Hydrodendron

Galea, Horia R., 2010, Additional shallow-water thecate hydroids (Cnidaria: Hydrozoa) from Guadeloupe and Les Saintes, French Lesser Antilles, Zootaxa 2570, pp. 1-40 : 13

Hydrodendron sp.

(fig. 4A–D)

Material examined. Stn.9: 21.11.2009, 21 m—a few sterile stems, to 3 mm high, on basal part of stems of Thyroscyphus marginatus ( Allman, 1877) . Stn.10: 0 2.12.2009, 15–20 m—a few small, sterile colonies, with both stolonal and erect growth forms (to 2 mm high), on Halimeda sp. Stn.19: 26.11.2009, 6 m—minute sterile stems (1 mm high) and stolonal hydrothecae on Dictyota sp. and basal part of a stem of Macrorhynchia sp.

Description. Two growth forms: sessile hydrothecae and nematothecae arising from creeping stolon, and small erect stems. Erect form with minute, monosiphonic, unbranched, to 3 mm high stems; composed of a series of up to ten collinear to slightly zigzagging internodes. Nodes alternate, oblique, 40–65 µm wide. Internodes moderately long (185–260 µm), basal-most comparatively longer than following ones; each with bulges at both ends; a short (25–35 µm) apophysis borne on distal half of internode, supporting alternate hydrophores, and a nematotheca above axil formed by apophysis with stem. Hydrophores of variable length, funnel-shaped, carrying distally a hydrotheca (150–245 µm long, including hydrotheca); diaphragm not observed, rim even, margin flaring, 135–145 µm wide. Nematothecae tubular, 90–95 µm long, tapering below; margin slightly flaring, 50–55 µm wide (fig. 4C). Hydranths with ca. 14 tentacles, attached to internal wall of hydrotheca by mean of several desmocytes in an oblique row (fig. 4B). Nematophores long, slender, typical of the genus, with terminal capitation. Nematocysts (all seen undischarged): small, egg-shaped capsules (3.1–3.4 × 1.7–2.0 µm), in coenosarc; microbasic mastigophores (5.7–6.3 × 1.8–2.1 µm), in tentacles of hydranth and body of nematophores; slender, ovoid capsules of unidentified type (9.1–9.7 × 3.4–3.6 µm), in coenosarc; and large, swollen capsules of unidentified type (17.8–20.0 × 8.3–10.0 µm), between adjacent tentacles of hydranth, in nematophore capitations, and also in coenosarc. Gonothecae absent.

Remarks. The present material is unidentifiable in the absence of gonothecae. The nematothecae are characteristically situated above the axils formed by the stem apophyses and, in this respect, resemble those of H. dichotomum ( Allman, 1888) , H. leloupi Hirohito, 1983 , and H. sibogae ( Billard, 1929) . The finding of additional, fertile material would certainly allow a confident identification.