Halecium nanum Alder, 1859

Calder, Dale R., 2019, On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689 (1), pp. 1-141 : 68-69

Halecium nanum Alder, 1859

Fig. 19b

Halecium nanum Alder, 1859: 355 , pl. 14, figs. 1–4.— Leloup, 1935a: 8.— Shier, 1965: 47, pl. 26.

C. markii .— Wallace, 1909: 137 [incorrect subsequent spelling of Halecium marki Congdon, 1907 ].

Type locality. Atlantic Ocean: SW of the Azores, 34°48’N, 34°25’W, “…on Gulf-weed…” ( Alder 1859: 355).

Material examined. Sanibel Island, beach at Lighthouse Point, 26°27’00”N, 82°01’01”W, on detached Thalassia at water’s edge, 15 March 2018, 18° C, 34‰, one colony, 0.6 mm high, without gonophores, coll. D. Calder, ROMIZ B4378.

Remarks. Halecium nanum Alder, 1859 was originally described as an epizoite of gulfweed collected from a location SW of the Azores, in the Sargasso Sea. This epibenthic hydroid comprises part of a remarkable biota that rafts on pelagic Sargassum ( Timmermann 1932; Burkenroad, in Parr 1939; Morris & Mogelberg 1973; Calder 1995). As such, the species can be expected to occur wherever pelagic Sargassum is transported by warm ocean currents in the North Atlantic. Halecium nanum was not considered by Cornelius (1995a: 291) to be a normal part of the hydroid fauna of northwest Europe, but it has been reported from warmer waters in the eastern Atlantic and Mediterranean ( Medel & Vervoort 2000). Distribution records in the western North Atlantic currently extend from the middle-Atlantic states of the USA ( Fraser 1944) to the southern Caribbean Sea ( Leloup 1935a). It has also been reported from the Fernando de Noronha Archipelago, Brazil ( Amaral et al. 2009). As a hydroid harbouring symbiotic zooxanthellae, H. nanum is a species of shallow waters, having been reported from the sea surface to a depth of 48 m ( Fraser 1944). Fraser believed a collection of the species from 1544 ftm (2824 m) off the east coast of the United States was likely to have been taken from sunken Sargassum . The hydroid is brownish in colour when alive due to zooxanthellae in its tissues. The morphologically similar H. xanthellatum Galea 2013 also has algal symbionts, but it differs in cnidome, in gonothecal shape, and in having flared hydrothecal margins ( Galea 2013). Hydranths of specimens identified as H. nanum by Wedler (2017b) from the Colombia were unusual in being white in colour, with green algal symbionts in the coenosarc. Gonothecae of these hydroids were also atypical in morphology and the identification is considered questionable.

Bosc (1797) applied the binomen Hydra articulata to a hydroid found on gulfweed during a passage from Bordeaux, France, to Charleston, South Carolina, USA. The species has long been considered indeterminate (e.g., Bedot 1901). Of the hydroids now known to occur on pelagic Sargassum , however, it most closely resembles Halecium nanum , and H. articulata constitutes a nomenclatural threat to that well-known species name. I had earlier intended to seek suppression of the unfamiliar H. articulata and to ask for conservation of the better-known H. nanum (Calder 1990 [1991a]: 22). Under the current edition of the ICZN, that can be accomplished by applying provisions relating to Reversal of Precedence. In the interests of nomenclatural stability, therefore, the well-known name Halecium nanum Alder, 1859 is designated herein as valid and as a nomen protectum, while Hydra articulata Bosc, 1797 is relegated to a nomen oblitum following articles of the code (ICZN Art. 2.9.1.1). Reversal of Precedence can be applied in this case because the binomen Hydra articulata has been unused as a valid name in zoology after 1899, while Halecium nanum has appeared in more than 25 publications by numerous authors (>10) in the past 50 years (e.g., Morris & Mogelberg 1973; Cornelius & Garfath 1980; Boero 1981; Spracklin 1982; Calder 1986, 1990 [1991a], 1991b, c, 1993b, 1995; Boero & Fresi 1986; Cairns et al. 1991, 2002; Bouillon et al. 1995; Cornelius 1995a; Farnsworth & Ellison 1996; Medel & López-González 1996; Medel & Vervoort 2000; Schuchert 2005; Calder & Kirkendale 2005; Altuna 2007; Oliveira & Marques 2007; Galea 2008; Amaral et al. 2009; Gravili et al. 2015; Oliveira et al. 2016).

While the pelagic phaeophytes Sargassum natans and S. fluitans are important substrates for H. nanum , this species is a substrate generalist, occurring also on benthic algae, seagrasses, other hydroids, buoys, and even tarballs (see Reported Distribution below). Taxonomic accounts of this hydroid, including synonymy lists of the species, are given in works such as those of Calder (1990 [1991a]) and Medel & Vervoort (2000).

As noted in the synonymy list above, Wallace (1909) reported this hydroid from the Dry Tortugas simply as “ C. markii ”. He nevertheless clearly intended it for Halecium Oken, 1815 and H. marki Congdon, 1907 (= H nanum ).

Reported distribution. Gulf coast of Florida. Dry Tortugas ( Wallace 1909: 137, as C. markii ).—Dry Tortugas, on Sertularella ( Leloup 1935a: 9) .—Cape San Blas area, on Syringodium , Thalassia , and Sargassum ( Shier 1965: 99) .

Elsewhere in western North Atlantic. North Atlantic Ocean: off the Antilles, on Sargassum ( Jäderholm 1903: 267) .— Bermuda: on Sargassum and large hydroids ( Congdon 1907: 474, as Halecium marki ).— USA: North Carolina, seaward side of Bogue Bank, on floating Sargassum ( Fraser 1912b: 368) .— USA: North Carolina, dredged off Beaufort, on Pasythea quadridentata (= Pasya quadridentata ) ( Fraser 1912b: 368, as? Halecium repens ).— Mexico: NNE of Yucatan Peninsula, 22°47’N, 86°10’W, on Sargassum ( Stechow 1914: 135; 1919: 36).— Bermuda: on floating Sargassum + Cow Ground Flat, on Pennaria ( Bennitt 1922: 245) .—Sargasso Sea, on Sargassum ( Hentschel 1922: 4) .—Sargasso Sea: 33°19’N, 43°55’W, on Sargassum + 31°30’N, 76°00’W, on Sargassum + 24°26’N, 64°44’W, on Sargassum + 27°20’N, 61°10’W, on Sargassum ( Timmermann 1932: 298, 301).— USA: South Carolina, off Murrells Inlet, 33°30’N, 79°00’W, on Sargassum ( Timmermann 1932: 301) .— Bonaire: Kralendijk, Pasanggrahan, on algae + De Hoop, on algae + Plaja Oranje Pan, on algae + Zuidpunt, on algae ( Leloup 1935a: 8, 9).—Sargasso Sea: NNE of Bermuda, 35°07’N, 63°35’W, on Sargassum ( Leloup 1935a: 9) .—West Indies: between Trinidad and Grenada, on Sargassum ( Leloup 1935a: 9) .—Sargasso Sea: E of the Bahamas, 23°57’N, 67°45’W, on Sargassum + 27°13’N, 62°16’W, on Sargassum ( Leloup 1935b: 4, as Halecium nanum var. alta ).—Sargasso Sea: W of Bermuda, 32°07’N, 66°35’W, on Sargassum ( Leloup 1937: 96, as Halecium nanum var. alta ).—Atlantic Ocean: Gulf Stream, on pelagic Sargassum + Sargasso Sea, on pelagic Sargassum (Burkenroad, in Parr 1939: 24) .—Gulf Stream: 130- 167 miles (209–269 km) S of Nantucket, USA, on Sargassum ( Fraser 1943: 89) .—Atlantic Ocean: E of New Jersey, 38°59’N, 70°07’W, 1544 ftm (2824 m), likely on sunken Sargassum ( Fraser 1944: 200) .—Sargasso Sea: NE of the Bahamas, on Sargassum ( Fraser 1944: 200) .— Puerto Rico: off NE coast, 18°27’35”N, 65°33’55”W, 26 ftm (48 m) ( Fraser 1944: 200).—Atlantic Ocean: off the Antilles, on Sargassum ( Fraser 1944: 200) .— USA: Texas, Port Aransas, on Sargassum and tar ( Deevey 1950: 345).— USA: southern Florida, on buoys ( Deevey 1950: 345).— USA: Florida, Florida Current off Miami, on Sargassum ( Adams 1960: 81) .—Sargasso Sea + Gulf Stream, several stations between Florida and New Jersey, on Sargassum natans , S. fluitans III, S. fluitans X, S. polyceratium , S. filipendula ( Rackley 1974: 21) .— Belize: Carrie Bow Cay ( Spracklin 1982: 240, as Halecium namum (sic)).—Sargasso Sea: Hydrostation “S” off Bermuda, 31 °45’N, 64°10’W, on pelagic Sargassum ( Butler et al. 1983: 232) .— Bermuda: on Sargassum ( Calder 1986: 136) .— Bermuda: Whalebone Bay, on Sargassum and other algae + Flatts Inlet, on Thalassia + Natural Arches Beach, on Sargassum (Calder 1990 [1991a]: 20).— Belize: Twin Cays, on Thalassia , Sargassum , benthic algae ( Calder 1991b: 223; 1991c: 2068).— Bermuda: on Sargassum natans and S. fluitans ( Calder 1995: 540) .— Bonaire ( Bouillon et al. 1995: 46).— Trinidad ( Bouillon et al. 1995: 46).—Sargasso Sea ( Bouillon et al. 1995: 46).— Belize: Spruce Cay + WeeWee Cay + Peter Douglas Cay ( Farnsworth & Ellison 1996: 66).— Panama: Colón, Isla Margareta, Fort Randolph, shore, 09°23’15”N, 79°53’11”W, 0-1 m + Bocas del Toro area, Mangrove Inn, 09°19’52.6”N, 82°15’17.7”W, 2-3 m + Bocas del Toro area, Crawl Cay, 09°15.261’N, 82°07.787’W, 2-4 m ( Calder & Kirkendale 2005: 481).—French Lesser Antilles: Guadeloupe, Grande-Terre, E of Saint François, 16°15’18.00”N, 61°14’37.00”W, seagrass meadows, on Thalassia ( Galea 2008: 22, as Halecium cf. nanum ).— French Lesser Antilles: Les Saintes, Terre-de-Haut, Pain de Sucre, 15°51’45”N, 61°35’60”W, rocky shore, on algae ( Galea 2008: 22, as Halecium cf. nanum ).—(?) Colombia: Santa Marta + Isla Piedra Ahogada ( Wedler 2017b: 110, figs. 105A–C).— Cuba: Havana, coral reef system west of the city (Castellanos et al. 2018: Supplementary Table S2).—(?) Panama: Bocas del Toro area, near Bocatorito Bay ( Miglietta et al. 2018b: 108, as Halecium cf. nanum ).

Figures

FIGURE 19. a, Halecium lightbourni: part of hydrocaulus with hydrothecae, Fort Myers Beach, ROMIZ B4377. Scale equals 0.1 mm. b, Halecium nanum: stolon with hydrocaulus and two hydrothecae, Sanibel Island, ROMIZ B4378. Scale equals 0.05 mm. c, Halecium tenellum: part of colony with a hydrotheca, Southwest Florida Shelf, ROMIZ B4379. Scale equals 0.05 mm. d, Halecium tenellum: part of colony with renovated hydrothecae, Southwest Florida Shelf, ROMIZ B4379. Scale equals 0.2 mm. e, Halecium sp.: part of a branch with three hydrothecae, Sanibel Island, ROMIZ B4381. Scale equals 0.1 mm. f, Halecium sp.: part of a branch with a hydrotheca, Southwest Florida Shelf, ROMIZ B1594. Scale equals 0.1 mm. g, Nemalecium lighti: part of colony with five hydrothecae, Fort Myers Beach, ROMIZ B4419. Scale equals 0.2 mm. h, Nemalecium lighti: two internodes, with hydrothecae, Fort Myers Beach, ROMIZ B4419. Scale equals 0.1 mm. i, Thyroscyphus marginatus: part of colony with three hydrothecae, Sanibel Island, ROMIZ B4382. Scale equals 0.5 mm. j, Thyroscyphus marginatus: hydrotheca, Sanibel Island, ROMIZ B4382. Scale equals 0.2 mm. k, Thyroscyphus ramosus: part of colony with three hydrothecae, Sanibel Island, ROMIZ B4385. Scale equals 0.5 mm. l, Thyroscyphus ramosus: hydrotheca, Sanibel Island, ROMIZ B4385. Scale equals 0.2 mm.