Photo by Gary May
Redbait, photo by James Florence
Super klipfish on a colonial ascidian, showing single exhalant siphon for several inhalant ones. Photo by Guido Zsilavecz
Colonial ascidians, showing variety. Photos Pierre Niehaus.
Another colonial ascidian, photo Ros Morgenrood
Ascidians, or sea squirts as they are commonly known, are rather under-rated by divers, as many of them are somewhat drab and featureless. There are, however, many rather beautiful ones, as the images show, sporting delicate colours and interesting, unusual shapes.
Sea squirts are also under-rated as animals. They may appear like a sack with two siphons - one draws in water and nutrients, the other expels the water, but in reality they are more complex than their body shape would suggest. The larvae show this most clearly, in that they resemble tad-poles; they have a primitive backbone, nerve cord and tail. Only once they settle do they become the sack with siphons. Large animals are solitary, like red-bait or the one Gary May photographed, but others are colonial, like most others shown here.
Individual animals each have a inhalant and an exhalant siphon, but colonial ones may share a single exhalant one. This is clearly shown in the third image, where the large, yellow exhalant siphon is surrounded by numerous small inhalant ones.
While sea-squirts are common, they are not well studied, and hence names of species are often missing. This species may be Ascidia incrassata.
Thanks to Dr. Griffiths for information.
Two Oceans, A guide to the marine life of Southern Africa, GM Branch, CL Griffiths, ML Branch and LE Beckley, 1994.