Species identified:
Shionodiscus poro-irregulatus (Hasle & Heimdal 1970) Alverson, (Kang et Theriot (2006)
Genus:
Taxonomic classification:
Phylum: Heterokontophyta
Subphylum: Bacillariophytina
Class: Medioiophyceae
Subclass: Thalassiosirophycidae
Order: Thalassiosirales
Family: Thalassiosirosiraceae
Genus: Shionodiscus (Guiry and Guiry 2024)
Type species: Shionodiscus oestrupii (Ostenfeld) A.J.Alverson, S.-H.Kang & E.C.Theriot 2006: 258 (Guiry and Guiry 2024)
Genus Summary:
A small marine genus similar in appearance to Thalassiosira Cleve. However, it differs from the later genus by the labiate process always being some distance from the margin, normally on the valve face, occasionally near the edge of the face. The strutted processes are typically long inward extensions and always the outward extensions are reduced or absent (Hasle and Syvertsen
1996; Alverson et al. 2006; Wilks and Armand 2017).
Species:
Shionodiscus poro-irregulatus (Hasle & Heimdal 1970)
Alverson, (Kang et Theriot (2006)
Thalassiosira proro-irregulata Hasle & Heimdal 1970
(Hasle & Heimdal, 1970, p. 573-574, Fig. 55-64, 71, 72.)
Description:
Girdle view: Diameter 21-30 µm. Valves flat, slightly depressed at the center, with slightly rounded edges. Cells close together in chains. Distances between cells about one-fifth of the pervalvar axis and less than one-fourth of the diameter. Chloroplasts numerous. Valve view: Valve areolae is 10 - 15 in 10 µm. Hexagonal areolae, approximately same size throughout the valve. Inner sieve membrane of areolae has numerous small pores close together. 1-8 central trifultate strutted processes, independent of cell size, irregularly scattered in the valve centre. Marginal processes, internally long, not extending on exterior of the frustule, 4-6 in 10 µm. Marginal processes situated vertically on a high and steep mantle. Labiate process located mid-way between margin and center. Labiate process is notably anvil shaped. Labiate process is 5-6 areolae from central process. (Hasle and Heimdal 1970; Hasle and Syvertsen, 1996; Kang et Theriot 2006; Guiry and Guiry 2024)
Salish Sea specimens: Shionodiscus poro-irregulatus Gen Plank (THAL)-Box 19 June 25-2022-TM4000_nitric-Aug 14-2022_ Stb Site 1b_60(x3k)4.tif; Shionodiscus poro-irregulatus-Gen Plank-Porlier-(THAL)-Box 19 June 25-2022-TM4000_nitric-Aug 14-2022 Stb Site 1b_57(x1.8k)_4.tif.
Morphometric data:
Girdle view: Diameter 21.9-37.5 µm. Valves flat, slightly depressed at the center, with slightly rounded edges. Valve view: Valve areolae is 8-12 in 10 µm. Hexagonal areolae, approximately same size throughout the valve. 2-5 central trifultate strutted processes irregularly scattered in the valve centre. Marginal processes, internally long or short, but not extending on exterior of the frustule, 4-5 in 10 µm. Marginal processes situated vertically on a high and steep mantle. Marginal processes are 1.8-2.4 µm apart. Labiate process located 50-60% towards centre of valve. Labiate process is notably anvil shaped. Labiate process is 5-6 areolae from central process.
This is a first report of Shionodiscus poro-irregulatus in the Salish Sea and Pacific Western Canada.
From a general 60 µm mesh plankton tow at Porlier Pass, Galiano Island, BC, Canada, on June 25, 2022. After 4% formalin (final concentration) fixation, cells were cleaned with concentrated nitric acid on 12 mm glass coverslips and rinsed in distilled water deionized water. Mounted with double sided taper to 13 mm aluminum SEM stubs. Thank you to Andrew Simon of IMERSS for collecting the sample. SEM imaging with a Hitachi TM4000 at the Advanced Microscope Facility, UVIC. Thank you Hitachi HiTech and Elaine Humphrey for SEM support. Images by Arjan an Asselt, Melanie Quenneville and Mark Webber. Specimen preparation, imaging and taxonomy by Mark Webber (imerss.org).
References:
Alverson, A.J., Kang, S.-H. & Theriot, E.C. (2006). Cell wall morphology and systematic importance of Thalassiosira ritscheri (Hustedt) Hasle, with a description of Shionodiscus gen. nov. Diatom Research 21(2): 215-262.
Fryxell, G. A., & Hasle, G. R. 1979. The genus Thalassiosira: T. trifulta sp. nova and other species with tricolumnar supports on strutted processes. Beiheft zur Nova Hedwigia 64:13-32.
Fryxell, G. A., & Hasle, G. R. (1980). The marine diatom Thalassiosira oestrupii" Structure, taxonomy and distribution. American Journal of Botany 67:804-814.
Hasle, G.R. & Syvertsen, E.E. (1996). Marine Diatoms. In: Identifying Marine Phytoplankton. (Tomas, C.R. Eds). San Diego: Academic Press.
Guiry, M.D. & Guiry, G.M. 2007, AlgaeBase version 4.2. World-wide electronic publication, National University of Ireland, http://algaebase.org, searched March 15, 2024.
Li, Y. and Lu, S. (2013). The genus Thalassiosira off the Guangdong coast, South China Sea. Botanica Marina; 56(1): 83–110. DOI: 10.1515/bot-2011-0045
Wilks, J. V. and Armand, L. K. (2017): Diversity and taxonomic identification of Shionodiscus spp. in the Australian sector of the Subantarctic Zone, Diatom Research, DOI: 10.1080/0269249X.2017.1365015
Rock on coast. Quadra Island, BC, Canada
Batwing Vinyl. Rock on shore. Quadra Island, BC, Canada
Larger, thicker thallus, on seeping rock.