Platysulcus

Platysulcus (from Latin platy 'wide', and sulcus 'furrow') is an eukaryotic microorganism that was recently discovered to be the earliest diverging lineage of the Heterokont phylogenetic tree.[1] It is the only member of the family Platysulcidae, order Platysulcida and class Platysulcea, of uncertain taxonomic position within the phylum Bigyra.[2] It contains the only species P. tardus.

Platysulcus
Scientific classification Edit this classification
Domain: Eukaryota
Clade: Diaphoretickes
Clade: SAR
Clade: Stramenopiles
Phylum: Bigyra
Class: Platysulcea
Cavalier-Smith, 2017
Order: Platysulcida
Cavalier-Smith, 2017
Family: Platysulcidae
Shiratori, Nkayama & Ishida, 2015
Genus: Platysulcus
Shiratori, Nakayama & Ishida, 2015
Species:
P. tardus
Binomial name
Platysulcus tardus
Shiratori, Nkayama & Ishida, 2015

Morphology

Platysulcus is a gliding biflagellate, with a short anterior flagellum, a long posterior flagellum, and a flagellar apparatus typical of stramenopiles. It has tubular mastigonemes on the anterior flagellum. It contains mitochondria with tubular cristae. The basal body and the transitional region of the flagella lack ring-shaped or helical structures. The two flagellar roots consist of 11 microtubules forming an “L”-shape.[1]

Its cells are oval or ovoid in shape, around 5.62 μm in length and 3.76 μm in width. The anterior flagellum is around 9 μm in length, and the posterior measures around 17 μm. They contain extrusomes and a large, flat vesicle surrounding the cytoplasm where the nucleus, mitochondria, and microbodies are found.[1]

Ecology

Platysulcus was isolated from sedimented detritus on seaweed collected near Ngeruktabel Island, Palau. It is a free-living phagotrophic protist, bacterivorous and marine.[1]

Phylogeny and taxonomy

Phylogeny

Phylogenetic analyses recover Platysulcea as the earliest diverging lineage of Stramenopiles, sister to a clade containing Bigyra and Gyrista.[3]

Stramenopiles
Gyrista

Ochrophyta

Pseudofungi

Bigyromonadea

Bigyra

Sagenista

Opalozoa

Platysulcus tardus

Taxonomy

Despite the phylogenetic results, Platysulcea has been classified as part of the phylum Bigyra.[2]

  • Class Platysulcea Cavalier-Smith, 2017
    • Order Platysulcida Cavalier-Smith, 2017
      • Family Platysulcidae Shiratori, Nkayama & Ishida, 2015
        • Platysulcus Shiratori, Nkayama & Ishida, 2015
          • P. tardus Shiratori, Nkayama & Ishida, 2015

References
  1. Shiratori, Takashi; Nakayama, Takeshi; Ishida, Ken-ichiro (2015). "A New Deep-branching Stramenopile, Platysulcus tardus gen. nov., sp. nov". Protist. 166 (3): 337–348. doi:10.1016/j.protis.2015.05.001. hdl:2241/00148461. ISSN 1434-4610. PMID 26070192.
  2. Cavalier-Smith, Thomas (5 September 2017). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/s00709-017-1147-3. PMC 5756292. PMID 28875267.
  3. Thakur R, Shiratori T, Ishida KI (November 2019). "Taxon-rich Multigene Phylogenetic Analyses Resolve the Phylogenetic Relationship Among Deep-branching Stramenopiles". Protist. 170 (5): 125682. doi:10.1016/j.protis.2019.125682. PMID 31568885.
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