Order IV. Palpigradi.
Minute Arachnids with three-jointed chelate chelicerae, and with the last two joints of the cephalothorax free. The abdomen consists of eleven segments with a fifteen-jointed flagellum.
In 1885 Grassi discovered, at Catania, a minute Arachnid which did not fall into any of the established orders of Arachnida. He named it Koenenia mirabilis. In 1893 Hansen collected several specimens in Calabria, near Palmi and Scilla, and carefully redescribed the species in conjunction with Sörensen.[[322]] It has been studied still more minutely by Börner.[[323]]
There is a “head” portion, covered by a carapace, and bearing the chelicerae, pedipalpi, and two pairs of legs. The two free thoracic segments bear the third and fourth pairs of legs, recalling the Schizonotidae (see p. [312]), where the portion of the thorax bearing these legs is separate, though covered by a single dorsal plate. There are no eyes, but two hair-structures, believed to be sensory, are present on the cephalothorax, and Börner has observed openings in the second joint of the first pair of legs which have all the appearance of “lyriform” organs, as found in Spiders (see p. [325]).
The last three abdominal segments narrow rapidly, the last bearing the anus. A fifteen-jointed caudal flagellum is carried, Scorpion-like, above the animal’s back. The body and tail are each about a millimetre in length, and the animal is of a translucent white colour.
The mouth is extremely simple, being merely a slit upon a slight eminence. There are two sternal plates beneath the “head,” and one beneath each free thoracic segment. The genital operculum is complicated, and is situated beneath the second abdominal segment.
Fig. [216].—Koenenia mirabilis, much enlarged. (After Hansen.)
Since 1885 several other species have been discovered in various parts of the world. Two American forms possess three pairs of lung-sacs on segments 4, 5, and 6 of the abdomen. Rucker[[324]] has suggested for them the generic name of Prokoenenia, including P. wheeleri, Rucker, from Texas, and P. chilensis, Hansen, from Chili. The others, styled by that author Eukoenenia, have no lung-sacs. There are about ten species, mostly from the Mediterranean region, but E. augusta, Hansen, is found in Siam, E. florenciae, Rucker, in Texas, and E. grassii, Hansen, in Paraguay.