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Amphitetras are benthic, centric, chain forming diatoms. Most often epiphytic, but frequently suspended in coastal pelagic waters. Triangular or quadrangular, highly silicified valves, with hexagonal areolae a central dome with depressed center. Amphitetras have true ocelli at the angles, by which they possess a rim of silica around a mesh of tiny pores. No rimoportulae reported (Round et al. 1990; Tiffany and Hurwitz 2022). A recent detailed taxonomic description is in Sims et al. (2018).

Species:

Amphitetras antediluviana (Ehrenberg) 1841
Synonyms: According to Algaebase (Guiry and Guiry 2024), Amphitetras antediluviana is the current name and the synonym is Biddulphia antediluviana Ehrenberg 1841. It has also been identified as Triceratium formosum Brightwell (Dexiang et al. 1985). Round et al. (1990) give reasons why B. antediluviana should be placed in Amphitetras C.G. Ehrenberg 1840.

Description:
Amphitetras antediluviana cells are solitary or form short chains, whereby they are connected at the ocelli to form zigzag colonies. Valves are obtuse at the corners and quadrangular with a gentle concavity along the margins. 54–120 μm in width. At each corner is a distinctive true ocellus, with a rim of silica around a mesh of tiny pores. The valve surface is coarsely areolate and arranged in concentric lines in the slightly depressed central area. The girdle is deep with irregular lines of scattered pores. Numerous small oval plate-like chloroplasts. (Hendey 1962: 102; Round et al. 1990: 232-233; Tiffany and Hurwitz 2022).

Salish Sea specimens: Amphitetras antediluviana on Zm-Sidney Spit-ECH-Sandy-Oct 5-2024-TM4000(x600)4.tif; Amphitetras antediluviana(Biddulphia antediluviana)_SHW-0009-_3-Dec 10-09_4.tif; SHW_Biddulphia antediluviana-0004_3-Dec 14-2010.jpg; SHW-5pm-Biddulphia antediluviana-1102_2-Jan 7-09_2.jpg; SHW_Biddulphia antediluviana-0009_2-Dec 14-2010.jpg; Amphitetras antediluviana_SHW-stb1-Biddulphia antediluviana_3_2-July 17-2012_3.tif; Amphitetras antediluviana_SHW-stb1-Biddulphia antediluviana_m001-July 17-2012_3.tif;

Amphitetras antediluviana cells are solitary or form short chains, whereby they are connected at the ocelli to form zigzag colonies. Valves quadrangular with rounded apices and gentle concave margins. 71.1–132.4 μm in width between poles. At each corner is a distinctive true ocellus, with a rim of silica around a mesh of tiny pores. The valve surface is coarsely areolate and arranged in concentric lines in the slightly depressed central area. The girdle is deep with irregular lines of scattered pores. Numerous small oval plate-like chloroplasts.

Amphitetras antediluviana (as Biddulphia antediluviana Ehrenberg 1841) was reported in the Salish Sea, by:
Lord, J. K., (1866). The naturalist in Vancouver Island and British Columbia. In two volumes--Vol. II [B]. Richard Bentley, London. p. 373. doi:http://dx.doi.org/10.14288/1.0222158
Bailey, L.W., and MacKay A.H. (1916). Diatoms from the eastern coast of Vancouver Island. Trans. Roy. Soc. Can. Series 3, Vol. 9(sec. 4): 161. and
In the Strait of Georgia, Shim, J. H. (1976). Distribution and Taxonomy of Planktonic Marine Diatoms in the Strait of Georgia, B.C. Phd. Thesis, UBC. , pp. 154, 214 & 238, Pl. 17, fig. 6.

Methods:

This sample was found on a sun dried section of eelgrass, Zostera marina from Sidney Spit, Sidney Island, near Swartz Bay, Vancouver Island. It was gold coating and imaged in a Hitachi TM4000 table top Scanning Electron Microscope (SEM) on loan by Hitachi HiTec Canada to Elaine Humphrey, at the Advanced Microscopy Facility, UVIC. Imaged by Elaine and Sandy during the Oct. 5, 2024 IMERSS Symposium. Taxonomy and adjustments to the image by Mark Webber (imerss.org).

References:

Dexiang, J., Zhaodhi, C., Junmin, L., and Shicheng, L. (1985) Marine Benthic Diatoms in China, Vol.1. China Ocean Press, Beijing and Spinger-Verlag, Berlin. p.54 and plate 13, figure 95.

Guiry, M.D. in Guiry, M.D. & Guiry, G.M. 2020. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org; searched on 16 January 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.

Jahn, R. and Kusber, W.-H., (2006). Algae of the Ehrenberg collection-3. Typification of seven diatom taxa described by C G. Ehrenberg predominantly from Greece. Wildenowia, 6, 527–535.

Liebisch, W., (1928). Amphitetras antediluviana Ehrbg., sowie einige Beitr.ge zum Bau und zur Entwicklung der Diatomeenzelle. Z. Bot., 20, 225–271, , (In German).

Mayama, S. and Fujita, D. (1995) Two types of areola occlusion in the valve of Amphitetras antediluviana Ehrenberg. Diatom 11: 25–29. (In Japanese).

Metzeltin, D. & García-Rodríguez, F. (2003). Las diatomeas uruguayas. pp. [1]-210, 74 pls. Uruguay: DIRAC Facultad de Ciencias, Universidad de la República.

Round, F.E., Crawford R.M., Mann, D.G. (1990). The Diatoms, Biology & Morphology of the Genera, p. 232-233. Cambridge University Press, Cambridge, UK.

Sims, P. (ed), (1996), An Atlas of British Diatoms, p. 594. BioPress Ltd. Bristol.

Sims, P.A., Williams, D.M. & Ashworth, M. P. (2018). Examination of type specimens for the genera Odontella and Zygoceros (Bacillariophyceae) with evidence for the new family Odontellaceae and a description of three new genera. Phytotaxa 382(1): 1-56, 156 figs, 2 text-figs.

Tiffany, M. and Hurwitz, B. (2022). Valve Morphogenesis in Amphitetras antediluviana Ehrenberg. In, Diatom Morphogenesis. Annenkov, V., Seckback, J. and Gordon, R. (ed.). Wiley. Scrivener Publishing, Beverly, Massachusetts.