Body cylindrical, with five or seven pairs of feet, and some branchial vesicles; body and abdomen very puny. The Læmodipoda; Caprella, Cyamus.
Fam. 5. Turbinidenartige, Seitenasseln.
Body horny and distinctly ringed, mostly compressed, with perfect maxillæ; seven pairs of thoracic feet and branchial vesicles; abdominal feet rudder-shaped. They swim usually lying upon the side; many leap—Amphipoda; Flohkrebse or Gammarinæ.
Fam. 6. Buccinidenartige, Sohlenasseln.
Similar to the preceding family, but the body is depressed, and the abdominal feet furnished with branchial plates. The Isopoda; Oniscidæ, to which belongs the genus Armadillo.
COHORT III. KRACKEN-CRUSTACEA—KOBE.
3514. Body not tripartite; spiracula or air-openings; more than three pairs of feet, no wings. Here belong the air-breathing Crustacea; Scolopendræ, Acari, Scorpions, and Spiders.
These animals are abruptly distinguished from the preceding by a conversion of the branchiæ into spiral-shaped tracheæ, which ramify and traverse the whole body. They all therefore live in the air, and if they do also dwell in the water, they still come to the surface to inhale that element. The eyes are only simple points or ocelli, which are accumulated frequently upon the sides of the head.
The most inferior of them are distinguished from the preceding cohort, or the Asseln, by almost nothing save the essential character of their own cohort, the tracheæ. They have mostly a number of feet, and only simple eyes, as the Scolopendræ.
The following have a short body, in which the abdomen predominates; thorax and head connate; never more than four pairs of feet—Acari, Scorpions, and Spiders.