chlorophilia's Identifications

Species identified:

Isthmia enervis Ehrenberg 1838: 209, pl. 16, fig. 6

Genus: Isthmia Agardh, C.A. (1832).
Taxonomic classification:

Phylum: Bacillariophyta,
Subphylum: Bacillariophytina,
Class: Mediophyceae,
Subclass: Chaetocerotophycidae,
Order: Hemiaulales,
Family: Isthmiaceae,
Genus: Isthmia (Guiry & Guiry, 2020).

Samples from the Salish Sea as part of the Salish Sea Diatom Project (imerss.org)

Genus and species description for both I. enervis and I. nervosa:

The genus is heteropolar, where one valve is more elevated than the other. Isthmia species are found in both trapezoidal and rombhoidal forms. Valves are oval with no distinct transition from valve to mantle. Isthmia nervosa valve apical axis 100-280 µm long, width 30-50 µm, length of whole frustule in girdle view is maximum 280 µm Isthmia enervis valve apical axis 48-200 µm long, length of whole frustule in girdle view is 150-300 µm (Cupp 1943: 166; Hendey 1964: 110). Both I. nervosa and I. enervis have only one pseudocellus per cell, a bulbous extension in which a cluster of small areolae are seen. The areolae cluster is far more pronounced in I. nervosa than I. enervis: the areolae being smaller in size in I. enervis, and the areolae suddenly reduces in size at the pole of the pseudocellus of I. nervosa. It is proposed that the pores behind the apex of the pseudocellus secrete a mucilage pad by which the cell attaches to the host, though areolae of the pseudocellus may also be involved. The costae (rib-like thickenings) are the distinctive “nerves” of I. nervosa. The cribra (plates with pores) in I. nervosa vary over the valve face unlike I. enervis where the cribra are more regular.

Both species may have a U-shaped notch on the distal end of the girdle band (copula). However, it is far less obvious in I. nervosa, but more or less a distinctive feature of the epivalve of trapezoidal cells of I. enervis. Round (1984) notes that on some cells of I. enervis the girdle band notch could not be detected. I. nervosa has very prominent struts supporting the girdle diaphragm, less so for I. enervis. Isthmia, a small genus, and a coastal marine diatom are colonial and epiphytic on seaweeds. It is both highly silicified and large relative to other diatoms. Many diatom taxonomists have placed Isthmia in the Biddulphiaceae, though there are complexities to its characteristics and hard to place in the centric group (Kützing, 1844; W.Smith 1856: Plate 47 Fig. F.; Van Heurck 1880-1881: XCVI, fig. 1-3.; Hendey 1964: 110-111, Pl. XXV, fig. 3 and Pl. XXV, fig. 2; Round 1984; Round et al. 1990; Sims (1996); Guiry and Guiry 2020).

Isthmia enervis Ehrenberg 1838: 209, pl. 16, fig. 6
Salish Sea specimens: Isthmia enervis on Zm SI-TM4000 ECH Zm Nov 3-2021 (MW)(x80)_3b.tif; Isthmia enervis on Zm SI-TM4000 ECH Zm Nov 3-2021 (MW)(x150)_2.tif; Isthmia enervis on Zm SI-TM4000 ECH Zm Nov 3-2021 (MW)_3(x300)_2.tif; Isthmia enervis on Zm SI-TM4000 ECH Zm Nov 3-2021 (MW)_4(x400)_2.tif; Isthmia enervis on Zm SI-TM4000 ECH Zm Nov 3-2021 (MW)_7(x600)_2.tif; Isthmia enervis on Zm Sidney Isl-En-TM4000 ECH Zm Nov 3-2021 (MW)_10(x800k)_2.tif; Isthmia enervis on Zm Sidney Isl-TM4000 ECH Zm Nov 3-2021 (MW)_9(x1.0k)_2.tif.
Description and morphometric data:
Rhomboid shaped cells, heteropolar. Elliptical, ovoid valves, apical axis 70 (48-200) µm, length of whole frustule in girdle view is 195-268 (150-300) µm. No transition between valve face and mantle. A single pseudocellus per cell, with a cluster of smaller areolae. Externally, large areolae, cribrate, suspended by struts, ovoid to quadrate, enclosed by robust silica. Every 2-3 areolae in the apical direction there is a pore in the silica mesh framework and 1-2 areolae between poroids in the transapical direction. Areolae pattern curved, slightly radiate transapically, 2-3 in 10 µm. Areolae size more or less regular over valve becoming smaller at pseudocellus (center of ocelli are obscured in this specimen). Girdle bands complete, with smaller areolae than valve and closed by cribra. No notch observed in the epitheca copula (possibly obscured, an irregular feature). No internal valves imaged. Forms branching colonies with large mucilage pads

This a first report for Isthmia enervis found in Western Canada and the Salish Sea.

Methods:

Isthmia enervis was found on a floating section of the eelgrass, Zostera marina, on surface waters, north west of Sidney Island, Sidney, BC, Canada. The eelgrass was left to dry naturally in summer conditions, then 10 mm sections were cut and attached by a carbon sticky to an SEM stub. Collected and prepared by Elaine Humphrey, of the Advanced Microscope Facility (AMF), University of Victoria (UVIC), BC. Canada. Imaging on a Hitachi TM4000Plus desktop SEM on loan to Elaine Humphrey by Hitachi HiTech Canada for educational outreach. Imaging, taxonomy and imaging adjustments by Mark Webber.

References:

Agardh, C.A. (1832). Conspectus Criticus Diatomacearum. Part 4. pp. 49-66.Lundae [Lund]: Literis Berlingianus.

Baker, A.L. et al. 2012. Phycokey-- an image based key to Algae (PS Protista), Cyanobacteria, and other aquatic objects. University of New Hampshire Center for Freshwater Biology. (searched Feb 26, 2024)
http://cfb.unh.edu/phycokey/Choices/Bacillariophyceae/Centric/Centric_Unicells/ISTHMIA/Isthmia_key.html

Cupp, E. E. (1943). Marine Plankton Diatoms of the West Coast of North America. Bull. Scrips. Inst. Oceanography. 5: 1-238.

Dickman, M., Hodgkiss, J., Cheng, Z. and Gao, Y. Diatoms from the South China Sea. Searched July 4, 2020. http://121.192.179.196/diatom/diatomphoto/Centric%20diatoms/htmldir/0000026e.htm

Guiry, W. in Guiry, M.D. & Guiry, G.M. 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 03 July 2020.

Hendey, N.I. (1964). An introductory account of the smaller algae of British coastal waters. Part V: Bacillariophyceae (diatoms). pp. [i]-xxii, 1-317. London: Ministry of Agriculture, Fisheries and Food, Fishery Investigations. Her Majesty’s Stationery Office.

Kützing, F.T. (1844). Die Kieselschaligen Bacillarien oder Diatomeen. pp. [i-vii], [1]-152, pls 1-30. Nordhausen: zu finden bei W. Köhne.

Round, F.E. (1984). Structure of the Cells, Cell Division and Colony Formation in the Diatoms Isthmia enervis Her. and I. nervosa Kütz. Annals of Botany 53, 457-468.

Round, F. E., Crawford, R. M. and Mann, D. G. (1990). The Diatoms, Biology & Morphology of the Genera, p. 142-142. Cambridge University Press, Cambridge, UK.

Shim, J. H. (1976). Distribution and Taxonomy of Planktonic Marine Diatoms in the Strait of Georgia, B.C. Phd. Thesis, UBC. P. 157. Plate XIX no. 1.

Sims, P.A. (ed.) (1996). An atlas of British diatoms arranged by B. Hartley based on illustrations by H.G. Barber and J.R. Carter. pp. [2], 1-601, incl. 290 pls. Bristol: Biopress Ltd.

Smith (1856). British Diatomaceae Vol.2

Guiry, W. in Guiry, M.D. & Guiry, G.M. 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 03 July 2020.

Van Heurck, H. (1880-1881). Synopis des Diatomees de Belgiue. Edite par L’

Wolle, F. (1894). Diatomaceae. The Comenius Press. Bethlehem. PA.

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