Galea, Horia R., 2013, New additions to the shallow-water hydroids (Cnidaria: Hydrozoa) of the French Lesser Antilles: Martinique, Zootaxa 3686 (1), pp. 1-50: 5-6

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Hydractinia   sp.

(Pl. 1 C; Fig. 2 G, H)

Material examined. Stn. 6, 28.i.2012, 10– 18 m, M 104: fertile colony on limestone and sponge.

Description. Colony arising from creeping, ramified hydrorhiza devoid of spines. Three types of polyps: 1) gastrozooids, with 12–16 tentacles and the hypostome encircled by a conspicuous band of large heteronemes; 2) gonozooids, being smaller, modified gastrozooids, with 6–12 tentacles (though some individuals completely lack them), retaining the band of nematocysts around the hypostome; 3) tentaculozooids, rare and scattered within the colony. Gonophores medusoids, presumably male; rounded, with a central spadix and four radial canals; marginal bulbs and tentacles absent, velum not observed. Cnidome: 1) desmonemes, (6.9–7.2)×(3.7 –4.0) µm, abundant in the tentacles, also scattered in the coenosarc; 2) microbasic euryteles, (8.0– 8.5)×(2.9–3.2) µm, abundant in the tentacles, also scattered in the coenosarc, rare in the tentaculozooids; 3) microbasic heteronemes with short shaft, (9.8–10.4)×(4.2–4.5) µm, not uncommon in the coenosarc, more abundant in the tentaculozooids; 4) microbasic heretonemes with long shaft, (13.3–14.4)×(3.7 –4.0) µm, in a conspicuous band around the hypostome, also scattered in the coenosarc, abundant in both the tentaculozooids and the ectoderm of the gonophore; 5) ovoid capsules, (6.4–6.6)×(3.2–3.4) µm, of unidentified type (though not clearly visible, a shaft seems to be present), occurring exclusively, though rather scantly, in the tentaculozooids.

Remarks. The present material comes close to H. inermis (Allman, 1872)   , as described by Schuchert (2008), mainly due the presence of a conspicuous band of nematocysts around the hypostome, and the structure of the gonophore. However, the cnidome composition given by Boero (1981) for this species depicts small, ovoid atrichous isorhizas, not occurring in this material.

The finding of additional, fertile specimens of both sexes will allow for a more comprehensive description of the gonophores. In addition, the cnidome suggests that we are probably dealing with a new species.

Geographical distribution. Only known from Martinique.