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 Macrorhynchia philippina Kirchenpauer, 1872 ( Figure 7c ) Macrorhynchia philippina Kirchenpauer, 1872: 19 . Aglaophenia philippina Kirchenpauer, 1872: 45 , text-fig. p. 17; pl. 1, fig. 26; pl. 2, fig. 26a, b; pl. 7, fig. 26. Type locality Philippines : Manila ( Kirchenpauer 1872 ) . Material examined Chatham Bay, dock 004, no coordinates, 1 colony, 3 cm high, without reproductive structures, coll. G. Ashton, #266335. Remarks The reported geographic distribution of Macrorhynchia philippina Kirchenpauer, 1872 in the eastern Pacific Ocean extends from Gull Island, southern California , USA , and the Gulf of California , Mexico , to southern Ecuador ( Fraser 1947 , 1948 ). It has been widely reported within that range, with collections from Mexico (White Friars, Morro de Petatlán, Tenacatita Point, islands off Navidad Head, Ildefonso Island, Tres Marias Island, San Lorenzo Channel, Guaymas Bay), Costa Rica (South Viradores Islands), Panama (Bahia Honda, Secas Islands), Colombia (Gorgona Island, Port Utria), coastal Ecuador (Santa Elena Bay, La Plata Island, San Francisco Bay, La Libertad), and the offshore Galápagos Islands (Isabela, Española, Santa Cruz, San Cristóbal , Marchena, Santiago) ( Fraser 1938a , 1938b , 1938c , 1948 ; Calder et al. 2003 ). In the Galápagos, it is one of the most conspicuous hydroids in the upper 10 m on exposed coastal bottoms of the warmer eastern islands, usually occurring with Pennaria disticha Goldfuss, 1820 (D. Calder, personal observations, 16–22 June 2001 ). Its occurrence on Cocos Island thus coincides with the known distribution of the species across the Tropical Eastern Pacific Realm. Elsewhere, M. philippina is taken to be essentially circumglobal in shallow tropical to warm-temperate waters ( Moura et al. 2018 ; Calder and Faucci 2021 ). As with Halopteris alternata ( Nutting, 1900 ) , hydroids of the species from the western Atlantic and eastern Pacific have been shown to share the same 16S haplotypes ( Moura et al. 2019 ). Hydroids of M. philippina are venomous to humans ( Kirchenpauer 1872 , as Aglaophenia urens ; Gravely 1927 , as Lytocarpus philippinus ; Halstead 1988 , as L. philippinus ; Rifkin et al. 1993 , as L. philippinus ; Santhanam 2020 ). The absence of a planktonic stage that would permit natural long-distance transoceanic dispersal, combined with genetically identical populations in the Atlantic and Pacific, suggests that ship-mediated transport has likely played an important role in the distribution of this species. We regard it as likely native to either the Atlantic or Indo-West Pacific theatres, and introduced into the Tropical Eastern Pacific. Reported distribution Cocos Island: first record. Elsewhere: circumglobal in shallow tropical, subtropical, and warm-temperate seas ( Calder 1997 ; Ansín Agís et al. 2001 ; Schuchert 2003 ; Zhenzu et al. 2014 ; Moura et al. 2018 , 2019 ; Chakraborty and Raghunathan 2020 ; Calder and Faucci 2021 ).