Grebelnyi S.D. 2017. The significance of acontia for the traditional classification of Actiniaria. Conflict of morphological systematics and modern opinions based on the study of molecular markers // Invertebrate Zoology. Vol.14. No.2: 121–126 [in English].
Zoological Institute of Russian Academy of Sciences, Saint Petersburg, 199034, Russia. E-mail: email@example.com
ABSTRACT: In the order Actiniaria, one of the largest group of sea anemones Acontiaria was defined by Carlgren on the basis of the presence of special stinging organs — acontia. Inside it, the division into families was carried out according to a set of stinging capsules, which equip acontia. With the improvement of optical and electron microscopy, further study of stinging capsules led to a change in their formal classification, which violated the strictness of family diagnoses.
Nevertheless, this did not lead to an immediate restructure of the classification of acontiarian sea anemones, since other characters included by Carlgren in the diagnoses of the families were selected on the basis of a very thorough knowledge of the diversity of forms in this group and the deep intuition of this major specialist.
Published in recent years attempts to improve the system undertaken with the help of molecular-genetic methods, on the contrary, led to paradoxical results.
On the branches of phylogenetic trees, many closely related genera were isolated, and on schemes constructed using different markers (12S, 16S, 18S, 26S) they occupied very different positions. To clarify the reasons for the inconsistency of molecular data with traditional morphological classification, I conducted a pairwise comparison of the same sections of mtDNA. Pairwise comparison of the nucleotide sequences of mitochondrial genes showed the accumulation of multiple substitutions in some parts, indicative of a long independent evolution, and complete identity in other parts. These results, it seems to me, can be explained by the presence of recombination between the divergent regions of mtDNA and the unchanged regions, preserved in the nuclear genome of the cell in the form of numts — nuclear copies of mitochondrial DNA.
KEY WORDS: acontiarian sea anemone classification, 12S, 16S, 18S, 26S, mtDNA recombination.