Halecium dichotomum Allman, 1888

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 : 16-18

Halecium dichotomum Allman, 1888

( Fig. 4 K–Q)

Halecium dichotomum Allman, 1888: 13 , pl. 6.― Billard, 1910: 4.― Stechow, 1925:419.― Millard, 1957: 188; 1966: 466, fig. 10A–K; 1968: 256; 1975: 147, fig. 48A–G.― Migotto, 1996: 31, fig. 6F, G.

not Halecium cf. dichotomum ― Gili et al., 1989: 78, fig. 8.

Material examined. Stn. 2, 22.ii.2012, 1 m, M245: small female and male colonies on Sertularella diaphana (Allman, 1885) .

Remarks. No dichotomic arrangement of the lateral hydrophores, so characteristic of Allman's (1888) species, could be seen in this epizoic material with dwarfed, poorly developed colonies. However, the presence of both male and female gonothecae support this correct identification. The perisarc of gonothecae of both sexes has a filmy appearance and is easily collapsible, and wrinkled surfaces are less regularly marked than in earlier accounts ( Millard 1966, Migotto 1996), especially in males.

Two types of nematocysts occur in this species ( Fig. 3 Q): 1) microbasic mastigophores, ca. 5.9×1.6 µm, abundant in the tentacles, also scattered in the coenosarc; 2) larger and wider capsules with conspicuous shaft, (8.8–9.3)×(3.7–4.0) µm, occurring in the coenosarc. Since no discharged capsules of the latter type were found, I follow Migotto (1996) in considering them to be pseudostenoteles.

Geographical distribution. South Africa ( Allman 1888; Stechow 1925; Millard 1975), Brazil ( Migotto 1996), eastern Caribbean (present study).

Figures

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).

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).