Biofouling hydroids (Cnidaria: Hydrozoa) from a Tropical Eastern Pacific island, with remarks on their biogeography Author Calder, Dale R. Author Carlton, James T. Author Keith, Inti Author Ashton, Gail V. Author Larson, Kristen Author Ruiz, Gregory M. Author Herrera, Esteban Author Golfin, Geiner text Journal of Natural History 2022 2022-07-11 56 9 - 12 565 606 http://dx.doi.org/10.1080/00222933.2022.2068387 journal article 126956 10.1080/00222933.2022.2068387 5ca061c2-0cbb-4434-a28a-fc6c60e7ed7c 1464-5262 7012486 Halopteris alternata ( Nutting, 1900 ) ( Figure 7a, b ) Plumularia alternata Nutting, 1900: 62 , pl. 4, figs 1, 2. Type locality Commonwealth of the Bahamas : Barracuda Rocks ( Nutting 1900 , p. 62, as Plumularia alternata ). Material examined Chatham Bay , 5.55318 , −87.03996 , 1 colony fragment in poor condition, 2.5 mm high, without gonothecae, coll . G . Ashton , #240556 . – Chatham Bay , 5.55318 , −87.03996 , 3 colony fragments, to 9 mm high, without gonothecae, coll . G . Ashton , #179805 . – Chatham Bay , 5.55318 , −87.03996 , 7 colony fragments, to 8 mm high, without gonothecae, coll . I . Keith , #307699 . – Chatham Bay , 5.55318 , −87.03996 , 11 colony fragments, to 1.2 cm high, without gonothecae, coll . G . Ashton , #240555 . Remarks Hydroids from Cocos Island correspond with accounts of Halopteris alternata ( Nutting, 1900 ) , originally described from the Bahamas . The species is widespread in shallow waters of the warm western Atlantic Ocean ( Oliveira et al. 2016 ; Calder 2019), although it was long included in the synonymy of the predominantly European H. diaphana (Heller, 1868) . Schuchert (1997) distinguished the two on the basis of morphological characters, and their separation as distinct species has been confirmed by DNA barcoding ( Galea et al. 2018 ; Moura et al. 2018 ). Differences distinguishing H. alternata from related species of the genus Halopteris Allman, 1877 ) have been reviewed by Schuchert (1997) and Calder et al. (2019) . While separated geographically by a significant biogeographic barrier, hydroids identified as H . cf. alternata lineage 5 (one of five lineages recognised under the name) from both Atlantic and Pacific sides of Central America were found by Moura et al. (2019) to have corresponding 16S haplotypes. Occurrence of the species in the Tropical Eastern Pacific has thereby been confirmed. In concert with its introduced status on the Galapagos Islands ( Carlton et al. 2019 ), we recognised it here as introduced on Cocos Island. Halopteris alternata has been reported from the region by Fraser (1938a , as Plumularia alternata ) from Mexico (Revillagegedo Islands; east of islands off Navidad Head; Isabel Island), Ecuador ( Galápagos Islands ; Santa Elena Bay), Colombia (Port Utria) and Panama (Jicarita Island; Pacora Island); by Fraser (1938c , as P. alternata ) from Panama (Secas Islands) and Mexico (Isabel Island); by Moura et al. (2018) from Panama (Coiba); and by Calder et al. (2019 , 2021) from mainland Ecuador (Salinas) and the Galápagos Islands . Elsewhere in the Pacific it occurs in Hawaii ( Cooke 1977 , as H. diaphana ), including the Northwestern Hawaiian Islands ( Calder and Faucci 2021 ). As for Fraser’s reports of the species from the eastern Pacific, at least some appear to have been based on misidentifications ( Schuchert 1997 ). An illustration in Fraser (1938a , pl. 14, fig. 71b) shows a colony with cornucopia-shaped rather than spindle-shaped gonothecae as in H. alternata ; no indication was given of its collection location. Records from the Indian Ocean ( Jarvis 1922 , as P. alternata ; Gravely 1927 , as P . sp. nr. alternata ) need confirmation. The known range of H. alternata in the Tropical Eastern Pacific extends from Isabel Island, Mexico , southwards to Salinas, Ecuador ( Fraser 1938a , 1938c ; Calder et al. 2021). The species was found in four of the samples examined here from Cocos Island. All of the examined specimens were sterile. Reported distribution Cocos Island: first record. Elsewhere: Western Atlantic ( Oliveira et al. 2016 ; Calder 2019); eastern Atlantic ( Ansín Agís et al. 2001 ); eastern Pacific ( Calder et al. 2019 , 2021); central Pacific ( Cooke 1977 , as Halopteris diaphana ; Calder and Faucci 2021 ); possibly Indian Ocean ( Jarvis 1922 , as Plumularia alternata ; Gravely 1927 , as Plumularia sp. nr. alternata ).