Hebella dyssymetra Billard, 1933

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 : 14-15

Hebella dyssymetra Billard, 1933

( Figs 3 K, S, T; 4E)

Material examined. Stn. 7, 24.i.2012, 6– 8 m, M044: hydrothecae on stems of Ventromma halecioides (Alder, 1859) , some spreading on the substrate of the latter, a dead gorgonian.

Remarks. Boero et al. (1997) provide a description of this species and a list of synonyms. This material shows that the portion of colony creeping on the host's stems, Ventromma halecioides (Alder, 1859) , has conspicuously asymmetric hydrothecae, nearly adnate basally to their substrate ( Fig. 3 S), identical to those observed earlier by Calder (1991) in material from Bermuda. In addition, a portion of the same colony extends over the substrate of V. halecioides , a dead gorgonian, and has pedicellate, nearly radially symmetrical hydrothecae ( Fig. 3 T).

The cnidome of the hydroid is composed of four types of capsules (none seen discharged): 1) minute, eggshaped microbasic heteronemes, ca. 3.7×1.6 µm, occurring occasionally in the coenosarc; 2) fusiform microbasic mastigophores, ca. 6.6×2.1 µm, abundant in the tentacles, also present in the coenosarc; 3) ovoid capsules provided with a lateral "beak" at the insertion of the shaft, ca. 6.1×2.6 µm, sparsely found in the coenosarc; 4) elongateovoid capsules, (16.5–18.9)×(5.6–6.4) µm, exclusively occurring in the hydrorhiza.

Boero et al. (1997) reported on the presence of only two size classes of microbasic mastigophores in the hydroid of this species, of which one is illustrated in their Fig. 8F , and corresponds to type 2 described here. Since some nematocysts (types 1 and 3) occur rarely in the coenosarc, and type 4 is only present in the hydrorhiza, I assume that these authors overlooked them. However, they illustrated ( Fig. 8G, H ) two additional microbasic mastigophores of the medusoid, which correspond well to types 3 and 4 described above.

Geographical distribution. Circumglobal in tropical to temperate seas ( Calder 1991).

Figures

FIGURE 3. A, B: Clytia hemisphaerica (Linnaeus, 1767) ― hydro- (A) and gonotheca (B). C, D: Clytia noliformis (McCrady, 1859) ― hydro- (C) and gonotheca (D). E:? Gastroblasta sp. ― hydrotheca. F, G: Orthopyxis sargassicola (Nutting, 1915) ― hydro- (F) and gonotheca (G). H, I: Egmundella humilis Fraser, 1936 ― hydro- and nematothecae from samples M 231 (H) and M 007 (I). J – P: Relative sizes of the hydrothecae of the hebellids discussed in the text. J, Q, R: Anthohebella communis (Calder, 1991) ― hydrothecae (J, Q) and gonotheca with medusoid gonophore (R). K, S, T: Hebella dyssymetra Billard, 1933 ― hydrothecae. L, U – Y: Hebella scandens (Bale, 1888) ― hydrothecae (L, U); gonotheca seen laterally (V) and apically (X), showing the four-flapped operculum; gonophore (Y). M, Z: Hebella sp. 1 ― hydrotheca. N: Hebella sp. 2 ― hydrotheca. O: Hebella sp. 3 ― hydrotheca. P: Hebella sp. 4 ― hydrotheca. Scale bars: 200 µm (H, I, Z), 300 µm (A – E, S, T), 500 µm (Q, R, U – Y), 1 mm (F, G, J – P).

FIGURE 8. A – H: Halopteris tenella (Verrill, 1874) ― stem internodes and cladia (A – C); hydrothecate internodes of the stem (D); hydrotheca (E); stem ahydrothecate segments showing varied number of nematothecae (F); male (G) and female (H) gonothecae. I – N: Aglaophenia postdentata Billard, 1913 ― stem internodes in specimens from Martinique (I) and Guadeloupe (J); cormidia in specimens from Martinique (K) and Guadeloupe (L); corbula (M); internode of corbulacosta showing the shape of the nematothecae (N). Scale bars: 100 µm (N), 200 µm (I – L), 300 µm (D – H), 500 µm (A – C, M).