Halecium discoidum, Galea, Horia R., 2013

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 : 18-20

Halecium discoidum sp. nov.

(Fig. 5A–E)

Material examined. Stn. 7, 24.i.2012, 6– 8 m, M036: fertile (female) colony on Thyroscyphus marginatus ( Allman, 1877) and its substrate, a sponge (holotype: MHNG-INVE-82923).

Description. Colony reptant, arising from creeping, branching, anastomozing hydrorhiza. Hydrocauli simple or occasionally branched, always monosiphonic, 0.5–1.6 mm high, widening gradually from base to tip, where they bear a terminal hydrotheca; perisarc thin, transparent and smooth throughout. Branches given off singly or in pairs from below stem hydrothecae; an internal perisarc plug at upper level of insertion of a branch on the stem ( Fig. 4A 1 , A4, A6), most probably as a result of mechanical strain. Hydrotheca 60–90 µm deep, flaring, margin everted; a basal diaphragm and a ring of desmocytes above; 280–355 µm wide at base, 440–515 µm wide at aperture; renovations present, lower order hydrophores of varied length, tapering gradually below, perisarc smooth. Female gonothecae borne on short (ca. 85 µm), conical pedicel given off from stolon; irregularly ovate, laterally flattened, 485–595 µm high, 530–585 µm wide in frontal view, perisarc smooth; aperture, a distal, circular notch, ca. 155 µm wide; ca. 8–10 oocytes per gonotheca, each 90–100 µm in diameter. Male gonothecae unknown. Nematocysts: 1) fusiform microbasic mastigophores ca. 5.9×1.9 µm, abundant in the tentacles, also scattered in the coenosarc; 2) rare microbasic heteronemes present in the coenosarc, with swollen capsules and a lateral "beak" at insertion of shaft, ca. 6.1×2.9 µm; 3) microbasic heteronemes with long, tubular, slender capsules, (6.7–7.7)×(2.1–2.4) µm, abundant in the coenosarc.

Remarks. A number of Halecium species have female gonothecae morphologically similar to those of Halecium discoidum sp. nov., but can be distinguished from it on the following accounts: 1) the Australian H. amphibolum Watson, 1993 has wrinkled internodes and the side branches arise some distance below the stem hydrothecae ( Watson 1993); 2) the Patagonian H. annuliforme Galea & Schories, 2012 has irregular, much longer, fully annulated internodes ( Galea & Schories 2012); 3) H. cymiforme Allman, 1888 , also from Patagonia, is more robust, with a peculiar mode of branching, and has the internodes mostly wrinkled throughout (Galea et al. 2009); 4) the northern H. labrosum Alder, 1859 forms large, polysiphonic colonies with irregular, smooth to corrugated internodes, and the hydrothecae are borne on hydrophores of varied length ( Schuchert 2005); 5) the mainly Mediterranean H. mediterraneum Weismann, 1883 has long, geniculate internodes, the hydrophores are well developed and have a conspicuous pseudodiaphragm on their adaxial side ( Schuchert 2005); 6) H. ochotense Linko, 1911 from the Okhotsk Sea is a large, polysiphonic species, with short, regular, slightly zigzagging internodes ( Naumov 1969).

Etymology. The specific name makes references to the disk-shaped female gonotheca.

Geographical distribution. Only known from Martinique.

FIGURE 5. A–E: Halecium discoidum sp. nov. ―various stems (A); hydranth protruding from its hydrotheca (B); female gonotheca with oocytes (C); female gonotheca in lateral (D1) and apical (D2) views; cnidome (E). F–I: Halecium xanthellatum sp. nov. ―three stems (F); female gonothecae (G), one of them showing a spent gonophore (G4); detail of the female gonotheca, showing the the twin hydrotheca in frontal (H1), lateral (H2), and apical (H3) views; cnidome (I). J–M: Halecium sp.―various stems (J), some bearing male gonothecae (J1–J3, J5); hydrophores and their corresponding hydrothecae (K, L); cnidome ( O). Scale bars: 10 µm (E, I, M); 100 µm (K, L), 200 µm (H), 300 µm (B), 500 µm (C, D, F, G, J), 1 mm (A).

Halecium xanthellatum sp. nov. (Fig. 5F–I)

Material examined. Stn. 16, 11.ii.2012, 10– 15 m, M167: small, fertile (female) colony on Sargassum sp. (holotype: MHNG-INVE-82924).

Description. Colony reptant, arising from creeping, branching, sometimes anastomozing hydrorhiza. Stems simple or occasionally branched, 340–900 µm high. Perisarc thin, transparent, wrinkled basally, fading out distally. Branches given off irregularly from below bases of stem hydrothecae. Hydrothecae borne distally on hydrantophores; walls divergent, rim flared (most obvious in young hydrothecae), a bit atrophied and not clearly everted in older ones; hydrotheca 30–35 µm high, 110–125 µm wide at base and 140–180 µm at aperture; renovations common, with lower order hydranthopores of varied length. Hydranths with 18–20 tentacles, the coenosarc crowded with zooxanthellae. Gonothecae, female in present material, arising from a short internodal apophysis lateral to a hydrotheca, or occasionally from within a theca; mitten-shaped, 720–790 µm long, 305–355 µm wide, tapering basally; in lateral view, distal part with a "bump" on one side, and the aperture on the opposite side; perisarc wrinkled on the bumped side, smooth on the other. Aperture borne on top of two appressed tubes, sunk for some distance inside the cavity of gonotheca, bearing distally a twin hydrotheca; the latter shaped, in frontal view, like the number 8, with two foramina visible below each hydrothecal base, allowing the passage of a pair of normally developed hydranths. The number of oocytes could not be ascertained properly, as most gonothecae have already expelled their eggs, while some others have the ectoderm of the blastostyle withdrawn, and retain a single, small oocyte. Male gonothecae unknown. Cnidome: 1) microbasic mastigophores, (6.4– 6.9)×1.9 µm, abundant in the tentacles, also scatterd in the coenosarc; 2) ovoid microbasic heteronemes, (3.5– 4.0)×(2.4–2.7) µm, not uncommon in the coenosarc; 3) pseudostenoteles, (9.9–10.2)×(4.8–5.1) µm, frequent in the coenosarc.

Remarks. This new species is reminiscent of H. nanum Alder, 1859 due to the presence of zooxanthellae in the coenosarc. However, unlike H. nanum , the hydrothecal margins are distinctly flared in H. xanthellatum . In addition, their gonothecae differ in shape, with those of H. nanum being more swollen and provided with fine annulations frontally, whereas those of H. xanthellatum are more slender and tubular, and bear coarse annulations exclusively on their dorsal side. Last but not least, the cnidome of H. nanum comprises, besides the common microbasic mastigophores, ovoid capsules identified by Calder (1991) as microbasic euryteles, while H. xanthellatum possesses rounded-ovoid microbasic heteronemes, as well as conspicuous pseudostenoteles.

The female gonothecae of the new species recall well those of the Arctic H. curvicaule von Lorenz, 1886, as illustrated by Marktanner-Turneretscher (1895, as H. kükenthali n.sp.) and Jäderholm (1909, equally as H. kükenthali ). However, this species may form large, polysiphonic colonies, with a peculiar mode of branching. Its hydrothecae have almost parallel, straight walls ( Schuchert 2001), and the coenosarc is devoid of zooxanthellae.

Equally similar in overall shape are the gonothecae of H. halecinum (Linnaeus, 1758) (see Schuchert 2005), H. inhacae Millard 1958 (see Millard 1975) and H. liouvillei Billard, 1934 (see Medel et al. 1998), but they have their apertures borne atop of somewhat raised collars and lack the "dorsal" annuli. Their respective trophosomes are also different, and no zooxanthellae are known to occur in their tissues.

Etymology. The specific name makes reference to the presence of numerous zoothanthellae in the coenosarc.

Geographical distribution. Only known from Martinique.

Figures

FIGURE 1. Map of Martinique [modified after Battistini (1978)] showing the location of hydroid sampling stations.

FIGURE 4. A: Hebella sp. 2 ― hydrothecae. B: Hebella sp. 3 ― hydrothecae. C: Hebella sp. 4 ― hydrothecae. D – J: Comparison of the cnidomes of Anthohebella communis (Calder, 1991) (D), Hebella dyssymetra Billard, 1933 (E), Hebella scandens (Bale, 1888) (F), Hebella sp. 1 (G), Hebella sp. 2 (H), Hebella sp. 3 (I), Hebella sp. 4 (J). K – Q: Halecium dichotomum Allman, 1888 ― various stems (K); male (L, M) and female (N, P) gonothecae; aperture of a female gonotheca in frontal view, showing twin hydrotheca (O); cnidome (Q). Scale bars: 10 µm (D – J, Q), 300 µm (K – P), 500 µm (C), 1 mm (A, B).