Polunina Yu.Yu.1*, Drapun I.Eu.1, Kazakova D.M.1,3, Gubanova A.D.2*, Krivenko O.V.2, Kuleshova O.N.2, Baiandina Iu.S.2 2025. Pseudocalanus species (Calanoida: Clausocalanidae) in the Baltic and Black Seas: morphological and genetic differences // Arthropoda Selecta. Vol.34. No.3: 347–358 [in English].
1 Shirshov Institute of Oceanology, Russian Academy of Sciences, Nakhimovsky ave. 36, Moscow 117997 Russia.
2 Kovalevsky Institute of Biology of the Southern Seas, Russian Academy of Sciences, Nakhimov ave. 2, Sevastopol 299011 Russia.
3 Immanuel Kant Baltic Federal University, A. Nevsky str. 14, Kaliningrad 236041 Russia.
* Corresponding co-authors
Yulia Polunina: jul_polunina@mail.ru ORCID https://orcid.org/0000-0002-8157-9522
Inna Drapun innadra@gmail.com ORCID https://orcid.org/0000-0002-3217-8554
Diana Kazakova ximichesky@gmail.com ORCID https://orcid.org/0009-0009-7505-3506
Alexandra Gubanova: adgubanova@ibss-ras.ru ORCID https://orcid.org/0000-0002-1018-4662
Olga Krivenko olkrivenko@gmail.com ORCID https://orcid.org/0000-0001-6292-5293
Olga Kuleshova v_olgo4ka@inbox.ru ORCID https://orcid.org/0000-0003-3745-7066
Iuliia Baiandina sepulturka@mail.ru ORCID https://orcid.org/0000-0002-0866-6785
doi:10.15298/arthsel.34.3.06
ABSTRACT. A comparison of morphological and genetic variation between Pseudocalanus acuspes (Giesbrecht, 1881) from the Baltic and Pseudocalanus elongatus (Brady, 1865) from the Black Seas was conducted to find specific visible characteristics that could be used for their taxonomic identification in routine zooplankton studies. We made drawings of 72 females of Pseudocalanus, randomly selected from fixed zooplankton samples collected in waters of the southeastern Baltic Sea and the northwestern Black Sea, to measure their bodies in detail. We revealed that P. acuspes is distinguished by a rounder anterior cephalosome in a lateral view, shorter antennae (A1L), and a shorter prosome (PrL) as well as a larger genital segment (GL) of urosome (UrL). Several statistically significant differences were found in morphometric ratios between the body measurements of P. acuspes from the Baltic Sea and P. elongatus from the Black Sea. Specifically, for P. acuspes, the ratios are PrL/UrL < 2.2, A1L/L (%) < 87; GL/PrL > 16.8. For P. elongatus, these ratios are PrL/UrL > 2.2; A1L/L (%) > 92; GL/PrL < 16.5. The species identity of Pseudocalanus was confirmed using partial COI mtDNA gene analysis. Both regional populations form well-supported subgroups within species clusters on the COI phylogenetic tree. Individuals of P. elongatus from the Black Sea differ from all other haplotypes of this species, and no other geographically distinct sub-groups have been identified within the clade of P. elongatus. The P. acuspes cluster also consists of two well-supported subclusters, with Baltic Sea samples grouped with those from Balsfjorden (Norwegian Sea). Thus, the studied populations of both Pseudocalanus species are genetically distinct from those living in other parts of their geographical range. Therefore, morphological differences noted above need to be confirmed through additional investigations of these species from different parts of the range.
KEY WORDS: Pseudocalanus acuspes, Pseudocalanus elongatus, morphological and molecular genetic study, comparison of species, southeastern Baltic Sea, northern Black Sea.
