Fig. [77].—Anaspides tasmaniae in natural position for walking, × 1. The last two pereiopods point backwards and are overlapped by the first two pleopods.
The Peracaridan features, uniting it especially with the Mysidacea, are the structure of the elongated heart, the filiform spermatozoa, and the fact that no complicated metamorphosis is passed through, the young hatching out in a condition similar to, though possibly not identical with, the adult form.
The Eucaridan, especially Decapodan, features are the presence of an auditory sac on the basal joint of the antennules, and the modification of the endopodites of the first two abdominal appendages in the male to form a copulatory organ.
A type of a new genus of this family was found by me in the littoral zone of the Great Lake of Tasmania at an elevation of 3700 feet, and named Paranaspides lacustris.
This little shrimp (Fig. [78]), which does not appear to grow to more than an inch in length, is totally different in appearance from Anaspides, being pale green and transparent, with a very marked dorsal hump as in Mysis, to which it bears a very striking superficial resemblance. It leads a more active swimming life than Anaspides, and with this habit is correlated the flexure of the body and the greater size of the tail-fan and the scale of the second antenna. The mandible is peculiar in being furnished with a four-jointed biramous palp, while that of Anaspides is three-jointed and uniramous, and the first thoracic appendage is provided with a setose biting lobe on the antepenultimate joint, thus more resembling a maxillipede. In other respects it agrees essentially in structure with Anaspides.
Fig. [78].—Paranaspides lacustris, × 4. a1, a2, First and second antennae; Ab.1, first abdominal segment; ep, epipodites or gills on the thoracic legs; md, mandible; Pl.1, first pleopod; T, telson; Th.8, eighth free thoracic segment; U, uropod, or sixth pleopod.
Fam. 2. Koonungidae.—The sole representative of this family, Koonunga cursor, has been recently described by Mr. O. A. Sayce,[[94]] of Melbourne University, from a small stream some miles to the west of Melbourne. Although plainly belonging to the Anaspidacea, this interesting little animal, which only measures a few millimetres in length, and follows a similar habit to Anaspides, running about with its body unflexed, differs from all the other members of the Division in possessing sessile instead of stalked eyes, in the first thoracic segment being fixed to the head, and in a number of minor anatomical points.
It is impossible at present to assign the Carboniferous forms (Gampsonyx, Palaeocaris, etc.) to their exact position in the Division, but it seems that they agreed more closely with Anaspides than with the other two genera. From the position in which the fossils are preserved, it would appear that they followed a similar walking habit to Anaspides, and that the body was unflexed.