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: 20-21

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Halecium   sp.

(Fig. 5 J–M)

Material examined. Stn. 16, 11.ii.2012, 10– 15 m, M 167: small, fertile (male) colony on Sargassum   sp.

Description. Stems up to 5 mm high arising from creeping, branching hydrorhiza. Basal part above origin from stolon short, either smooth or wrinkled. Remainder of stem divided into internodes by means of transverse to slightly oblique nodes, 65–70 µm wide; perisarc thin and smooth. Each internode 545–690 µm long, with a basal bulge above the proximal node, a terminal hydrotheca, and a latero-distal apophysis supporting the following internode. Branching occasional, with side branches given off laterally through a second distal stem apophysis, the hydrotheca thus becoming axillar; branches short, generally composed of a single hydranthopore. Hydrotheca shallow, ca. 25 µm deep, 120–130 µm wide at diaphragm and 135–150 µm at aperture; walls somewhat flaring, rim not everted; a row of desmocytes above the diaphragm; renovations not seen. Hydranths with 19–21 tentacles. Gonothecae, male in the present material, club shaped, 610–790 µm long, 185–250 µm wide, tapering abruptly proximally into indistinct pedicel, rounded distally. Cnidome: 1) microbasic mastigophores, (6.4–6.6)× 1.9 µm, abundant in the tentacles, also scattered in the coenosarc; 2) microbasic heteronemes, slightly wider than the mastigophores, ca. 6.6 × 2.4 µm, rare in the coenosarc; 3) pseudostenoteles, (10.3–11.6)×(4.8–6.1) µm, common in the coenosarc.

Remarks. This specimen comes close to H. lightbourni Calder, 1991   with respect to the shape and size of both internodes and hydrotheca. However, a difference in the cnidome composition prevents identification as this species: the small microbasic eurytele illustrated by Calder in his Fig. 11 A looks distinct from the microbasic heteronemes occurring in this material. In addition, I think that what Calder identified as large microbasic euryteles are instead pseudostenoteles. Indeed, the same capsules occur in specimens of H. dichotomum Allman, 1888   examined here and, though no discharged nematocysts could be found, I follow Migotto (1996), who indicated that they are pseudostenoteles.

Geographical distribution. Only known from Martinique.