Holotype: NMV F171357, colony on Aglaophenia divaricata colony, depth 20 m. Port Phillip Heads, Victoria, Australia; colony formalin preserved.
Paratype: NMV F171358, microslide, Popes Eye reef, depth 6 m. Southern Port Phillip, Victoria, Australia.
The species is named for the distinctive white colonies contrasting with the darker colour of the hydroid host colonies.
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.
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.
Colour: Colony and hydrorhiza white; hydranths sometimes pale pink. Medusa translucent white, base of tentacle bulbs dull yellow.
Victoria, Australia.
Subtidal, on other hydroids, particularly aglaopheniid hydroids including Aglaophenia divaricata (Busk, 1852), Aglaophenia cystifera Bale, 1915 and Macrorhynchia whiteleggei (Bale, 1888).