Nemalecium lighti ( Hargitt, 1924 )

Calder, Dale R., 2019, On a collection of hydroids (Cnidaria, Hydrozoa) from the southwest coast of Florida, USA, Zootaxa 4689 (1), pp. 1-141 : 72-74

Nemalecium lighti ( Hargitt, 1924)

Figs. 19g, h , 20

Halecium lighti Hargitt, 1924: 489 , pl. 4, fig. 13.

Type locality. Philippines: Oriental Mindoro, Puerto Galera ( Hargitt 1924: 489, as Port Galera Bay ) .

Material examined. Fort Myers Beach, 26°27’38.9”N, 81°57’58.4”W, on sponge, stranded on beach, 29° C, 33‰, 27 August 2018, several colony fragments, up to 8 mm high, without gonophores, coll. D. Calder, ROMIZ B4419.

Remarks. A brief history of the hydroid Nemalecium lighti ( Hargitt, 1924) , first described from the Philippines, has been given earlier ( Calder 1991b). Originally included in Halecium Oken, 1815 , the genus Nemalecium was established for the species by Bouillon (1986). The most distinctive generic character is the presence of nematodactyls, unique fingerlike defensive structures occurring within the tentacular whorl and curving over the hypostome of the hydranth. Curiously, hydroids of Nemalecium had seldom been reported anywhere in the world prior to the mid- 1980s. Records now suggest that they are both common and widespread, occurring in warm waters of the Atlantic, Pacific, and Indian oceans ( Calder et al. 2019). After having been recorded initially in the Atlantic Ocean from Bermuda ( Calder 1991b), they have been reported frequently in the Caribbean Sea (see records below), to the south in Brazil ( Oliveira et al. 2016), and recently from the Gulf of Mexico ( Mendoza-Becerril et al. 2018b). It is unclear whether N. lighti is a recent invasive species or one that had been widely overlooked or misidentified earlier.

Two species of Nemalecium have now been reported from the tropical western North Atlantic. Part of the material identified as N. lighti by Galea (2008) from the Caribbean Sea was referred by Galea et al. (2012) to a new species, N. gracile . Primary characters said by them to distinguish it from N. lighti include (1) hydranths that constantly forage and are long and nearly transparent, rather than ones that are nearly immobile, shorter, and milky white; (2) tentacles that are raised at different levels rather than being uniform in elevation; (3) internodes that are much more slender in form; (4) primary hydrophores that extend beyond the level of the distal internodes rather than terminating below them; (5) pseudostenoteles that are smaller (capsule length usually <30 μm rather than>30). As noted by Galea et al., hydroids assigned to N. lighti by Calder (1991b) from Bermuda resemble N. gracile and are likely referable to that species. The specific identity of specimens identified as N. lighti by Galea (2010: 4, 5), from Guadeloupe, is unclear. Swimming gonophores are produced by both species ( Galea et al. 2012).

The cnidome of N. cf. lighti includes several categories of nematocysts, including pseudostenoteles, microbasic mastigophores, microbasic euryteles, and rhopaloid heteronemes ( Galea et al. 2012). In material examined here from Florida, the nematocyst complement ( Fig. 20 ) included pseudostenoteles (31.2–34.8 μm long x 13.2–15.8 μm wide, undischarged, n=10, ROMIZ B4419), microbasic mastigophores (6.8–7.3 μm long x 1.8–2.1 μm wide, un- discharged, n=10, ROMIZ B4419), microbasic euryteles (7.6–8.8 μm long x 2.6–3.3 μm wide, undischarged, n=10, ROMIZ B4419), and rhopaloid heteronemes (3.8–6.0 μm long x 1.6–3.2 μm wide, undischarged, n=4, ROMIZ B4419). Pseudostenoteles of N. lighti are prominent on nematodactyls in the tentacular whorl of the hydranth. The species is known to be venomous to humans. The envenomations of a swimmer in Brazil, stung on the forearms, arms, neck, back, and later the thorax, were described by Marques et al. (2002).

While N. lighti has been classified as a haleciid based on colony morphology, molecular studies by Maronna et al. (2016) suggest that it is part of a different lineage. Their analysis indicated an affinity of the species with those of a new order group, Plumupheniida Maronna et al., 2016, but as a taxon incertae sedis within that group. More analyses to test that conclusion are warranted, and the species has been provisionally retained here in Haleciidae .

Reported distribution. Gulf coast of Florida. First record.

Elsewhere in western North Atlantic. Bermuda: Castle Harbour + Town Cut (Calder 1990 [1991a]: 27.— Belize: Twin Cays ( Calder 1991b: 223).— Panama: Colón, Fort Sherman dock, wood, 09°22’12”N, 79°56’59”W, 0–2 m + Colón, Fort Sherman dock, marina, 09°20’57”N, 79°54’10”W, 0–2 m + Portobelo Harbor, dock, 09°33’14”N, 79°39’34”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, Almirante pilings, 09°16.218’N, 82°23.382’W, 1–10 m + Bocas del Toro area, Hospital Point, 09°20”01.9”N, 82°13’07.7”W, 2–13 m + Bocas del Toro area, Cayo Solarte Sud, 09°18’45.3”N, 82°12’46.6”W, 2–3 m + Bocas del Toro area, Boca del Drago, 09°25’36.3”N, 82°19’30.1”W, 1–3 m + Bocas del Toro area, Cayos Zapotilla, 09°15.564’N, 82°02.750’W, 7–8 m + Bocas del Toro area, near Laguna Bocatorito, 2–4 m + Bocas del Toro area, Drago 2, mangroves, 1–2 m + Bocas del Toro area, Drago 2, 2– 4 m ( Calder & Kirkendale 2005: 483).—French Lesser Antilles: Les Saintes, Terre-de-Haut, Pompierre Bay, 15°52’25”N, 61°34’15”W, large rocks in seagrass meadows, on algae, concretions, sponge + Pain de Sucre, 15°51’45”N, 61°35’60”W, rocky shore, on sponge ( Galea 2008: 24; Galea et al. 2012: 47).— Cuba: Golfo de Batabanó, Punta Francés, Boya El Límite (Castellanos et al. 2009: 96, 2011: 15).—French Lesser Antilles: Martinique, Les Abîmes, 14.807514, -61.226698, 8 m, on dead gorgonians ( Galea et al. 2012: 48).—Caribbean Sea (Wedler 2017: 111).— Mexico: Alacranes Reef, on sponges, soft corals ( Mendoza-Becerril et al. 2018b: 130).— Cuba: Havana, coral reef system west of the city (Castellanos et al. 2018: Supplementary Table S2).— Panama: Bocas del Toro area, Smithsonian Tropical Research Station docks/ weather station + Isla San Cristóbal + vicinity of Manuguar Cay (Miglietta et al. 2018: 105, 106).

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.

FIGURE 20. Nemalecium lighti: nematocysts of hydranth, ROMIZ B4419. a, pseudostenotele. b, microbasic mastigophores. c, microbasic eurytele. d, rhopaloid heteronemes.