Halecium lightbourni Calder 1990

Halecium lightbourni Calder, 1990 [1991a]

Fig. 19a

Halecium lightbourni Calder, 1990 [1991a]: 19, figs. 10, 11.

Type locality. Bermuda: Flatts Inlet, 0.5 m (Calder 1990 [1991a]: 19).

Material examined. Fort Myers Beach, on stranded Idiellana pristis, 01 March 2013, one colony, 3 mm high, without gonophores, coll. D. Calder, ROMIZ B4377.

Remarks. Halecium lightbourni Calder, 1990 [1991a] is an infrequently reported and poorly known species, originally described from Bermuda. It has subsequently been reported from Panama (Calder & Kirkendale 2005), Martinique (Galea & Ferry 2015), and Cuba (Castellanos et al. 2018) in the western North Atlantic, and from Brazil (Nogueira et al. 1997; Grohmann et al. 2003; Oliveira et al. 2016) in the western South Atlantic.

Hydroids of H. lightbourni resemble those of H. nanum Alder, 1859 in habit and in colony size (<1 cm high), but they differ most notably in lacking zooxanthellae. Among other characters differentiating H. lightbourni, colonies are less shrubby, hydrothecae tend to be narrower at the margin (129–160 μm vs. 147–182 μm), internodes of hydrocauli and branches are more slender at the nodes (65–86 μm vs. 84–89 μm), and large nematocysts (now considered pesudostenoteles rather than euryteles) are larger (8.3–8.9 μm long x 3.8–4.7 μm wide vs. 6.7–7.4 μm long x 3.1–3.8 μm wide) and somewhat different in shape (Calder 1990 [1991a]). The species has not been reported from pelagic Sargassum, a common substrate of H. nanum. The cnidome of H. lightbourni comprises microbasic mastigophores and small pseudostenoteles in addition to large pseudostenoteles (Calder 1990 [1991a]; Galea & Ferry 2015).

When originally described (Calder 1990 [1991a]), only trophosomes of H. lightbourni were available for study. Gonosomes were discovered and described in material from Martinique by Galea & Ferry (2015). From their account, female gonothecae are sac-shaped to reniform, with a lateral aperture for two gonothecal hydranths. They thus differ from those of H. nanum, which have a disto-lateral aperture at the end of two adnate, finely annulated tubes. Male gonothecae are clavate, as in many other species of the genus Halecium Oken, 1815. Gonothecae of the two sexes were found by Galea & Ferry on different colonies.

Reported distribution. Gulf coast of Florida. First record.

Elsewhere in western North Atlantic. Bermuda: Flatts Inlet, 0.5–1.0 m, on Pennaria disticha and algae + Harrington Sound, Cripplegate Cave, at entrance, 0.5 m, on Dynamena crisioides + Great Sound, on channel buoy, 2.5 m, on ascidians and Pennaria disticha (Calder 1990 [1991a]: 19).— Panama: Bocas del Toro, Boca del Drago, 0-3 m (Calder & Kirkendale 2005: 481).—French Lesser Antilles: Martinique, Saint Pierre, Tombant de la Galère, 14.75144, -61.18236, 10–15 m, on Thyroscyphus marginatus (Galea & Ferry 2015: 224).— Cuba: Havana, coral reef system west of the city (Castellanos et al. 2018: Supplementary Table S2).