On 25th April 2011 we were diving "City Extra" as the 3rd dive of the day. "City Extra" is in front of a fairly popular seafood restaurant (of the same name) that is just out of Manado. It is a dive site that is mainly sandy bottom with patches of reef and a lot of "interesting critters", a sort of a muck dive. I have had fantastic dives there, both day and night, on every trip since 2002. Always interesting.....but this dive provided a mystery that took me years to resolve.
Photo taken 2nd July 2012 - 14 months after the original sighting
The description in my log book that day was ....." came across a transparent, gooey, jelly grey brown invertebrate with fine brown blotches and a thin white border with white spots at the back edge. Could be a worm but had two bumps or mounds toward the front from which 2 tentacle threads emerged and which were observed to move out over the rubble to about 100mm. When the tentacle encountered food, it grabbed it and the retracted back into one of its "mounds". Really weird and I have not been able to identify (perhaps ..brown, two headed, tentacled, snot worm)".
As I didn't have a camera, my log book in April 2011, I included this rough sketch.
My not very good sketch in July 2011.
I was so interested in this strange creature, I decided to get my old Nikonos V serviced (yep, was still using film in 2011) and try to find and photograph the creature next trip. So on that next trip, on 28th July 2011, I was armed with the Nikonos V, SB 105 strobe, 1:2 extension tube with ISO 50 Fujichrome......and no creature.
On the following trip to Nth Sulawesi, the quest was on. On 2nd July 2012, this time fully rigged with Nikon DSLR, I was back at "City Extra" and this time... there it was.
The one thing that I noticed this time, when observing it through the magnification of a viewfinder, was that what I thought previously were single tentacles were actually very complex branched tentacles. This time I was able to get the photos I was after.......but what was it ?
Only recently have I been able to learn what this strange creature is. What I have learned has made it even more interesting and something that I want to find and really observe again.
Thanks to Colleen at the Queensland Museum Discovery Centre and Dr John Healey and Kieran Aland at Queensland Museum for determining that this strange creature is the benthic Ctenophore ....Coeloplana....a name which is which is much better than my original descriptive name in 2011.
The platyctene Ctenophore .....Coeloplana sp.
So what is it...
Ctenophores are the comb jellies. Most comb jellies are pelagic, swimming and drifting with plankton in open ocean currents, directing their movements using bands of beating cilia, and armed with branched tentacles for entangling prey which they then retract into their body.
However a very small group of Ctenophores moved to live sedentary lives on the ocean floor (thats the "benthic" bit). These are the Platyctenida and they have flattened oval, bilaterally symmetrical bodies and look very much like flatworms, or plurobranchs, or nudibranchs, which they are often mistaken for.
They are found on rubble (like the one I found), rocks, soft corals, algae and on the bodies of other invertebrates.
The animal has two mounds which contain the sacs from which they eject or retract their tentacles. As you can see in the photographs, their feeding tentacles are branched and are also reported to be stinging and sticky in order to trap and immobilise their food.
Its recorded that they freely let the current carry their tentacles to feed, however the ones I observed on the sand & rubble bottom of "City Extra" appeared to have some sort of control over the direction and movement of the tentacles as they seemed to direct them to slowly meander over the top of the rubble and around small pieces of broken coral etc....until they caught something and retracted. Something to watch closer next time, current or some control.
The first one I saw in 2011 was about 25-30mm diameter, the second one in 2012 only about 20mm. I have not seen another since. These small creatures are cryptically coloured and, though the photographs (with strobes) show the animal fairly clearly, when in ambient light they are difficult to see and look very much like my initial name for them.
They must not have been identified by divers all that often because there do not seem to be many common names linked to those photos and descriptions that I am now able to search (now that I know what it is). The information available on particular species and their specific habits seems a bit limited - certainly there is a lot less than there is for nudibranchs and flatworms - so I expect that there is a large opportunity for new observation and knowledge.
Check out some websites (including Dr Bill Rudman's Sea Slug Forum - www.seaslugforum.net) and its links and you will be able to piece together some more information. This information will provide an idea of the range of habitat and the associated colours that hopefully will assist your search.
For me, I am going to ensure that I look hard for these amazing and interesting creatures across a range of habitats and really take the time to observe and record what they are doing.
Unfortunately "City Extra" is potentially going to become a victim of "land reclamation". This fantastic dive site located just off the coast down from Manado, provides an amazing range of life - from sea spiders that are indistinguishable from the sand and rubble, mimic octopus, nudibranchs, mandarin fish, ghost pipe fish, raggy scorpion fish, egg laying squid, pigmy seahorses and a heap of weird critters that extends through to the occasional dugong feeding on the patches of sea grasses. A magic place for that may soon be destroyed for a car park or a restaurant. I hope it isn't.
Coeloplana sp in ambient light.
These creatures are probably new to most divers and hopefully this has given you something of interest to look for and observe. The information on other websites will show, they have been recorded as being found on nudibranchs, echinoderms and soft corals and maybe the strange benthic Ctenophore will even establish a cult following - it is certainly interesting enough to do so.
I hope you found the brief information on these strange creatures interesting.
PS - January 2018, I found a diver in Indonesia who had seen these creatures in Lembeh Strait..he knew is as "Madonna's Tits" - looking at the photo immediately above, I won't comment.