Heterocoryne caribbensis Wedler & Larson, 1986

Heterocoryne caribbensis Wedler & Larson, 1986: 75, figs. 2 a-e; pl. 1 figs. 4–6; Galea, 2013: 9, pl. 1, figs. G-I; fig. 2m; Maggioni et al. 2017: 737.

Examined material: Sample STE001, Sint Eustatius, 07/06/2015, polyps in ethanol. – Sample STE002, Sint Eustatius, 08/06/2015, polyps in ethanol. – Sample STE003, Sint Eustatius, 09/06/2015, polyps in ethanol. – Sample STE011, Sint Eustatius, 12/06/2015, polyps in ethanol and formalin. –Sample STE014, Sint Eustatius, 13/06/2015, polyps in ethanol and formalin. – Sample STE018, Sint Eustatius, 13/06/2015, polyps in ethanol. – Sample STE028, Sint Eustatius, 15/06/2015, polyps in ethanol and formalin. – Sample STE043, Sint Eustatius, 19/06/2015, polyps in ethanol and formalin. – Sample STE046, Sint Eustatius, 20/06/2015, polyps in ethanol. – Sample MHNG-INVE-0069670, Guadeloupe, 03/12/2009, polyps in ethanol.

Description: Polyp. Colonies monomorphic, living in association with sponges (figs. 6 A-C). Hydrorhiza tubular, branched, covered by perisarc and growing within sponge host. Pedicels unbranched, covered by a thin perisarc and by the sponge, the latter forming a cone-shaped cover around the base of the polyp (fig. 6C). Hydranth pyriform, up to 3.5 mm long, with variable diameter (160–630 Μm). Hypostome proboscis-like. One whorl of up to eight capitate tentacles below the hypostome and one whorl of up to 12 aboral capitate tentacles, each one provided with two or three partially-fused capitate tentacles on the proximal side (figs. 6D, E). Each tentacle with a terminal, nematocyst-rich capitulum (diameter: 95–130 Μm), with a central inclusion (lost in fixed material). Tentacles up to 1 mm long. One fixed gonophore (eumedusoid) per polyp, among oral tentacles. Living hydranths with white hypostome, and a reddish gastric cavity (figs. 6 A-C). Desmonemes, small and large stenoteles (fig. 6F) occurring in the capitula, and rarely scattered in the hydrorhiza and in the hydranth.

Polyp cnidome. i) Desmonemes (undischarged: 8–9 × 4–5 Μm; discharged capsule: 7 × 4–5 Μm). ii) Large stenoteles (undischarged: 16–19 × 11–13 Μm; discharged capsule: 13–16 × 10–11 Μm). iii) Small stenoteles (undischarged: 10–12 × 6–7 Μm; discharged capsule: 8–9 × 5 Μm).

Distribution: Presumably endemic to the Caribbean Sea (currently only known from Guadeloupe, Martinique, Puerto Rico, Sint Eustatius, US Virgin Islands).

Remarks: The analysed colonies fully agree with the specimens analysed by previous authors, both in general morphology and cnidome composition (Wedler & Larson, 1986; Galea, 2013). A minor difference is the presence, in some polyps, of four instead of three tentacles in the aboral whorl.