Hebella albida, Watson, Jeanette E., 2011

Watson, Jeanette E., 2011, New species, new records and redescriptions of Thecate hydroids (Cnidaria: Hydrozoa: Leptothecata) from Southern Australia, Zootaxa 3122, pp. 1-36 : 8-10

Hebella albida sp. nov.

Fig. 4 A–G

Material examined. Holotype, NMV F171357, colony on Aglaophenia divaricata colony, Port Phillip Heads, depth 20 m, coll: J. Watson, July, 1982; colony formalin preserved. Paratype, NMV F 171358, microslide, Popes Eye reef, southern Port Phillip, depth 6 m, coll: J. Watson, 01/01/2010.

Description. Hydrorhiza comprising a single stolon running up stem and along hydrocladia of hydroid host; stolons tubular, thin and wrinkled.

Hydrothecae given off singly at intervals along hydrorhiza, usually inclined forward towards distal end of host hydrocladium; pedicels variable in length, straight to slightly bent, corrugated, widening a little distally below hydrotheca. Hydrothecae narrowly to broadly conical, symmetrical to slightly asymmetrical (depending upon angle of view), walls smooth but sometimes indistinctly undulated proximally, perisarc thinning distally; an annular thickening around base of hydrotheca, usually thicker on side opposite hydrocladium of host, a thin transverse to concave diaphragm at thickening. Margin of hydrotheca circular, approximately transverse to hydrothecal axis, rim smooth, everted, not replicated, operculum a flat dome of tissue torn aside at eruption of hydranth. Column of hydranth long, hypostome annular, with 24–26 blunt tentacles.

Gonothecae arising from hydrorhiza, interspersed among hydrothecae, inverted conical, similar in shape to hydrotheca but considerably larger, pedicel thick, variable in length, straight to strongly curved, deeply corrugated, junction with body of gonotheca sometimes marked by a constriction in perisarc, walls of gonotheca often shallowly undulated proximally becoming smooth distally, margin truncate, transverse to axis, rim circular, weakly everted or smooth, aperture closed by a thin flattened dome of tissue torn away at emergence of first medusa; gonophore with up to 10 developing medusae.

Perisarc of hydrothecal and gonothecal pedicels thick, that of hydrotheca moderately thick.

Medusa at release in the laboratory c. 1 mm in diameter, exumbrella quadrate to sub-hemispherical, jelly moderately thick, with scattered nematocysts and four radial canals, four perradial tentacle bulbs, two opposite bulbs bearing two long tentacles of equal length, the other two bulbs with tentacle buds only. Tentacles smooth at origin, of same width as bulb, then becoming thinner and coiling into a tight spiral, long and thin when straight; manubrium short, widening from base, extending less than halfway down bell, mouth quadrate with four thick lips. At 24–48 hours after release the perradial bulbs are somewhat elongated and four small interradial bulbs have developed on margin; no ocelli visible and fewer nematocysts present on bell. Due to medusa mortality no further development was observed.

Cnidome comprising two sizes of nematocysts of one class:

i) microbasic mastigophores, capsule narrowly ovoid, 9–10 x 3–4 µm, in tentacles of hydranth and tentacles of medusa; very difficult to discharge.

ii) microbasic mastigophores, capsule ovoid, 18–20 x 7–8 µm, shaft 14–18 µm long, tubule ~ 300 µm long, on umbrella of medusa, readily discharged.

Colony and hydrorhiza white; hydranths sometimes pale pink. Medusa translucent white, base of tentacle bulbs dull yellow.

Hydrorhiza diameter 70–80

Hydrotheca

length of pedicel 224–700 width of pedicel 108–152 length, annular thickening to margin 840–1040 diameter at annular thickening 144–256 diameter at rim 660–880

Gonotheca

length, including pedicel 1920–2000 diameter of pedicel 104–120 diameter at margin 760–800

Remarks. In size, general morphology of the hydrotheca and gonotheca and in its obligate association with aglaopeniid hydroids, Hebella albida is similar to Hebella furax Millard, 1957 , known from South Africa and the Seychelles ( Millard 1957, 1975) and Papua New Guinea ( Boero et al. 1997). The South African H. furax is both epizooic and parasitic whereas only epizooic colonies have been reported from Papua New Guinea. Hebella albida differs from H. furax in i) the gonotheca of H. albida has no opercular flaps compared with the four flaps of H. furax , ii) the medusa of H. albida is much larger at release than that of H. furax , and iii) the newly released medusa of H. albida has two long tentacles and two rudimentary tentacles on each of the perradial tentacular bulbs but not longer and shorter tentacles in these positions as described by Boero et al. (1997) for H. furax .

H. albida is similar to Anthohebella parasitica ( Ciamician, 1880) reported from tropical and warm temperate Australian waters (see Watson 2000). However there are sufficient differences in both hydroid and medusa phases to consider H. albida a distinct species.

H. albida occurs only on large southern Australian aglaopheniid hydroids including Aglaophenia divaricata ( Busk, 1852) , Aglaophenia cystifera Bale, 1915 and Macrorhynchia whiteleggei ( Bale, 1888) .

Medusae survived for two days in the laboratory, swimming feebly, usually remaining on the bottom of the vessel with one tentacle partially extended and the other spirally retracted.

Etymology. The species is named for the distinctive white colonies contrasting with the darker colour of the hydroid host colonies.

Figures

FIGURE 4. Hebella albida sp. nov. A, B, hydrothecae. C, hydrotheca with dome-shaped operculum. D, gonotheca. E, 24 hour old medusa released in laboratory. F, microbasic mastigophore from umbrella of medusa. G, microbasic mastigophore from hydranth. Scale bar: A – D, 0.5 mm, E, 1 mm, F, G, 20 µm.