On some tropical hydroids (Cnidaria: Hydrozoa), with descriptions of four new species Author Galea, Horia R. Hydrozoan Research Laboratory, 405 Chemin Les Gatiers, 83170 Tourves, France. Author Maggioni, Davide Università degli Studi di Milano-Bicocca, Dipartimento di Biotecnologie e Bioscienze, Piazza della Scienza 2, 20126 Milano, Italy. & Marine Research and Higher Education (MaRHE) Center, Università degli Studi di Milano-Bicocca, 12030 Faafu Magoodhoo, Maldives. text Zootaxa 2024 2024-03-20 5428 1 1 57 http://dx.doi.org/10.11646/zootaxa.5428.1.1 journal article 10.11646/zootaxa.5428.1.1 1175-5326 10842930 041905ED-FCED-4ED5-8248-E9AA8D6271E9 Anthoathecata : Aplanulata: Corymorphidae Three individual polyps of Corymorpha balssi Stechow, 1932 from the same crab host (designated as A, B and C in Fig. 23A ) were sequenced. The multi-locus (16S, 18S, and 28S rRNA) phylogenetic hypothesis ( Fig. 23A ) shows that all cluster together with maximal node supports (BPP = 1, MLBS = 100), and the species forms a sister-group relationship with a clade composed of C. bigelowi ( Maas, 1905 ) from Japan and C. tropica Galea, 2023 from Indonesia . Interestingly, the three polyps show a slight intra-specific genetic distance in the 16S rRNA region (0.7 ± 0.3%), suggesting that at least some of the polyps from the same host are not clonally-produced and may have settled independently on it. A phylogenetic hypothesis based on the COI gene was also produced to assess the phylogenetic affinities of the recently-described C. tropica , given the presence of multiple COI sequences in GenBank, and its sister-group relationship with C. bigelowi was confirmed ( Fig. 23B ). Notably, sequences obtained from Chinese samples identified as C. bigelowi and C. verrucosa ( Bouillon, 1978 ) , respectively, clustered together, showing minimal genetic distance (intra-group distance: 0.7 ± 0.2%), indicating that they likely belong to the same species, viz . C. verrucosa . As noted by Galea (2023: 457) , the present concept of C. bigelowi likely comprises a species complex. The Japanese material from which the sequences EU448099 (16S), EU272618 (18S), EU272563 (28 S) and JX121581 (COI), used to build the trees illustrated in Fig. 23 herein, bears the catalogue number KUNHM2829 of the Kansas University Biodiversity Institute and Natural History Museum, and is illustrated under that species in the World Hydrozoa Database.