In May 2012, Ned returned from a dive in Lembeh, Indonesia, with images of this tiny, clear Melibe nudibranch. He had been working the very shallow black sand shelf with our guide, while I was below them at 60 feet, taking video of another, much larger species of Melibe. I was pretty satisfied with my Melibe -until I saw the image of his, which happened to be a species neither of us had ever seen before. I managed to talk them into going back to the dive site the next day on the off chance that we might find it again. Ned and our guide valiantly hunted for about 15 minutes before they abandoned me to my hopeless quest but I stayed with it for 90 minutes with no luck. Ned sent his photo off to Dr. Terry Gosliner who identified it as Melibe megaceras, a species he had described in 1987.
Video frame capture – you can see the size next to our guide’s 1/4-inch wide pointer.
May 2014 found us back in Lembeh Strait and on this particular dive, over on the opposite side of the bay at a famed site called Hairball. Our goal was a pair of Ambon Scorpionfish known to be in the area but another boat was positioned where we wanted to drop, so we opted for a fairly bare patch of shallow black sand nearby. Almost within a minute, our guide Man, motioned me over, pointing to the black sand, where I saw absolutely nothing. It took several iterations of the point-shrug-can’t see-show me again-pantomime before I realized that he had found another Melibe megaceras! It was so tiny (see in the video frame capture above how it sizes up to Man’s pointer) and clear but this time I could add one more Melibe to my life list! Video below:
Recently, during a get-together of diver friends, the subject of parrotfish cocoons came up – I don’t remember why – and surprisingly, several said they had never seen a parrotfish sleeping in a mucous cocoon. After thinking about it, Ned and I realized that in all the hundreds of night dives we’d made, we had only seen it maybe a half dozen times. We encountered it for the first time in the mid-90s off Key Largo while waiting for the coral to spawn. We didn’t see the coral spawn that night, but the parrotfish cocoon made our dive. Mucus, secreted from a gland below the operculum, enveloped the sleeping fish in a protective bubble. And until about four years ago, all I knew about this phenomenon was what was taught when I first started night diving: that the mucous cocoon prevented attacks from nighttime predators like moray eels, by masking the scent of the sleeping fish. That theory was proposed in the 1950s by the scientist (H.E. Winn) who originally described the mucous cocoon of parrotfishes.
In November 2010, marine researchers from the University of Queensland published their findings that proposed another theory behind the mystery of the fishy cocoons: the nighttime covering provides protections from blood-sucking parasites. In tests, when exposed to parasites, 95% of the fish not protected by cocoons were attacked while only 10% of those in cocoons were. They point out that this theory doesn’t have to be mutually exclusive with the moray eel predator theory.
Parrotfishes and some species in the related wrasse family sleep at night by bedding down directly on the sand or in holes in the reef, making them ideal targets for parasites that would have a more difficult time attaching to a swimming fish. Although we’ve only seen parrotfishes in cocoons, wrasses like the Bluestreak Cleaner Wrasse (Labroidesdimidiatus) and some in the genus Pseudocheilinus have been observed sleeping in mucous cocoons both in the wild and in aquariums.
I have posted a short video on our Blennywatcher YouTube channel or you can watch it below. (Note: We originally wrote about this in our June 2011 Critter Hunt column in Scuba Diving Magazine).
Lembeh Strait Indonesia, May 2014 ~ What if you carried your home around with you – one that you built yourself – what shape would it be? If you were a worm, then I guess a tube would make sense. I watched the tiny, one-and-a-half-inch, onuphid worm in its clear tube, struggling to negotiate the clumps of algae that covered the black sand slope: stretch forward and grab something, pause, yank the tube forward, feel around, reach sideways and grab something, pause, yank the tube sideways – whew – it seemed like a lot of work! The worm wasn’t anything new – we see them on many of our dives in Lembeh – but I was killing time, waiting for Ned and our guide, Man, to move up the slope, so I watched.
Polychaete worms in the genus Hyalinoecia (from hyaline, meaning transparent, glassy)inhabit clear tubes that they build by secreting a material, onuphic acid, the chemical composition of which has been of much interest to scientists. Other genera in the family Onuphidae build tubes, but they cement things to them like shells and sand and in many species the worms remain in one spot, tubes partially or totally buried in the sediment. But my worm was mobile, carrying its house with it and through the miracle of the macro extension on my camera port, I could see its entire iridescent body undulating and pulsing down the length of the clear tube.
The turning worm: doubled over in its tube.
Then it turned! The worm doubled over on itself – basically doing a back flip inside its tube – and exited out the other end to struggle off in the opposite direction. Whoa! Worm watching just got interesting – now I have questions. For starters, this suddenly doesn’t seem like a very good house design – open at both ends – like a soda straw. How would the worm, preoccupied with dragging itself around and foraging for food, protect itself from a rear attack? Is it even in danger of a rear attack – what, if anything, eats these worms?
After turning, the worm is about to emerge
It turns out that these worms build 2 – 3 pairs of membranous valves at each end of the tube. The valves open when the worm pushes out and close by the force of incoming water when the worm retracts. So the worm can operate out of whichever end is convenient and its rear is sealed and protected. As it grows, the worm lengthens its tube and the valves are removed and rebuilt closer to the entrance. And these valves are not constructed in a haphazard manner: the membranes making up a valve at the front end of the tube are placed opposite from each other; at the narrower, back end of the tube, they are offset. The placement of the valves in this very regular pattern is evident by the traces of the old membranes on the sides of the tube. On the front end, the pattern is “v” shaped and on the rear end, the pattern is zig-zagged.
In looking around for information about what preys on the worms, I found a mention of one in an aquarium that was eaten by another species of worm and another account of a dissected starfish that was chock full of the undigested tubes – really, the photo is pretty amazing – Echinoblog included the image in the post, When Starfish Eat Too Much!!
This is my new favorite invertebrate – well, almost… after ctenophores and skeleton shrimp, of course. To see the worm turning in its tube and moving around the bottom, check out my short video over on our BlennyWatcher YouTube channel or click on the video below. Note: all the images in this post are screen captures from the video:
Meet Malacoctenus carrowi, a newly described blenny known from the Cape Verde Islands in the eastern Atlantic. A year ago, we announced a Blenny Auction to raise funding to enable Dr. Peter Wirtz to collect another specimen and complete the research to formalize the description of the fish, [...]