CHAIN-JELLY or COMMON SALP
Although described as a jelly, this organism is quite unrelated to the common jellyfish. Indeed, it belongs to a much more advanced place in the evolutionary scale, where it almost became a vertebrate, but for some unknown reason retreated and became more primitive in appearance. The long double chains are really only one phase in its life history, the colonial phase, and are formed asexually from a solitary parent by a budding process somewhat like that of certain plants. Each of the new individuals is able to produce eggs and sperms, and the eggs once fertilised hatch into tiny tadpole-like larvae which eventually grow into solitary individuals similar to the colonial form, but still clearly distinguishable. The solitary individuals then become parents of the new colonial generation.
The commonest New Zealand salp, Thalia, often occurs in enormous numbers in open waters particularly in summer months, and their presence in the water is quite unmistakable even to the casual observer. They seem to be a favourite diet of the snapper, particularly about spawning time, though being largely water they would not seem to be particularly nutritious and are often passed right through the alimentary canal without any sign of their being digested. A close relation of the chain-jelly is the fire salp.
by Richard Morrison Cassie, M.SC.(N.Z.), D.SC.(AUCK.), Senior Lecturer in Zoology, University of Auckland.