When I bring home seaweeds for the hermit crabs, I always wash them well, sort through them to choose the best for planting in the aquaria, and set aside the broken and torn ones in clean water. Eventually, they will go on the garden, but there's usually something hiding in the lot. After a bit, tiny (really tiny, half-pinhead size) snails start to climb up the walls of the containers. Or assorted worms come to the surface as their oxygen evaporates.
This time, among the amphipods and worms, some little blackish lumps showed up along the water line. At first, I thought they were just shreds of hydroids, until one moved.
They were all about the same size, 2 mm. long, and oddly-shaped. I couldn't make sense of them until I saw them under the microscope.
These are baby nudibranchs, or sea slugs, probably Dotos, possibly Doto columbiana, the British Columbia Doto. As adults, they will be about half an inch long. They live among the hydroids, their hiding place and source of food.
The lumpy appendages along the back are the cerata. They contain branches of the digestive tract, and the colour depends on what they are eating, in this case, dark brown hydroids. An adult will have from 5 to 7 pairs of cerata. I see 5 here.
Towards the front there are two upright rhinopores, which dectect odors. The eyes (in the yellow patches) are rudimentary, and probably distinguish only light and darkness. The two white-tipped appendages in front are oral tentacles; more sensory organs, for taste and smell, and only the nudis know what else.
|Another nudibranch. Side view.|
After I'd taken a few photos, I moved the slugs to the second tank, the one without a water filter to trap them in. And also, a place without hermits competing with them for the hydroids. (The hydroid-infested eelgrass I gave to the hermits yesterday is pretty well all cleaned off now.)
|Two nudis making a doughnut on glass.|
I never expected to see them again, so tiny and in such a forest of hydroids, but this evening, two of them were feeding on the tip of a hydroid-coated seaweed stalk near the top of the tank.
I hope they like their new home and grow up fat and happy. Tweet