The division Eucarida, on the other hand, including the Euphausiidae and the Decapoda, shows the converse of these characters. The carapace coalesces with all the thoracic segments, there is never a brood-pouch formed from oostegites, the hepatic caeca are much ramified, the heart is short, the spermatozoa are spherical with radiating pseudopodia, the development is indirect with a complicated metamorphosis, and the mandible is without a lacinia mobilis.

Corresponding divisions are made by Calman to receive the other Malacostraca, namely, the Phyllocarida for Nebalia, the Syncarida for Anaspides, and the Hoplocarida for the Stomatopoda or Squillidae.

The important array of characters which separates the Euphausiidae from the other Schizopods and unites them with the Decapoda can no longer be neglected, and the consideration of Anaspides and its allies will further emphasise the extreme difficulty of retaining the Schizopoda as a natural group. In the sequel Calman’s proposed scheme will be adopted.

DIVISION 1. SYNCARIDA.

There is no carapace, and all the eight thoracic segments may be free and distinct. Eyes may be pedunculate or sessile. The mandible is without a lacinia mobilis. There is no brood-pouch, the eggs being deposited and hidden after fertilisation. The spermatozoa are filiform, the hepatic caeca very numerous, and the heart tubular and elongated, with ostia only in one place in the anterior thoracic region. The auditory organ is at the base of the first antennae.

Order. Anaspidacea.

Fam. 1. Anaspididae.—The mountain-shrimp of Tasmania, Anaspides tasmaniae, was first described by Thomson[[90]] in 1893 from specimens taken in a little pool near the summit of Mount Wellington; it was redescribed by Calman,[[91]] who drew attention to its remarkable resemblance to certain Carboniferous fossils of Europe and N. America (Gampsonyx, Palaeocaris, etc.).

The creature appears to be confined to the deep pools of the rivers and tarns on the mountains of the southern and western portions of Tasmania.[[92]] The waters in which it occurs are always cold and absolutely clear, and there is no record of its living at altitudes much below 2000 feet, while it frequently occurs at 4000 feet. The body may attain upwards of two inches in length; it is deeply pigmented with black chromatophores, and it is held perfectly horizontal without any flexure. The animal rarely swims unless disturbed, usually walking about on stones and water-plants at the bottom of deep pools. In walking the endopodites of the thoracic limbs are chiefly instrumental, but they are assisted by the exopodites of the abdominal limbs.

When frightened the shrimp can dart rapidly forwards or sideways by the strokes of its powerful tail-fan, but it never jumps backwards as do the other Malacostraca. It appears to browse upon the algal slime covering the rocks and on the submerged liver-worts and mosses, but it does not refuse animal food, even feeding on the dead bodies of members of its own species. The thoracic limbs, which are all biramous except the last pair, carry a double series of remarkable plate-like gills on their coxopodites. The slender and setose exopodites of the thoracic limbs are respiratory in function, being kept in continual motion even when the animal is at rest, and serving to keep up a current of fresh water round the gills.

Anaspides shows a remarkable combination of structural characters, some of which are peculiar, while others are possessed in common with the Peracarida or Eucarida. The chief peculiar characters are the entire absence of a carapace, and the freedom of the eight thoracic segments, with eight free thoracic ganglia in the nerve-cord; the peculiar double series of plate-like gills; the structure of the alimentary canal; and the fact that the eggs, instead of being carried in a brood-pouch, or affixed to the abdominal limbs, are deposited under stones and among water-plants.[[93]]