Halecium cymiforme Allman, 1888

Galea, Horia R., Häussermann, Verena & Försterra, Günter, 2009, New additions to the hydroids (Cnidaria: Hydrozoa) from the fjords region of southern Chile, Zootaxa 2019, pp. 1-28 : 5-6

Halecium cymiforme Allman, 1888

(fig. 2A–I)

Halecium cymiforme Allman, 1888: 15 , pl. 7 figs 1–5. – Hartlaub, 1905: 610, fig. H3.

not Halecium cymiforme – Stechow, 1913: 84, figs 50–53 (= Halecium cymosum Fraser, 1935 ).

Material examined. Stn. 9 – 24.02.2008, 20 m, A494 ( MHNG INVE 62834): a dense, fertile (female) colony, epizoic on dead gorgonian and bivalve shells attached to it.

Type locality. Puerto del Hambre (Port Famine), Strait of Magellan.

Description. Colony dense, bushy, without distinct primary axis, composed of numerous stems up to 3.5 cm high, arising from creeping hydrorhiza. Main stems, mostly monosiphonic, but some weakly polysiphonic basally (not shown). Branches arising at acute angles just below distal ends of stems, either singly or in (sub)opposite pairs. Higher order branches arising in similar manner from lower order ones. Both stem and branches slender, undivided (nodes absent), with nearly the same diameter throughout (100–125 µm). Perisarc rather thick and brown in basal part of colony, becoming thinner and more transparent distally; irregularly wrinkled, with occasional smooth stretches. Hydrothecae borne on distal ends of branches, on short primary hydrophores; hydrothecae deep (40–55 µm), with flared lateral walls and strongly everted margin; diameter 145–190 µm at rim, 90–115 µm at diaphragm; ring of desmocytes visible as refringent nodules above diaphragm; pseudodiaphragm absent. Hydrothecae with usually several renovations (generally 2 or 3); distal hydrophores of varied length. Hydranths badly preserved, tentacle number and dimensions could not be checked. Gonothecae arising either from within primary hydrothecae (fig. 2D) or at right angle from lateral branches, some distance below hydrothecal bases (fig. 2E). Examined colony monoecious, provided with numerous female gonothecae. Gonothecae 910–1070 µm long, 690–830 µm wide in frontal view; lenticular in shape, without protruding hydranths; borne on pedicels of variable length; aperture on distal end, rounded (145–170 µm wide), on shallow neck-like process with thickened perisarc; walls smooth to slightly undulated, perisarc rather thick. Mature gonothecae with inner, thin peridermal capsule enveloping about 12 eggs. Male gonothecae not observed. Nematocysts (undischarged): large capsules (microbasic heteronemes) (9.3–9.7) x (3.7–4.0) µm; small capsules (microbasic mastrigophores?) (5.7–5.8) x (1.6–1.7) µm.

Remarks. As noticed by Allman (1888), this peculiar species does not possess nodes dividing the stem and branches into internodes, and often two (sub)opposite branches are given off from below a hydrotheca.

A similar mode of branching is also found in several congeners, viz, H. cymosum Fraser, 1935 , H. curvicaule von Lorenz, 1886, H. dichotomum Allman, 1888 , H. expansum Trebilcock, 1928 , H. linkoi Antsulevich, 1980 , H. ovatum Totton, 1930 , H. pygmaeum Fraser, 1911 , H. scalariformis Billard, 1929 , H. tabulatum Watson, 2005 , and H. vagans Fraser, 1938 .

The female gonothecae of H. cymiforme very much resemble those of H. amphibolum Watson, 1993 , H. arcticum Ronowicz & Schuchert, 2007 , H. delicatulum Coughtrey, 1875 , and H. mediterraneum Weismann, 1883 .

A secondary, inner capsule, enveloping the female gonophore has also been reported in H. delicatulum , H. labrosum Alder, 1859 , and H. mediterraneum (see Schuchert 2005).

According to Totton (1930), H. cymiforme somewhat resembles his H. ovatum , but the latter is “more robust and of larger proportions”. Male and female gonothecae were likely present in the type material of Allman’s (1888) species, the latter ones measuring 1250 × 650 µm, with an aperture of 100 µm in diameter. Additionally, the diameters of both the stems (150–225 µm) and hydrothecal apertures (250–325 µm) are comparatively larger in H. ovatum .

Similar observations were made by Vervoort (1972a), who examined both the holotype and paratypes of H. ovatum . According to this author, both species exhibit the same mode of ramification, their gonothecae arise from the hydrothecal apertures, and the young male gonothecae are very similar in shape. Moreover, the maximal diameter of cauli in Totton’s species is ca. 300 µm, and that of the hydrothecae ca. 285 µm.

World distribution. Only known from southern Chile.

Records from Chile. Puerto del Hambre ( Allman 1888), South of Chiloé Island (present study).