David Muirhead and I did a dive with three others at Rapid Bay jetty on 9th March 2018. Three of us dived whilst two women just snorkelled. It was a sunny day, and the sea was flat calm. The water was 21-22°C and the vis was fair. My bottom time was 85 minutes. There was plenty to see in the way of fish and invertebrates.
David later reported sighting the hydrozoan Olindias malayensis. Olindias malayensis are described at https://www.inaturalist.org/taxa/1110142-Olindias-malayensis, including this close-up photo: –
David posted details of his sighting on iNaturalist at https://www.inaturalist.org/observations/10163727 . According to the post, the hydroid was “Actively pulsating bell but static on benthos @ depth 6m”.
Claudia Mills, a research scientist at the University of Washington’s Friday Harbor Labs in the San Juan Islands, Washington, commented “Gonads run along entire radial canals. See this curated image on WoRMS of O. malayensis (at) http://www.marinespecies.org/aphia.php?p=image&tid=285108&pic=134061. (Olindias malayensis from mouth of Brunswick River, New South Wales, Australia – Author Riek, Denis.”
Further, “Your image here has that light red color (sic) at the base of “crowded, club-shaped gonads”. I don’t know anything about the variation in this species and can find little beyond its original description in the scientific literature. But Olindias malayensis would otherwise be tropical or subtropical so?? I’ve studied “jellies” for decades, especially hydromedusae, stauromedusae and ctenophores – mostly cold water, shallow and deep.”
David had suggested that it looked as if the hydroid had caught a small pipefish. He later added, “Further to my comment about it having caught a small pipefish, I am fairly sure that is a smaller adult Pugnose pipefish (Pugnaso curtirostris) but the image quality prevents my resubmitting it for that purpose:).”
The following taxonomic details for Olindias malayensis are listed at https://www.inaturalist.org/taxa/1110142-Olindias-malayensis : –
Cnidarians Phylum Cnidaria
Hydrozoans Class Hydrozoa
My thanks to David Muirhead for these details.