Abstract
ONE of the most remarkable and unexpected zoological results of recent explorations in Antarctic seas has been the discovery of Pycnogonida (so-called “sea-spiders”) having five instead of the usual four pairs of legs. Soon after the return of the Discovery expedition, Mr. T. V. Hodgson described Pentanymphon antarcticum, and a little later he had the good fortune to find, among the collections of the Scottish National Antarctic Expedition, the long-forgotten Decolopoda australis described by Eights more than seventy years ago. A second species of Decolopoda was added by Prof. E. L. Bouvier from the collections of the French Antarctic Expedition in the Français. The most surprising circumstance connected with this remarkable departure from what had been regarded as the normal structure of the Pycnogonida was that it appeared in two genera by no means closely related to each other, but, on the other hand, not dissimilar in general structure from other "normal" genera. Thus Pentanymphon is indistinguishable, except in possessing an extra pair of legs, from Nymphon, while Decolopoda is only a little more divergent from Colossendeis. From the point of view of phylogeny, two explanations of these conditions may be offered. Most authorities, for example, Prof. Bouvier and Prof. D'Arcy Thompson (in the “Cambridge Natural History”), adopt the view that the ten-legged condition is the primitive one, and has been retained by the most primitive members in two divergent branches of the group. The other explanation, first suggested by Prof. G. H. Carpenter and advocated by the present writer (Science Progress, April, 1909), is that the decapodous condition is a recent development, appearing independently in the two cases.
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CALMAN, W. Antarctic Pycnogons. Nature 84, 104 (1910). https://doi.org/10.1038/084104a0
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DOI: https://doi.org/10.1038/084104a0
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