Alekseev V.R., Chaban O.A., Sukhikh N.M. 2025. Morphological re-description of Eucyclops (Speratocyclops) speratus (Lilljeborg, 1901) (Copepoda: Cyclopoida) from the type locality, clarification of its diagnostic characters and distribution range // Arthropoda Selecta. Vol.34. No.4: 495–508 [in English].
Zoological Institute of the Russian Academy of Sciences, Universitetskaya emb., 1, St.-Petersburg 199034 Russia.
Victor Alekseev: alekseev@zin.ru; https://orcid.org/0000-0002-1968-2609
Olga Chaban: olga.chaban@zin.ru https://orcid.org/0009-0006-4136-8831
Natalia Sukhikh: nsukhikh@zin.ru https://orcid.org/0000-0002-8048-5241
doi:10.15298/arthsel.34.4.04
ABSTRACT. A detailed re-description of the external morphology of Eucyclops (Speratocyclops) speratus (Lilljeborg, 1901) females collected from Höje River near Lund, Sweden (the type locality), was conducted. Key characteristics of the type specimens were compared with those of several distant populations of the species across the Palearctic region. As a result, the newly described E. sibiricus Novikov et al., 2025 syn.n. was synonymized with E. (Sp.) speratus s.str. Distant populations of the same species from Sakhalin Island (Far East Russia) and Siberia appeared morphologically identical to specimens from Lund (Northern Europe) in all taxonomically significant macro- and micro-features. Molecular genetic differences observed for mitochondrial and nuclear genes among these distant populations suggest population polymorphism within the same widely distributed species. The modern natural range of E. (Sp.) speratus s.lat. is limited to the Palearctic region. An updated identification key for 10 taxa of the subgenus Eucyclops (Speratocyclops) is provided.
KEY WORDS: Eucyclops speratus, integrative taxonomy, cyclopid fauna, species delimitation, morhological variability, biodiversity, zoogeography, Palearctic, synonymy, identification key, Lund, Sweden.