduction studied in detail in H. reticulatum. Gametes isogamous, uninucleate and biflagellate, with apical cap; when first formed gametes swim freely in cell lumen. Gametes superficially similar to zoospores but differ in size (typically smaller), and absence of parallel microtubules under plasma lemma. Gametes shed through pore in parental cell wall and fusion occurs. Zygotes initially quadriflagellate but withdraw flagella and secrete cell wall to form zygospores. Zygospores undergo meiosis and form 4-8 uninucleate zoospores that produce uninucleate, nonflagellated polyhedral stage. Non fused gametes may produce smaller azygospores which germinate to produce single zoospores that develop as in meiotic zoospores. Polyhedral cells undergo mitosis and cytoplasmic cleavage to form numerous zoospores that retract flagella and form new net. After gelatinization of cell wall, germ net released. Typically germ net flat with 100-300 cells. After asexual reproduction cylindrical nets typically produced. Hydrodictyon planktonic, in lakes and slowly moving streams, mostly in hard water. Reported in temperate to tropical conditions; on all continents except Antarctica. Ultrastructure of zoospores links Tetraedron as possible sister group of Hydrodictyon and other members of family. Species distinguished based on differences in net morphology and size and arrangement of cells. In some treatments Hydrodictyaceae assigned to Protosiphonales.

Information contributed by: D. Garbary & T. Harper. The most recent alteration to this page was made on 2024-05-20 by M.D. Guiry.

Taxonomic status: This name is of an entity that is currently accepted taxonomically.

Gender: This genus name is currently treated as neuter.

Most recent taxonomic treatment adopted: John, D.M. & Tsarenko, P.M. (2002). Order Chlorococcales. In: The Freshwater Algal Flora of the British Isles. An identification guide to freshwater and terrestrial algae. (John, D.M., Whitton, B.A. & Brook, A.J. Eds), pp. 327-409. Cambridge: Cambridge University Press.

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Contributors
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=43413

Citing AlgaeBase
Cite this record as:
M.D. Guiry in Guiry, M.D. & Guiry, G.M. 20 May 2024. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. https://www.algaebase.org; searched on 25 November 2024