Reader Joe Dickinson finishes up his underwater series from Moorea with several invertebrates:
To give an idea of scale, when in a “closed” position, as below, these anemones are about the size of a soccer ball or even a basketball.
In this closer view, refraction through surface ripples makes patterns of rainbow colors.
Here are the gills of a spiral-gilled tube worm (Spirobranchus giganteus), protruding from a coral head.
I am fascinated by the diversity of colors and patterns (due to symbiotic algae) in the mantles of giant clams (Tridacna giga). Even close neighbors can be quite different. These clams also typically are imbedded in coral.
These clams have hundreds of simple eyes and retract the mantle if they detect motion nearby. Here is that last clam above after being startled.
The weirdest sighting this trip I at first took to be a giant, free-living marine worm, but it turns out more likely to be an enormous, elongated sea cucumber (at least two meters in length) similar to, if not exactly, the tiger-tailed sea cucumber (Holothuria hilla).
You can see tentacles around the mouth above right. When I waved my hand to direct a current at the “head”, it pulled in as below.
Here is a closer look at the tentacles when they opened back out. I would estimate the diameter of the main body at about 6 – 8 centimeters).
Finally, to prove I did occasionally get out of the water, here is a nice scene from the interior of the island.