taxonID	type	description	language	source
1030B80D2E815D83B7015D44F12324A1.taxon	description	Fig. 2 A – D, G, H, Table 1	en	Ronowicz, Marta, Moreno, Bernabé, Szewel, Zuzanna, Więcławska, Julia, Brocławik, Olga, Mańko, Maciej Karol (2026): New invader in the Polish Baltic Sea Proper: phylogeny and global distribution of Calyptospadix cerulea Clarke, 1882 (Cnidaria, Hydrozoa). Aquatic Invasions 21 (2): 73-87, DOI: 10.3391/ai.2026.21.2.188183
1030B80D2E815D83B7015D44F12324A1.taxon	materials_examined	Material examined. Gulf of Gdansk, at Torpedo Station, 8 – 10 m, 23.11.2024, 8 ° C, infertile colonies, on the Torpedo Station wall, 17 – 48 mm high, coll. B. Moreno. Gulf of Gdansk, at Torpedo Station, 0 – 5 m, 22.12.2024, 6 ° C, infertile colonies, on Mytilus trossulus (A. A. Gould, 1850), Halichondria panicea (Pallas, 1766) and Amphibalanus improvisus (Darwin, 1854), 10 – 42 mm high, coll. B. Moreno. Gulf of Gdansk, Torpedo Station, 31.12.2024, 6 ° C, large infertile colony, 90 mm high, coll. B. Moreno.	en	Ronowicz, Marta, Moreno, Bernabé, Szewel, Zuzanna, Więcławska, Julia, Brocławik, Olga, Mańko, Maciej Karol (2026): New invader in the Polish Baltic Sea Proper: phylogeny and global distribution of Calyptospadix cerulea Clarke, 1882 (Cnidaria, Hydrozoa). Aquatic Invasions 21 (2): 73-87, DOI: 10.3391/ai.2026.21.2.188183
1030B80D2E815D83B7015D44F12324A1.taxon	description	Desciption. Colonies erect, reaching up to 9 cm in height, branched, bushy, covered by thick, brown perisarc (Fig. 2 A, B). Hydrorhiza composed of a dense network of anastomosing and intertwining fibers, forming a mat-like structure covering the substrate. Main stem monosiphonic, smooth, lacking nodes, sometimes covered by secondary tubes at the base. Branches positioned around the stem, originating with a ringed stretch of varying length. Secondary branches not common. Hydranths raise from short pedicels annulated basally, with conical hypostome and a single distal whorl of 8 to 11, filiform tentacles. Pseudohydrotheca covering polyp base but not reaching the base of tentacles (Fig. 2 H). In fully relaxed polyps, the pseudohydrotheca difficult to observe (Fig. 2 C). All examined colonies were sterile. Two types of nematocysts; larger oval microbasic euryteles with an average length of 8.1 μm and width of 4.9 μm, and smaller, round desmonemes with an average length of 3.7 μm and width of 3.3 μm. In the examined material, only eurytele capsules with a discharged cnidocil were observed (Fig. 2 G). Measurements of selected morphological characteristics are presented in Table 1.	en	Ronowicz, Marta, Moreno, Bernabé, Szewel, Zuzanna, Więcławska, Julia, Brocławik, Olga, Mańko, Maciej Karol (2026): New invader in the Polish Baltic Sea Proper: phylogeny and global distribution of Calyptospadix cerulea Clarke, 1882 (Cnidaria, Hydrozoa). Aquatic Invasions 21 (2): 73-87, DOI: 10.3391/ai.2026.21.2.188183
1030B80D2E815D83B7015D44F12324A1.taxon	discussion	Remarks. The presence of pseudohydrotheca and filiform tentacles clustered in a single whorl around the hypostome permit reliable distinction from another common athecate hydroid in the Baltic Sea, Cordylophora caspia (Vervoort 1964). The colonies of C. cerulea were numerous and occasionally reached high biomass and size at the sampling site (Fig. 2 A, B). They created bushy meadows both on the concrete walls and on biotic substrates such as bivalve shells of Mytilus trossulus, demosponge Halichondria panicea and cirriped Amphibalanus improvisus. The surface of colonies was covered with sediments and epibiota e. g., diatoms, protozoans, polyps of Aurelia aurita (Linnaeus, 1758) (Fig. 2 E) and M. trossulus juveniles. Direct spatial competition with the native hydroid Gonothyraea loveni was not observed; instead they grew on the substrate side by side, with occasional cases of G. loveni using C. cerulea as a substrate (Fig. 2 F). Hydranths were present in November despite the seawater temperature was 8 ° C, while regressed hydranths were observed in colonies collected in December, when temperature dropped to 6 ° C. However, when the latter were transferred to the laboratory and kept at 10 ° C, they had regrown actively functioning feeding polyps after few days.	en	Ronowicz, Marta, Moreno, Bernabé, Szewel, Zuzanna, Więcławska, Julia, Brocławik, Olga, Mańko, Maciej Karol (2026): New invader in the Polish Baltic Sea Proper: phylogeny and global distribution of Calyptospadix cerulea Clarke, 1882 (Cnidaria, Hydrozoa). Aquatic Invasions 21 (2): 73-87, DOI: 10.3391/ai.2026.21.2.188183
