(Figures 4, 11 F–G)
Eupomatus elegans Haswell, 1883: 633, pl. 12, Fig. 1. Type locality: Port Jackson, Australia.
Hydroides norvegica (not Gunnerus, 1768).— Berkeley & Berkeley 1941: 56 (Newport Bay, Southern California, from “piling”); Hartman 1961: 44 (Los Angeles harbor, Southern California, fouling on hulls of ships); Lakshmana Rao 1969: 5, pl. 2, Figs a–g (Visakhapatnam and Madras, India; harbours); Salazar-Vallejo & Londoño-Mesa 2004: 54 (Tropical Eastern Pacific, checklist).
Hydroides pacificus Hartman, 1969: 759 –760, Figs 1–5 (type locality: Velero IV, sta. 1454-42, from hull of ship; central and Southern California); Díaz-Castañeda 2000: 327 (Todos Santos Bay, Baja California, terracotta plates, 10 m).
Serpula verimicularis (not Linnaeus, 1767).— Lakshmana Rao 1969: 2 –3, pl. 1, Figs a–g (Visakhapatnam and Madras, India; harbours; auctore misspelling).
Hydroides elegans.— Zibrowius 1971: 721–725, Figs 56–64 (Oahu, Hawaii, Newport Bay and Los Angeles Harbor, California); Long 1974: 28 (Pearl Harbor, Oahu, Hawaii, 9 m, fouling, with little coverage on test panels); Bailey-Brock 1976: 77–78 (Oahu Island and Hawaii Island, reef flats, live substrata [chlorophyte Dictyosphaeria cavernosa], epifauna of mobile substrata [mollusks and crustaceans], boat harbors, lagoons, brackish waters and reef slope); Dueñas 1981: 100– 101, fig. 31A–G (Cartagena Bay, Colombia; on plastic ponds for shrimp culture); Bailey-Brock 1987: 420–421 (Hawaii); Zibrowius 1992: 91 (discussion about its origin); Carpizo-Ituarte & Hadfield 1998: 15, Fig. 2 (Pearl Harbor, Hawaii, stimulation of metamorphosis); Bastida-Zavala & ten Hove 2003: 86–87, Figs 11 A–S (California and Hawaii; 0–1 m); Rodríguez-Valencia 2004: 520 (Petacalco Bay, Guerrero); Okolodkov et al. 2007: 40 (cryptogenic in the Mexican Pacific); Bastida-Zavala 2008: 25–26, fig. 6H (California and Baja California Sur; 0–1 m; deeper records questionable); Bastida- Zavala 2009: 535, Figs 2 E, 5F (identification key for Tropical America); Díaz-Castañeda & Valenzuela-Solano 2009: 513 (Salsipuedes Bay, Baja California, near tuna sea-cages); ten Hove & Kupriyanova 2009: 53 (worldwide serpulid checklist); Tovar-Hernández et al. 2009b: 331, Figs 3 l, 8a-c (fouling in Mazatlán, Sinaloa); Tovar-Hernández et al. 2012: 16–17 (Guaymas, Sonora, and Topolobampo, Sinaloa); Bastida-Zavala et al. 2014: 326, Figs 19.1e –h (exotic in the Mexican Pacific); Tovar-Hernández et al. 2014: 390 (Marina Palmira, Topolobampo, Sinaloa; API and Marina Fonatur, Guaymas, Sonora; and API and Marina Palmira, La Paz, Baja California Sur); Villalobos-Guerrero et al. 2014: 107 (Sinaloa, checklist); Sun et al. 2015: 23–29, fig. 6a–b (Capital Territory, New South Wales, Northern Territory, Queensland, South Australia and Western Australia; intertidal to 20 m; in natural habitat as lagoons, also in fouling communities of fish farms, harbors and ship’s hulls).
Material examined. 3,545 specimens.
Baja California Sur: UANL 7875, 548 spec. (Marina Santa Rosalía, sta. 3: 27°20’24.5”N, 112°15’56.1”W, April 19, 2010, ARB & JAL); UANL 7876 (same, sta. 4: 27°20’23.9”N, 112°15’55.9”W, April 19, 2010, ARB & JAL); UANL 7877, 1,271 spec. (same, Sta. 1, 27°20’25.2”N, 112°15’56.1”W, March 31, 2011, coll. JAL & ARB); UANL 7878, 1,702 spec. (Puerto Escondido, sta. 1: 25°48’51.8”N, 111°18’41.2”W, sta. 2: 25°48’53.1”N, 111°18’40.5”W, April 2, 2011, coll. ARB & JAL); UANL 7879 (Marina Palmira, La Paz, 24°11’05.3”N, 110°18’12.8”W, April 3, 2011, coll. ARB & JAL).
Oaxaca: UMAR-Poly 765, 4 spec. (Salina Cruz, angler pier, main dock, sta. 4, 1 m, May 26, 2011, coll. SGM et al.); UMAR-Poly 766, 10 spec. (same, hull of the shrimp boat “Golfo Pérsico”, 1 m, May 26, 2011, coll. EVP): UMAR-POLY 767, 8 spec. (“sample 85”, Oaxaca, 0–6 m, September 15, 2004).
Habitat. Intertidal to subtidal (20 m, Sun et al. 2015); deeper records, 110– 1,200 m from California (LACM- AHF 1377, 2475, 2792, 2850), were regarded to be questionable by Bastida-Zavala (2008: 26). Most records of Hydroides elegans were as fouling on artificial substrates: hulls of ships, terracotta and PVC panels and harbor structures. In the Hawaiian Islands it was also found on reef flats, reef slope and on the native alga Dictyosphaeria cavernosa (Bailey-Brock 1976). In the material studied the specimens were associated only with anthropogenic substrates in marinas and ports from La Paz, Puerto Escondido and Santa Rosalía, Baja California Sur, and from Salina Cruz, Oaxaca. Fouling species.
Distribution. Worldwide in temperate and tropical regions. Mediterranean, North Sea, Gulf of Mexico to Brazil, South Africa, Persian Gulf, India, Australia, Micronesia; California (USA) to Oaxaca (México), Hawaii (Zibrowius 1971; Bastida-Zavala & ten Hove 2002; 2003; Sun et al. 2015).
Remarks. The confusion between Hydroides elegans and H. norvegica Gunnerus, 1768 was unraveled by Zibrowius (1971), mainly on the basis of the collar chaetae: in H. norvegica with 2–3 teeth, while they have many small teeth in H. elegans. Hydroides norvegica has a distribution limited to the boreal Atlantic and subtidal waters in the Mediterranean, while H. elegans has a worldwide distribution in temperate and tropical waters, mainly in harbors and marinas (Zibrowius 1971; ten Hove 1974; Zibrowius 1992; Kupriyanova & Jirkov 1997; Bastida- Zavala & ten Hove 2002; 2003; Moen 2006; Bastida-Zavala 2008; Ben-Eliahu & ten Hove 2011). Long (1974: 28) recorded both H. elegans and H. norvegica from Oahu, Hawaii; however, after the revision of Zibrowius (1971) it is uncertain if the specimens identified by Long as H. norvegica belong to H. elegans or a different taxon.
Zibrowius (1992) doubted if Hydroides elegans originated from Australia; however, Ben-Eliahu & ten Hove (2011) propose that its origin probably is Australia and Sun et al. (2015) suggest on biogeographical and ecological reasons that H. elegans is likely to be a native to Australia. Many historic and recent records of H. elegans come from ports and marinas, on anthropogenic substrates; however, in the Hawaiian Islands the species was found in both natural sites and in boat harbors (Long 1974; Bailey-Brock 1976); also, H. elegans was found in Australia both in natural sites (lagoons), as well as fouling of fish farms, harbors and ship’s hulls (Sun et al. 2015).
Hydroides elegans has been present in the Eastern Pacific for at least 86 years; its first record was Newport Bay, Southern California (Berkeley & Berkeley 1941, as Hydroides norvegica); Bastida-Zavala & ten Hove (2003) recorded specimens collected in 1929 from the fouling of a submarine (U.S. Narwhal, N-1) in the harbor of San Francisco. In the Tropical Eastern Pacific the species was recorded first by Bastida-Zavala (2008) with a sample of more than a thousand specimens encrusting (1991) a PVC plate in La Paz Bay, Baja California Sur; later, Tovar- Hernández et al. (2009b) recorded the species in the fouling of Mazatlán port, Sinaloa.
Hydroides elegans was selected as a model species for research in biofouling and testing marine coatings for a number of reasons: its high abundance and the fact that their calcareous tubes can create problems for vessels. Furthermore H. elegans is easy to reproduce in laboratory (Carpizo-Ituarte & Hadfield 1998; Nedved & Hadfield 2008), making it possible to experiment with different means to avoid their settlement, e.g. antifouling paints (Johnson & Gonzalez 2004; Johnson et al. 2006); and has been observed that the larvae settle in response to both natural biofilms, formed by marine bacteria, or to artificially induced surfaces by cations and other chemicals (Nedved & Hadfield 2008).