Fig. 84—The Tasmanian "Mountain Shrimp" (Anaspides tasmaniæ), a Living Representative of the Syncarida. Slightly enlarged

c.gr., "Cervical groove," marking off the first thoracic somite; ii-viii, the remaining thoracic somites; 1-6, the abdominal somites

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Among the Crustacea of the Carboniferous and Permian epochs, there are a number of forms of which the affinities were until recently quite obscure. They have two-branched antennules, a scale-like exopodite on the antenna, and the last pair of appendages (uropods) form, with the telson, a tail-fan. In these points they resemble the shrimp-like forms, but there is no carapace, and all the somites of the thorax are distinct, so that the form of the body is rather that of an Amphipod or Isopod. On the discovery of the remarkable Crustacean Anaspides ([Fig. 84]), which lives in fresh-water pools in the mountains of Tasmania, it was pointed out that it agreed with the fossil genera Uronectes, Palæocaris, and their allies, in those very characters in which they differed from all other Crustacea, and that it must be regarded as a surviving representative of the ancient group to which the name of Syncarida had been given. The more recent discoveries of living forms, Paranaspides from the Great Lake of Tasmania and Koonunga from fresh-water pools near Melbourne, and of the fossil Præanaspides ([Fig. 85]) from the Coal-measures of Derbyshire, have tended to support this conclusion. There can be little doubt that the Syncarida arose during the Carboniferous epoch (or earlier) from primitive shrimp-like forms which lost the carapace; but, after flourishing for a relatively brief period, the group dwindled away, although a few survivors have lingered on, like so many other "living fossils," in the isolated Australian region.

Fig. 85—Præanaspides præcursor, One of the Fossil Syncarida, from the Coal-measures of Derbyshire. Slightly enlarged. (After H. Woodward.)

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