Hey. Sorry to leave you hanging.
Tentative ID is that this is plagiodinium. It is benthic, loves sand, photosynthetic, from the central america/gulf/carribbean area (but found all the way to Japan) and it shows up in the same samples as many of our favorites.
Others we've seen in the hobby highlighted in yellow.
here are some pics showing the same structure / shape as in your pics 3&4 in the first post and your video. Off-center lighter pigmented "cap" and a detectable groove running along the side. Laterally flattened, like most sand-dwelling species.
(plagiodinium belizeanum in center)
(scanning electron microscope of same species.)
Your video in
post #14 shows a copepod nauplius with one of these cells attached. The thrashing of the pod that fails to dislodge the cell shows how well the mucus of these benthic species works for attachment to sand etc.
Seeing that video and its other habits makes me think we should treat similar to prorocentrum. and a little more reading confirms that this dino is indeed a close relative of prorocentrum.
references:
Benthic dinos from meso-american reefs [pdf]
Ultrastructure of plagiodinium belizeanum
Now, for advice. Here's the best I've got.
Shoot for PO4 in the .05 to 0.10 range (depends on system - my tank dinos do poorly at 0.10), and NO3 detectable ~5ppm. Dose PO4, NO3 if needed, don't overfeed. Feed plain foods - cut out any aminos/coral snow etc.
Run UV into/out of display. 1 Watt per 2 to 3 gallons seems needed for these dinos. If this doesn't make a dent, then you can do a short blackout of ~48hr or so to force whatever cells are capable to go into the water and hit UV.
In the meantime, to try to protect some corals, hang filter floss in light and high flow - in front of powerhead. Some dinos will cling to these high flow places and turn the filter floss brown over the course of a day. Rinse out during the lights on period to wash away the dinos. (can wring out into a beaker - be careful of toxins - and check under 'scope to see what collected).
Blow off any brown that attaches to corals. Coral colonies go down fast when dinos attach. Siphon/export as much as you can, skim lots, harvest from ATS. Run GAC for toxins. since you are dealing with sandbed dinos, dosing Si may possibly help diatoms compete in the sand at the locations where the dinos are thriving.
Since you are reading through the main dino thread, assume stuff about prorocentrum is talking about your kind.
Any idea where you might have bought rock/algae/livestock that might have introduced this? curious whether it's a one-off mariculture shipment, a LFS, or an online retailer. Trying to figure if we should expect to see more of these in the hobby now.
hope some of it helps.
edit: dino-x isn't a dino treatment. It's same chemicals as algae-x and is a harsh algacide with a high frequency of reports of livestock loss, and a low frequency of reported success.
