Smirnov R.V., Zaitseva O.V.* 2026. Redescription of Polarsternium plumosum (Ivanov, 1957) comb.n. (Annelida: Siboglinidae), with a taxonomic key to the species of the genus // Invert. Zool. Vol.23. No.1: 61–80 [in English].
Laboratory of Evolutionary Morphology, Zoological Institute RAS, Universitetskaya Emb. 1, 199034 Saint Petersburg, Russia.
* corresponding author
Roman Smirnov: vsroman@inbox.ru; ORCID: https://orcid.org/0000-0001-6207-680X
Olga Zaitseva: olgavzaitseva@gmail.com; ORCID: https://orcid.org/0000-0002-1080-3478
doi: 10.15298/invertzool.23.1.04
ABSTRACT: Siboglinum plumosum Ivanov, 1957 was originally described from a single specimen, the holotype collected in the Sea of Okhotsk at a depth of 194 m. Since then, the species has been repeatedly reported from the same and adjacent regions at depths of 119–387 m, but no data on its morphological variability have been available. Moreover, published information suggests that the holotype is highly incomplete and the original description contains major gaps. In this study, both the holotype of S. plumosum and several specimens from material recently collected near the type locality in the Sea of Okhotsk have been examined. These specimens lack papillae in the anterior (metameric) region of the trunk, bearing instead two continuous epidermal-muscular ridges. Multicellular glands in each ridge are arranged in at least two rows, increasing to 4–5 rows in the anteriormost portion of the trunk. This combination of characters does not fit the generic diagnosis of Siboglinum, but fully conforms to the diagnostic characters of Polarsternium. Consequently, the new combination Polarsternium plumosum (Ivanov, 1957) is proposed, with a full redescription of the species and illustrations of its morphological characters. The diagnosis of the genus Polarsternium is emended, key characters of all known species of the genus are summarised in a table, and an identification key to these species is presented for the first time.
KEY WORDS: Pogonophora, morphology, systematics, identification key, Siboglinum, Sea of Okhotsk.