Scientists from the Institute of Oceanography (Vietnam Academy of Science and Technology), together with scientists from Denmark and France, have clarified the taxonomic position of three species: Ceratocorys horrida (Stein 1883), C. gourretii (Schütt) Kofoid (1910), and C. armata (Paulsen 1931). These species existed for approximately 100 to over 140 years. All scientific literature on phytoplankton in coastal and open sea areas, from tropical to sub-temperate regions, confirms the distribution of these three distinct species, with C. horrida considered the type species as illustrated by Stein (1883). No type specimens of this species were sent to museums or contemporary laboratories.
All three species have a low upper carapace, with the arrangement of the carapace plates being completely identical (Figure 1-24). The lower carapace of C. horrida is box-shaped with 6 long or short spines (Figure 1-4); C. armata has a round cone shape with no or very short spines (Figure 5-8); and C. gourretii has a round tubular carapace with 5 spines that are shorter than those of the standard C. horrida (Figure 9-12).
Figure 1- 4, Ceratocorys horrida f. horrida; Figures 5 – 6, C. horrida f. armata; Figure 9 -12, C. horrida f. gourretii
Ceratocorys strains were isolated in the southern seas of France (Mediterranean Sea) and Nha Trang Bay (East Sea, Vietnam) and were cultured and maintained at the Phytoplankton Laboratory (Marine Botany Department, Institute of Oceanography), Concarneau and Roscoff Marine Biological Station (Brest, France). After a period of cultivation, the Ceratocorys horrida strain (VINNTB01-06) with many spineless cells took on the shape of C. armata. Previously, Graham (1942) also recorded this case in nature, but Carbonell-Moore (1996) considered this spineless form as a new species named Ceratocorys grahamii. Ceratocorys armata has strongly modified cell morphology characteristic of C. gourretii.
Figures 13-16, Ceratocorys bipes; Figures 17-20, C. magna; Figures 21-24, C. malayensis
Two species, Ceratocorys bipes (Figures 13-16) and C. magna (Figures 17-20), are large in size, have distinct shapes compared to other Ceratocorys species, and are rare in Vietnamese waters as well as worldwide. These are described in detail to provide a comprehensive overview of their morphological characteristics for dinoflagellate taxonomists. Ceratocorys malayensis (Figures 21-24), which is quite common in the South Central coastal region, is included in this description for its morphology and genetic characteristics.
Based on morphological analysis, all three Ceratocorys strains were analyzed for the 18S, 28S, ITS1-5.8S-ITS2 gene regions and the secondary structure of ITS2, demonstrating that the three species Ceratocorys horrida, C. armata, and C. gourretii are genetically identical and are all the same species. Based on the rules of the International Nomenclature for Botany, Schenzen code (2018), we constructed the following "formae":
- Ceratocorys horrida f. Horrida Stein 1883
- Ceratocorys horrida f. armata (Schütt) L. Nguyen-Ngoc, J. Larsen, KN Mertens, H. Doan-Nhu & N. Lundholm, comb. et stat. nov. 2025
- Ceratocorys horrida f. gourretii (Paulsen) L. Nguyen-Ngoc, J. Larsen, KN Mertens, H. Doan-Nhu & N. Lundholm, comb. et stat. nov. 2025
Figure 25, Secondary structure of ITS2; Figure 26, Phylogenetic analysis of the Protoceratiaceae family inferred from maximum likelihood, nearest neighbor joining, and Bayesian inference analyses based on an 881 bp alignment of the rDNA LSU region
This is one of the research papers on taxonomic science combined with genetic analysis to present the classification of new species for science, confused species, and their taxonomic position in the genetic phylogenetic tree, by a group of Vietnamese and international scientists, published in a specialized journal, the Journal of Phycology, a leading international journal specializing in research on all aspects of algae. The journal's first issue was published in March 1965 by the Phycological Society of America. To date, the journal has an IF=3.4, Hindex=180, and a Q1 ranking.
Further information about this article can be found at:
Nguyen-Ngoc, L., J. Larsen, H. Doan-Nhu, KN Mertenrs, N. Lundholm, … et al., 2025. Morphomolecular studies of Ceratocorys species (Dinophyceae, Gonyaulacales, Protoceratiaceae) reveal that Ceratocorys armata, C. gourretii and C. horrida are conspecific and should be considered formae of C. horrida. Journal of Physics. Published online on December 5, 2025. https://doi.org/10.1111/jpy.70108
