The physiological function of the coelom in starfish larvae and its evolutionary implications.
The coelom in the bipinnaria larva of Asterias acts as a buoyancy tank. The concentrations of magnesium and sulphate in the coelomic fluid are lower than in seawater, reducing the density. The coelomic epithelium is a secretory epithelium, probably secreting sodium or chloride ions that then draw in the counter ion and water. The rate of urine production is very high for an isotonic marine animal, compensating for the large surface/volume ratio of the coelom. This function would account for the precocious development of the coelom and its association with an excretory duct. It is proposed that the coeloms of other pelagic larvae such as the actinotroch of Phoronis and of echiuran larvae have a similar function and that this may have been an original function of the coelom, although in many phyla this function has been modified or lost.
Institute of Environmental and Biological Sciences, Lancaster LA1 4YQ, United Kingdom. h.latham@lancaster.ac.uk
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Potts
D000825:Animal Structures / Q000737:chemistry / Q000502:physiology*; D000818:Animals; D005075:Biological Evolution; D007814:Larva / Q000502:physiology; D012623:Seawater; D013215:Starfish / Q000502:physiology*