Diatoms are an important and diverse group of organisms that fix almost 20% of global carbon (^{Armbrust, 2009}; ^{Malviya et al., 2016}; D. G. ^{Mann, 1999}; ^{Onuma et al., 2017}). However, aside from the toxic diatoms, the taxonomy of the specious class of Bacillariophyceae is ‘in a rather poor state’ (^{Mann et al., 2020}). The taxonomic history of the genus Halamphora has been dynamic since its revival by ^{Levkov (2009)} produced a considerable number of inclusions via transfers of species new nomenclatural combinations, mostly from the genus Amphora, descriptions of new species, and taxonomic validations. The increased number of taxonomically accepted species and intraspecific names registered in Algaebase is remarkable, from 110 in 2018 to 163 in 2023 (^{Guiry & Guiry 2023}), which reflects the degree of complexity that this genus still represents.

• ^{Armbrust, 2009}
  The life of diatoms in the world’s oceans

  Nature, 2009
  Armbrust, E. V. (2009). The life of diatoms in the world’s oceans. Nature, 459(7244), 185-192. https://doi.org/10.1038/nature08057
• ^{Malviya et al., 2016}
  Insights into global diatom distribution and diversity in the world’s ocean

  Proceedings of the National Academy of Sciences of the United States of America, 2016
  Malviya, S., Scalco, E., Audic, S., Vincent, F., Veluchamy, A., Poulain, J., Wincker, P., Iudicone, D., De Vargas, C., Bittner, L., Zingone, A., & Bowler, C. (2016). Insights into global diatom distribution and diversity in the world’s ocean. Proceedings of the National Academy of Sciences of the United States of America, 113(11), E1516-E1525. https://doi.org/10.1073/PNAS.1509523113/DCSUPPLEMENTAL/PNAS.1509523113.SAPP.PDF
• ^{Mann, 1999}
  The species concept in diatoms

  Phycologia, 1999
  Mann, D. G. (1999). The species concept in diatoms. Phycologia, 38(6), 437-495. https://doi.org/10.2216/i0031-8884-38-6-437.1
• ^{Onuma et al., 2017}
  Regulation of chloroplast and nucleomorph replication by the cell cycle in the cryptophyte Guillardia theta

  Scientific Reports, 2017
  Onuma, R., Mishra, N., & Miyagishima, S. (2017). Regulation of chloroplast and nucleomorph replication by the cell cycle in the cryptophyte Guillardia theta. Scientific Reports, 7(2345). https://doi.org/10.1038/s41598-017-02668-2
• ^{Mann et al., 2020}
  Ripe for reassessment: A synthesis of available molecular data for the speciose diatom family Bacillariaceae

  Molecular Phylogenetics and Evolution, 2020
  Mann, D., Trobajo, R., Sato, S., Li, C., Witkowski, A., Rimet, F., Ashworth, M., Hollands, R., & Theriot, E. (2020). Ripe for reassessment: A synthesis of available molecular data for the speciose diatom family Bacillariaceae. Molecular Phylogenetics and Evolution, 158, 106985. https://doi.org/10.1016/j.ympev.2020.106985
• ^{Levkov (2009)}
  Amphora sensu lato

  Diatoms of Europe: Diatoms of the Europe inland waters and comparable habitats, 2009
  Levkov, Z. (2009). Amphora sensu lato. In H. Lange-Bertalot (Ed.), Diatoms of Europe: Diatoms of the Europe inland waters and comparable habitats (p. 916). A.R.G. Gantner Verlag K. G.
• ^{Guiry & Guiry 2023}
  AlgaeBase. World-wide electronic publication, 2023
  Guiry, M. D. & Guiry, G. M. (2023) AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org ; searched on 8 may 2023.

In diatom, monoclonal cultures form a vital part of an integrative taxonomic approach to identifying species using morphological and molecular data (^{Mohamad et al., 2022}). Also, electron microscopy of monoclonal cultures is commonly used to describe new diatom species with ultrastructural details. ^{Stepanek & Kociolek (2018)} described H. adumbratoides and complemented their description with molecular tools. Electron microscopy and molecular information have contributed significantly to the determination of new species of diatoms, taxonomic validations, and the transfer of taxa from one genus to another. For example, taxonomic relocations of taxa have been carried out with the closely related genera Amphora, Cymbamphora, and Seminavis (^{Levkov, 2009}; ^{Stepanek & Kociolek, 2013}; ²⁰¹⁵, ²⁰¹⁸, ²⁰¹⁹; ^{Van de Vijver et al., 2014}).

• ^{Mohamad et al., 2022}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346
• ^{Stepanek & Kociolek (2018)}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.
• ^{Levkov, 2009}
  Amphora sensu lato

  Diatoms of Europe: Diatoms of the Europe inland waters and comparable habitats, 2009
  Levkov, Z. (2009). Amphora sensu lato. In H. Lange-Bertalot (Ed.), Diatoms of Europe: Diatoms of the Europe inland waters and comparable habitats (p. 916). A.R.G. Gantner Verlag K. G.
• ^{Stepanek & Kociolek, 2013}
  Several new species of Amphora and Halamphora from the western USA

  Diatom Research, 2013
  Stepanek, J. G., & Kociolek, J. P. (2013). Several new species of Amphora and Halamphora from the western USA. Diatom Research, 28(1), 61-76. https://doi.org/10.1080/0269249X.2012.735205
• ²⁰¹⁵
  Three new species of the diatom genus Halamphora (Bacillariophyta) from the prairie pothole lakes region of North Dakota, USA

  Phytotaxa, 2015
  Stepanek, J. G., & Kociolek, J. P. (2015). Three new species of the diatom genus Halamphora (Bacillariophyta) from the prairie pothole lakes region of North Dakota, USA. Phytotaxa, 197, 27-36. https://doi.org/10.11646/phytotaxa.197.1.3
• ²⁰¹⁸
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.
• ²⁰¹⁹
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Van de Vijver et al., 2014}
  Revision of the genus Halamphora (Bacillariophyta) in the Antarctic Region

  Plant Ecology and Evolution, 2014
  Van de Vijver, B., Kopalova, K., Zidarova, R., & Levkov, Z. (2014). Revision of the genus Halamphora (Bacillariophyta) in the Antarctic Region. Plant Ecology and Evolution, 147, 374-391. https://doi.org/10.5091/plecevo.2014.979

Morphometric similarity between taxa of different genera is rare; however, it is not uncommon among species of closely related genera. For example, the morphology of H. adumbratoides is very similar to that of Amphora adumbrata in terms of the shape of the valve and the fine striae composed of a single elongated areola (^{Stepanek & Kociolek, 2018}). The number of striae was a key characteristic for differentiating these taxa by traditional taxonomy (morphology) (^{Desianti et al., 2015}; ^{Stepanek & Kociolek, 2018}). At the molecular level, SSU, rbcL, and psbC markers were used to identify H. adumbratoides (^{Stepanek & Kociolek, 2018}).

• ^{Stepanek & Kociolek, 2018}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.
• ^{Desianti et al., 2015}
  Examination of the type materials of diatoms described by Hohn and Hellerman from the Atlantic Coast of the USA

  Diatom Research, 2015
  Desianti, N., Potapova, M., & Beals, J. (2015). Examination of the type materials of diatoms described by Hohn and Hellerman from the Atlantic Coast of the USA. Diatom Research, 30, 1-24. https://doi.org/10.1080/0269249X.2014.1000020
• ^{Stepanek & Kociolek, 2018}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.
• ^{Stepanek & Kociolek, 2018}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.

In geographical terms, H. adumbratoides has been recorded only from the coasts of the Atlantic Ocean, in Florida Bay, Cotton Key, Monroe Country, FL, USA. In this publication, we present morphological characteristics and use molecular identity of this taxon (strain CIBA 160) to report its presence in the Pacific Ocean region from the coastal Balandra lagoon (La Paz Bay) in the Gulf of California, on the southern coast of the Baja California Peninsula, Mexico. It is the second recording but the first interoceanic registration of H. adumbratoides. We also register considerable morphological features and morphometry variations in the laboratory-cultured cells.

Water samples of 50 mL were taken by triplicate from the Balandra lagoon (24°19′9.01′′N 110°19′18.17′′ W) near La Paz, Baja California Sur (Figure 1), in December 2018, and brought to the laboratory. The samples were filtered through a 30-μm Nitex mesh and f/2 medium with silicates added to the filtered samples (^{Guillard, 1975}).

• ^{Guillard, 1975}
  Culture of Phytoplankton for Feeding Marine Invertebrates

  Culture of Marine Invertebrate Animals, 1975
  Guillard, R. R. L. (1975). Culture of Phytoplankton for Feeding Marine Invertebrates. In M.L. Smith & M.H. Chanley (Eds.), Culture of Marine Invertebrate Animals (pp. 29-60). Plenum Press. https://doi.org/10.1007/978-1-4615-8714-9_3

After two weeks, microalgal cells were isolated in a 1:50 dilution in f/2 medium and streaked on marine agar plates containing the same medium. Single-cell colonies were isolated under low magnification in a microscope, with a sterile hypodermic needle and then transferred to 24-well plates containing 2 ml of culture medium. Two weeks later, the cells were transferred to test tubes with 5 ml of culture medium, and the unialgal culture of isolated cells was examined under light microscopy. Once confirmed, the monoclonal cultures were deposited in CIBNOR’s Microalgae Collection under catalog number CIBA 160 (https://www.cibnor.gob.mx/investigacion/colecciones-biologicas/coleccion-de-microalgas) after three reseeding periods. We have a collection of three fixed slides with the skeletons of the cells, that remains in the laboratory.

For light and electron microscopy and molecular analyses, cells were cultured in triplicate in 500-mL flasks with 250 mL of medium at 25±1°C, 40 μmol·m^-2·s^-1, 12:12 h, and 35 PSU. At the exponential stage (on the sixth day), separate samples were taken for each analysis. Live and cleaned cells were observed under a Zeiss Axio Lab A1 microscope, and photographs were taken with a Canon EOS Rebel T5i camera (Figure 2). The cells were prepared for scanning electron microscopy (SEM) as indicated previously by ^{López-Fuerte et al. (2020)}. Briefly, the organic matter was eliminated by oxidation, heat-assisted with concentrated nitric acid. The cells were then washed in distilled water to reach a neutral pH. SEM images of the cells were taken with a Hitachi SU3500 electron microscope operating at 10 kV and a 6-mm working distance. A coverslip holding the cells was attached to a 32-mm aluminum stub using conductive carbon tape and coated with around 15 nm of gold in a Hummer 6.2 sputtering unit.

• ^{López-Fuerte et al. (2020)}
  Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico

  Phytotaxa, 2020
  López-Fuerte, F. O., Sala, S. E., Lora-Vilchis, M. C., & Murugan, G. (2020). Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico. Phytotaxa, 451(2), 132-144. https://doi.org/10.11646/phytotaxa.451.2.3

The key morphological characteristics -length, width, and density of the striae- were measured by light and electron microscopy and compared to those reported for Halamphora adumbratoides (^{Stepanek & Kociolek, 2018}). The validity nomenclatural status of the name was verified on the Algaebase website (^{Guiry & Guiry 2023}).

• ^{Stepanek & Kociolek, 2018}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.
• ^{Guiry & Guiry 2023}
  AlgaeBase. World-wide electronic publication, 2023
  Guiry, M. D. & Guiry, G. M. (2023) AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. http://www.algaebase.org ; searched on 8 may 2023.

Cells of the CIBA 160 strain obtained from the exponential stage cultures were utilized to extract genomic DNA by the CTAB method (^{Doyle, 1991}; ^{Herrera et al., 2014}). Four regions of DNA were analyzed: fragment of two nuclear genes, the small sub-unit of nuclear gene 18S ribosomal RNA (SSU), and the large subunit of nuclear gene 28S ribosomal RNA (LSU) were amplified following the PCR conditions described in ^{López-Fuerte et al. (2020)}. A partial sequence of the ribulose bisphosphate carboxylase/oxygenase gene (rbcL) from the chloroplast was amplified according to the published protocols (^{López-Fuerte et al., 2020}). Also, the photosystem II CP43 protein gene (psbC) was amplified with 30 picomoles of the psbC+ and psbC- primers (^{Alverson et al., 2007}) in 40 μL of a PCR reaction mixture containing genomic DNA, 0.3 mM dNTPs, 2 mM MgCl₂, 4 μL of 10X PCR buffer, and 2 units of platinum Taq polymerase (Invitrogen^TM).

• ^{Doyle, 1991}
  DNA Protocols for Plants BT

  Molecular Techniques in Taxonomy, 1991
  Doyle, J. (1991). DNA Protocols for Plants BT. In G. M. Hewitt, A. W. B. Johnston, & J. P. W. Young (Eds). Molecular Techniques in Taxonomy. NATO ASI Series (Series H: Cell Biology), vol 57. Springer Berlin Heidelberg (pp. 283-93). https://doi.org/10.1007/978-3-642-83962-7_18
• ^{Herrera et al., 2014}
  Are Prorocentrum hoffmannianum and Prorocentrum belizeanum (DINOPHYCEAE, PROROCENTRALES), the same species? An integration of morphological and molecular data

  Journal of Phycology, 2014
  Herrera, A., Medlin, L., Murugan, G., Sierra, A., Cruz, A., & Hernandez Saavedra, N. (2014). Are Prorocentrum hoffmannianum and Prorocentrum belizeanum (DINOPHYCEAE, PROROCENTRALES), the same species? An integration of morphological and molecular data. Journal of Phycology, 51. https://doi.org/10.1111/jpy.12265
• ^{López-Fuerte et al. (2020)}
  Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico

  Phytotaxa, 2020
  López-Fuerte, F. O., Sala, S. E., Lora-Vilchis, M. C., & Murugan, G. (2020). Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico. Phytotaxa, 451(2), 132-144. https://doi.org/10.11646/phytotaxa.451.2.3
• ^{López-Fuerte et al., 2020}
  Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico

  Phytotaxa, 2020
  López-Fuerte, F. O., Sala, S. E., Lora-Vilchis, M. C., & Murugan, G. (2020). Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico. Phytotaxa, 451(2), 132-144. https://doi.org/10.11646/phytotaxa.451.2.3
• ^{Alverson et al., 2007}
  Bridging the Rubicon: Phylogenetic analysis reveals repeated colonizations of marine and fresh waters by thalassiosiroid diatoms

  Molecular Phylogenetics and Evolution, 2007
  Alverson, A., Jansen, R., & Theriot, E. (2007). Bridging the Rubicon: Phylogenetic analysis reveals repeated colonizations of marine and fresh waters by thalassiosiroid diatoms. Molecular Phylogenetics and Evolution, 45, 193-210. https://doi.org/10.1016/j.ympev.2007.03.024

The PCR conditions for psbC amplification were denaturation at 94°C for 3.30 min, then 35 cycles of 30 s at 94 °C, 50 s at 52 °C, and 80 s at 72 °C. The final extension was for 10 min at 72 °C. Both strands of all markers were sequenced with the amplification primers and an internal primer for the SSU and chloroplast genes (18S 962R, rbcL1255, psbC857).

We edited the four sequences (SSU, LSU, psbC, and rbcL) in DNA Baser 4.5 program (http://www.dnabaser.com) and compared the SSU, rbcL, and psbC sequences to those of H. adumbratoides in the GenBank database. The phylogenetic relationship of the CIBA 160 strain was inferred based on the concatenated nucleotide sequences of SSU, LSU, psbC, and rbcL with 23 Halamphora species (Table 1) using the maximum likelihood (ML) method in PAUP 4.0a166 (^{Swofford, 2002}) and Bayesian inference (BI) in MrBayes 3.2.7a (^{Ronquist et al., 2012}). The best fit nucleotide model TIM3+I+G selected according to the BIC criterion in jModeltest 2.1.10 (^{Darriba et al., 2012}; ^{Guindon & Gascuel, 2003}) for the concatenated nucleotide sequences was implemented in both analyses. Maximum likelihood analysis was performed with 500 pseudoreplicates under the option of heuristic tree-searching with tree bisection-reconnection branch swapping to generate a majority rule ML consensus tree. Bayesian inference was run for 10 million generations, and a majority rule BI consensus tree was obtained after eliminating 25% of the initial trees using the burn-in option.

• ^{Swofford, 2002}
  PAUP*. Phylogenetic Analysis Using Parsimony (*and Other Methods), 2002
  Swofford, D. (2002). PAUP*. Phylogenetic Analysis Using Parsimony (*and Other Methods). Version 4.0b10. In version 4.0b10 edn: Vol. Version 4. Sinauer, Associates, Sunderland. https://doi.org/10.1111/j.0014-3820.2002.tb00191.x
• ^{Ronquist et al., 2012}
  MrBayes 3.2: Efficient Bayesian phylogenetic inference and model choice across a large model space

  Systematic Biology, 2012
  Ronquist, F., Teslenko, M., van der Mark, P., Ayres, D., Darling, A., Höhna, S., Larget, B., Liu, L., Suchard, M., & Huelsenbeck, J. (2012). MrBayes 3.2: Efficient Bayesian phylogenetic inference and model choice across a large model space. Systematic Biology, 61(3), 539-542. https://doi.org/10.1093/sysbio/sys029
• ^{Darriba et al., 2012}
  jModelTest 2: more models, new heuristics and parallel computing

  Nature Methods, 2012
  Darriba, D., Taboada, G., Doallo, R., & Posada, D. (2012). jModelTest 2: more models, new heuristics and parallel computing. Nature Methods, 9, 772. https://doi.org/10.1038/nmeth.2109
• ^{Guindon & Gascuel, 2003}
  A Simple, Fast, and Accurate Algorithm to Estimate Large Phylogenies by Maximum Likelihood

  Systematic Biology, 2003
  Guindon, S., & Gascuel, O. (2003). A Simple, Fast, and Accurate Algorithm to Estimate Large Phylogenies by Maximum Likelihood. Systematic Biology, 52, 696-704. https://doi.org/10.1080/10635150390235520

• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek & Kociolek, 2014}
  Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms

  Protist, 2014
  Stepanek, J. G., & Kociolek, J. P. (2014). Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms. Protist, 165(2), 177-195. https://doi.org/10.1016/j.protis.2014.02.002
• ^{Stephanek et al. 2015}
  Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay

  Phycologia, 2015
  Stepanek, J. G., Mayama, S., & Kociolek, J. P. (2015). Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay. Phycologia , 54, 78-86. https://doi.org/10.2216/14-081.1
• ^{Stepanek & Kociolek, 2014}
  Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms

  Protist, 2014
  Stepanek, J. G., & Kociolek, J. P. (2014). Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms. Protist, 165(2), 177-195. https://doi.org/10.1016/j.protis.2014.02.002
• ^{Stephanek et al. 2015}
  Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay

  Phycologia, 2015
  Stepanek, J. G., Mayama, S., & Kociolek, J. P. (2015). Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay. Phycologia , 54, 78-86. https://doi.org/10.2216/14-081.1
• ^{Stepanek & Kociolek, 2014}
  Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms

  Protist, 2014
  Stepanek, J. G., & Kociolek, J. P. (2014). Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms. Protist, 165(2), 177-195. https://doi.org/10.1016/j.protis.2014.02.002
• ²⁰¹⁸
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.
• ^{Stepanek & Kociolek, 2014}
  Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms

  Protist, 2014
  Stepanek, J. G., & Kociolek, J. P. (2014). Molecular phylogeny of Amphora sensu lato (Bacillariophyta): an investigation into the monophyly and classification of the amphoroid diatoms. Protist, 165(2), 177-195. https://doi.org/10.1016/j.protis.2014.02.002
• ^{Stephanek et al. 2015}
  Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay

  Phycologia, 2015
  Stepanek, J. G., Mayama, S., & Kociolek, J. P. (2015). Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay. Phycologia , 54, 78-86. https://doi.org/10.2216/14-081.1
• ^{Stepanek & Kociolek, 2019}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836
• ^{Stepanek et al., 2015}
  Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay

  Phycologia, 2015
  Stepanek, J. G., Mayama, S., & Kociolek, J. P. (2015). Description and phylogenetic position of Amphora aliformis (Bacillariophyta), a new species from Tokyo Bay. Phycologia , 54, 78-86. https://doi.org/10.2216/14-081.1

The length and width recorded for the valves of the laboratory cultured cells of the strain CIBA 160 (Halamphora adumbratoides) are 4.1-6.6 and 1.6-2.4 μm, respectively. The number of dorsal and ventral striae for the CIBA 160 strain are 57-60 and 60-70 in 10 μm, respectively. The valve shape is semi-elliptical, and the ends are broadly rounded (Figure 3a -j). The raphe is straight with straight proximal ends, while the distal raphe ends are deflected to hooked dorsally (Figure 3a-b). Externally, two pores are visible at the end of the dorsal raphe ledge at each end of the raphe (Figure 3a-d black arrow), or they may appear fused (Figure 3d white arrow), while internally two, only a single pore is observed (Figure 3e-g, j). Internally, the proximal raphe ends terminated in a broad, fused central helictoglossa (Figure 3e-f, h, white asterisk). The dorsal raphe ledge is nearly absent, especially through the valve center (Figure 3a-d). A reduced dorsal raphe ledge is present, more accentuated towards the distal end of the valve (Figure 3a-b, black asterisk). The dorsal and ventral striae are continuous through the valve center, slightly radiate (Figure 3a-d), and not resolved in the LM (Figure 2b). Figure 3e-j shows internal views of the deformed valves and other deformed structures, like the raphe, which is in a different position than in the undeformed valves.

We obtained 4,004 bp nucleotide sequences (SSU 1375 bp, rbcL 1444 bp, psbC 1185 bp; GenBank accession numbers: ON714546, ON736839, ON736840) for the CIBA 160 strain (H. adumbratoides) from the Pacific Ocean. Comparison of our sequences to those of the type species from the Atlantic Ocean in GenBank showed 100, 99.8, and 99.5% similarity for SSU, rbcL, and psbC, respectively. The BI and ML phylogenetic analyses placed the H. adumbratoides strains in one clade with H. pellicula as a sister clade (Figure 4). This node was supported strongly by the BI (100%) and ML (92%) analyses.

Accurate identification of a species depends, in principle, on the methods' reliability. Historically, and even today, the identification of a diatom species is based on morphometric aspects observed under light microscopy, which requires extensive taxonomic experience (^{Mora et al., 2019}). The characterization of certain diatom species is impossible only with this tool because of their small size and inconspicuous diagnostic structures (^{Li et al., 2018}; ^{D. Mann et al., 2020}). Fortunately, this issue can be resolved with electron microscopy. However, not all diatom species can be delineated using morphology, especially species with subtle morphological differences (^{Beszteri et al., 2007}; ^{Evans et al., 2007}; ^{Malviya et al., 2016}). To aid in determining species boundaries among diatoms, molecular tools, such as DNA sequences are applied (^{An et al., 2017}; ^{Beszteri et al., 2007}; ^{Evans et al., 2007}; ^{Guillard, 2005}; ^{D. Mann et al., 2010}, ²⁰²⁰; ^{Medlin, 1991}). However, this methodology has limitations as it may be unable to resolve the species identity (^{Malviya et al., 2016}) without conspecific and/or closely related species sequences in the nucleotide database. Therefore, morphological, and molecular methods are important in diatoms and should be considered as elements of a synergistic approach to species identification challenges.

• ^{Mora et al., 2019}
  Morphology and metabarcoding: a test with stream diatoms from Mexico highlights the complementarity of identification methods

  Freshwater Science, 2019
  Mora, D., Abarca, N., Proft, S., Grau, J., Enke, N., Jiménez, J., Skibbe, O., Jahn, R., & Zimmermann, J. (2019). Morphology and metabarcoding: a test with stream diatoms from Mexico highlights the complementarity of identification methods. Freshwater Science, 38, 448-464. https://doi.org/10.1086/704827
• ^{Li et al., 2018}
  The morphology and molecular phylogenetics of some marine diatom taxa within the Fragilariaceae, including twenty undescribed species and their relationship to Nanofrustulum, Opephora and Pseudostaurosira

  Phytotaxa, 2018
  Li, C. L., Witkowski, A., Ashworth, M., Dąbek, P., Sato, S., Zgłobicka, I., Witak, M., Khim, J. S., & Kwon, C. J. (2018). The morphology and molecular phylogenetics of some marine diatom taxa within the Fragilariaceae, including twenty undescribed species and their relationship to Nanofrustulum, Opephora and Pseudostaurosira. Phytotaxa, 355(1), 1-104. https://doi.org/10.11646/phytotaxa.355.1
• ^{D. Mann et al., 2020}
  Ripe for reassessment: A synthesis of available molecular data for the speciose diatom family Bacillariaceae

  Molecular Phylogenetics and Evolution, 2020
  Mann, D., Trobajo, R., Sato, S., Li, C., Witkowski, A., Rimet, F., Ashworth, M., Hollands, R., & Theriot, E. (2020). Ripe for reassessment: A synthesis of available molecular data for the speciose diatom family Bacillariaceae. Molecular Phylogenetics and Evolution, 158, 106985. https://doi.org/10.1016/j.ympev.2020.106985
• ^{Beszteri et al., 2007}
  An assessment of cryptic genetic diversity within the Cyclotella meneghiniana species complex (Bacillariophyta) based on nuclear and plastid genes, and amplified fragment length polymorphisms

  European Journal of Phycology, 2007
  Beszteri, B., John, U., & Medlin, L. K. (2007). An assessment of cryptic genetic diversity within the Cyclotella meneghiniana species complex (Bacillariophyta) based on nuclear and plastid genes, and amplified fragment length polymorphisms. European Journal of Phycology, 42(1), 47-60. https://doi.org/10.1080/09670260601044068
• ^{Evans et al., 2007}
  An Assessment of Potential Diatom “Barcode” Genes (cox1, rbcL, 18S and ITS rDNA) and their Effectiveness in Determining Relationships in Sellaphora (Bacillariophyta)

  Protist, 2007
  Evans, K., Wortley, A. H., & Mann, D. (2007). An Assessment of Potential Diatom “Barcode” Genes (cox1, rbcL, 18S and ITS rDNA) and their Effectiveness in Determining Relationships in Sellaphora (Bacillariophyta). Protist, 158, 349-364. https://doi.org/10.1016/j.protis.2007.04.001
• ^{Malviya et al., 2016}
  Insights into global diatom distribution and diversity in the world’s ocean

  Proceedings of the National Academy of Sciences of the United States of America, 2016
  Malviya, S., Scalco, E., Audic, S., Vincent, F., Veluchamy, A., Poulain, J., Wincker, P., Iudicone, D., De Vargas, C., Bittner, L., Zingone, A., & Bowler, C. (2016). Insights into global diatom distribution and diversity in the world’s ocean. Proceedings of the National Academy of Sciences of the United States of America, 113(11), E1516-E1525. https://doi.org/10.1073/PNAS.1509523113/DCSUPPLEMENTAL/PNAS.1509523113.SAPP.PDF
• ^{An et al., 2017}
  Identification of benthic diatoms isolated from the eastern tidal flats of the Yellow Sea: Comparison between morphological and molecular approaches

  PLoS ONE, 2017
  An, S. M., Choi, D. H., Lee, J. H., Lee, H., & Noh, J. H. (2017). Identification of benthic diatoms isolated from the eastern tidal flats of the Yellow Sea: Comparison between morphological and molecular approaches. PLoS ONE, 12(6). https://doi.org/10.1371/journal.pone.0179422
• ^{Beszteri et al., 2007}
  An assessment of cryptic genetic diversity within the Cyclotella meneghiniana species complex (Bacillariophyta) based on nuclear and plastid genes, and amplified fragment length polymorphisms

  European Journal of Phycology, 2007
  Beszteri, B., John, U., & Medlin, L. K. (2007). An assessment of cryptic genetic diversity within the Cyclotella meneghiniana species complex (Bacillariophyta) based on nuclear and plastid genes, and amplified fragment length polymorphisms. European Journal of Phycology, 42(1), 47-60. https://doi.org/10.1080/09670260601044068
• ^{Evans et al., 2007}
  An Assessment of Potential Diatom “Barcode” Genes (cox1, rbcL, 18S and ITS rDNA) and their Effectiveness in Determining Relationships in Sellaphora (Bacillariophyta)

  Protist, 2007
  Evans, K., Wortley, A. H., & Mann, D. (2007). An Assessment of Potential Diatom “Barcode” Genes (cox1, rbcL, 18S and ITS rDNA) and their Effectiveness in Determining Relationships in Sellaphora (Bacillariophyta). Protist, 158, 349-364. https://doi.org/10.1016/j.protis.2007.04.001
• ^{Guillard, 2005}
  Purification methods for microalgae

  Algal culturing techniques, 2005
  Guillard, R. R. L. (2005). Purification methods for microalgae. In R. A. Andersen (Ed.), Algal culturing techniques (pp. 117-132). Elsevier Academic Press. Phycological Society of America.
• ^{D. Mann et al., 2010}
  DNA barcoding for species identification and discovery in diatoms

  Cryptogamie Algologie, 2010
  Mann, D., Sato, S., Trobajo, R., Vanormelingen, P., & Souffreau, C. (2010). DNA barcoding for species identification and discovery in diatoms. Cryptogamie Algologie, 31, 557-577.
• ²⁰²⁰
  DNA barcoding for species identification and discovery in diatoms

  Cryptogamie Algologie, 2010
  Mann, D., Sato, S., Trobajo, R., Vanormelingen, P., & Souffreau, C. (2010). DNA barcoding for species identification and discovery in diatoms. Cryptogamie Algologie, 31, 557-577.
• ^{Medlin, 1991}
  Morphological and genetic variation within the diatom Skeletonema costatum (Bacillariophyta): evidence for a new species, Skeletonema pseudocostatum

  Journal of Phycology, 1991
  Medlin, L. K., Elwood, H. J., Stickel, S., & Sogin, M. L. (1991). Morphological and genetic variation within the diatom Skeletonema costatum (Bacillariophyta): evidence for a new species, Skeletonema pseudocostatum. Journal of Phycology, 27, 514-524.
• ^{Malviya et al., 2016}
  Insights into global diatom distribution and diversity in the world’s ocean

  Proceedings of the National Academy of Sciences of the United States of America, 2016
  Malviya, S., Scalco, E., Audic, S., Vincent, F., Veluchamy, A., Poulain, J., Wincker, P., Iudicone, D., De Vargas, C., Bittner, L., Zingone, A., & Bowler, C. (2016). Insights into global diatom distribution and diversity in the world’s ocean. Proceedings of the National Academy of Sciences of the United States of America, 113(11), E1516-E1525. https://doi.org/10.1073/PNAS.1509523113/DCSUPPLEMENTAL/PNAS.1509523113.SAPP.PDF

After a morphometric review of the images of the laboratory cultured cells of the CIBA 160 strain obtained with both light and electron microscopy, it was not possible to identify this strain with any previously described taxon. However, approximations were made with Amphora adumbrata and Halamphora adumbratoides. Nevertheless, the morphometric analyses did not allow the taxonomic determination of the CIBA 160 strain as H. adumbratoides because the morphology of this strain does not exactly match the original description reported by ^{Stepanek & Kociolek (2018)}, specifically due to the shape and size of the valve. In the original description of H. adumbratoides, the valves were narrow and semi-lanceolate, and the valve ends narrowly rounded to weakly subcapitate in larger specimens. The dorsal and ventral margins, however, do coincide with the original description, as they are arched and straight, respectively (Figure 3a-d). The presence of pores at the end of the dorsal raphe ledge at each end of the raphe was not mentioned in the original description. The axial area, not easily distinguishable in the original description, was not observed in the specimens of the CIBA 160 strain analyzed.

• ^{Stepanek & Kociolek (2018)}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.

For the length and width of the valves, ^{Stepanek & Kociolek (2018)} reported ranges of 8.0-10.0 and 1.5-2.5 μm, while the cells (N=24) of the CIBA 160 strain recorded valve lengths and widths of 4.1-6.6 and 1.6-2.4 μm. Only the length range differed, as it was much shorter than in the original description. The number of dorsal and ventral striae in the CIBA 160 strain almost coincided with the original description, with 56-57 dorsal striae and ca. 70 ventral striae in 10 μm in the original description, while the striae range in 10 μm for the CIBA 160 strain were 57-60 and 60-70 for the dorsal and ventral striae, respectively.

• ^{Stepanek & Kociolek (2018)}
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.

A possible explanation for the size differences and morphological changes could be the effect of laboratory culturing on the cells of CIBA 160. In diatoms ^{Rose & Cox (2013)}, ^{Petrova et al. (2020)} and ^{Mohamad et al. (2022)} have reported morphological changes in laboratory cultured cells. Diatoms tend to produce small-sized cells over time due to asexual reproduction (^{Mohamad et al., 2022}). This phenomenon has been demonstrated in 15 monoclonal pennate diatoms, but the width and number of striae did not differ from the original description (^{Mohamad et al., 2022}). Our results support the findings of ^{Mohamad et al. (2022)}, and their proposal that the number of striae could be a useful character for species discrimination.

• ^{Rose & Cox (2013)}
  Some diatom species do not show a gradual decrease in cell size as they reproduce

  Fundamental and Applied Limnology, 2013
  Rose, D., & Cox, E. J. (2013). Some diatom species do not show a gradual decrease in cell size as they reproduce. Fundamental and Applied Limnology, 182(2), 117-122. https://doi.org/10.1127/1863-9135/2013/0406
• ^{Petrova et al. (2020)}
  Changes in valve morphology of two pennate diatom species during long-term culture

  Acta Biologica Sibirica, 2020
  Petrova, D., Bedoshvili, Y., Zakharova, Y., Volokitina, N., Likhoshway, Y., & Grachev, M. (2020). Changes in valve morphology of two pennate diatom species during long-term culture. Acta Biologica Sibirica, 6, 669-678. https://doi.org/10.3897/abs.6.e57888
• ^{Mohamad et al. (2022)}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346
• ^{Mohamad et al., 2022}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346
• ^{Mohamad et al., 2022}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346
• ^{Mohamad et al. (2022)}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346

Our molecular analyses confirmed that the CIBA 160 strain belongs to H. adumbratoides by showing very high similarity to the sequences of this species from the Atlantic Ocean: 100, 99.8, and 99.5% similarity for SSU, rbcL, and psbC, respectively. The present study corroborates the results of ^{Mohamad et al. (2022)} that molecular data remain consistent irrespective of morphological changes in laboratory-cultured diatoms. Phylogenetic analyses of this study were also congruent with the relationship presented by ^{Stepanek & Kociolek (2019)} for the H. adumbratoides species, which is a sister group to H. pellicula.

• ^{Mohamad et al. (2022)}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346
• ^{Stepanek & Kociolek (2019)}
  Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution

  Journal of Phycology, 2019
  Stepanek, J. G., & Kociolek, J. P. (2019). Molecular phylogeny of the diatom genera Amphora and Halamphora (Bacillariophyta) with a focus on morphological and ecological evolution. Journal of Phycology, 55. https://doi.org/10.1111/jpy.12836

We have registered morphological abnormalities in the cells of CIBA 160. The helictoglossa (Figure 3h white asterisk) is displaced to the left side of the valve. In contrast, the dorsal raphe ledge is very short and located only to the right of the valve (white arrow) (Figure 3h). The exact opposite configuration is visible in Figure 3i (white arrow), where the structure is seen to the left of the valve. These abnormalities could be associated with long-term culture of cells in the laboratory (^{Estes & Dute, 1994}; ^{Falasco et al., 2009}; ^{Petrova et al., 2020}).

• ^{Estes & Dute, 1994}
  Valve abnormalities in diatom clones maintained in long-term culture

  Diatom Research, 1994
  Estes, A., & Dute, R. (1994). Valve abnormalities in diatom clones maintained in long-term culture. Diatom Research, 9, 249-58. https://doi.org/10.1080/0269249X.1994.9705305
• ^{Falasco et al., 2009}
  Morphological abnormalities of diatom silica walls in relation to heavy metal contamination and artificial growth conditions

  Water S.A, 2009
  Falasco, E., Bona, F., Ginepro, M., Hlubikova, D., Hoffmann, L., & Ector, L. (2009). Morphological abnormalities of diatom silica walls in relation to heavy metal contamination and artificial growth conditions. Water S.A, 35, 595-606. https://doi.org/10.4314/wsa.v35i5.49185
• ^{Petrova et al., 2020}
  Changes in valve morphology of two pennate diatom species during long-term culture

  Acta Biologica Sibirica, 2020
  Petrova, D., Bedoshvili, Y., Zakharova, Y., Volokitina, N., Likhoshway, Y., & Grachev, M. (2020). Changes in valve morphology of two pennate diatom species during long-term culture. Acta Biologica Sibirica, 6, 669-678. https://doi.org/10.3897/abs.6.e57888

In the genera Amphora and Halamphora, most taxonomic determinations and descriptions of new species are based on morphological analyses of specimens from natural populations (^{Levkov, 2009}; ^{Wachnicka & Gaiser, 2007}). However, laboratory-cultured cells were also used for integrative taxonomic studies, combining morphological and molecular data (^{López-Fuerte et al., 2020}; ^{Stepanek et al., 2013}, 2015a, 2015b, ²⁰¹⁸).

• ^{Levkov, 2009}
  Amphora sensu lato

  Diatoms of Europe: Diatoms of the Europe inland waters and comparable habitats, 2009
  Levkov, Z. (2009). Amphora sensu lato. In H. Lange-Bertalot (Ed.), Diatoms of Europe: Diatoms of the Europe inland waters and comparable habitats (p. 916). A.R.G. Gantner Verlag K. G.
• ^{Wachnicka & Gaiser, 2007}
  Characterization of Amphora and Seminavis from South Florida, USA

  Diatom Research, 2007
  Wachnicka, A., & Gaiser, E. (2007). Characterization of Amphora and Seminavis from South Florida, USA. Diatom Research, 22(2), 387-455. https://doi.org/10.1080/0269249X.2007.9705722
• ^{López-Fuerte et al., 2020}
  Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico

  Phytotaxa, 2020
  López-Fuerte, F. O., Sala, S. E., Lora-Vilchis, M. C., & Murugan, G. (2020). Halamphora siqueirosii (Bacillariophyta), a new diatom species isolated from a hypersaline evaporation pond in Baja California Peninsula, Mexico. Phytotaxa, 451(2), 132-144. https://doi.org/10.11646/phytotaxa.451.2.3
• ^{Stepanek et al., 2013}
  Several new species of Amphora and Halamphora from the western USA

  Diatom Research, 2013
  Stepanek, J. G., & Kociolek, J. P. (2013). Several new species of Amphora and Halamphora from the western USA. Diatom Research, 28(1), 61-76. https://doi.org/10.1080/0269249X.2012.735205
• ²⁰¹⁸
  Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species

  Bibliotheca Diatomologica, 2018
  Stepanek, J. G., & Kociolek, J. P. (2018). Amphora and Halamphora from coastal and inland waters of the United States and Japan, with the description of 33 new species. In Lange-Bertalot, H. & Kociolek, J. P. Bibliotheca Diatomologica, volume 66, Gebr. Borntraeger Verlagsbuchhandlung, 260 pp.

It is important to mention that regardless of the origin of diatoms (natural or cultivated), the morphological description of a species must be accurate and informative, based on as much information as possible. This is because diatoms may present morphological variations throughout their life history, whether in the natural or artificial environment (^{Rose & Cox, 2013}).

• ^{Rose & Cox, 2013}
  Some diatom species do not show a gradual decrease in cell size as they reproduce

  Fundamental and Applied Limnology, 2013
  Rose, D., & Cox, E. J. (2013). Some diatom species do not show a gradual decrease in cell size as they reproduce. Fundamental and Applied Limnology, 182(2), 117-122. https://doi.org/10.1127/1863-9135/2013/0406

In our study, using morphological and molecular data has resulted in the reliable taxonomic identification of the CIBA 160 strain. Our results support using an integrative approach for fine-grained integrative taxonomic studies and the importance of laboratory cultures in the diatom taxonomy (^{Mohamad et al., 2022}).

• ^{Mohamad et al., 2022}
  Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture

  Diatom Research, 2022
  Mohamad, H., Mora, D., Skibbe, O., Abarca, N., Deutschmeyer, V., Enke, N., Kusber, W., Zimmermann, J., & Jahn, R. (2022). Morphological variability and genetic marker stability of 16 monoclonal pennate diatom strains under medium-term culture. Diatom Research, 37, 307-328. https://doi.org/10.1080/0269249X.2022.2141346

The taxonomic identification of the CIBA 160 strain as H. adumbratoides was not possible based only on morphometric characteristics. This was due mainly to differences in the valve leaflet length and the presence of pores at the extremes of the valve on the raphe channel. Molecular analyses, however, allowed us to determine species identity with reference DNA sequences deposited in GenBank. Using DNA sequence data is important for cryptic, pseudo-cryptic diatom species and diatoms in general. Integrated approaches can play a vital role in discovering species with broad morphological variations.