BOOK-SCORPION, or FALSE SCORPION, minute arachnids superficially resembling tailless scorpions and belonging to the order Pseudoscorpiones of the class Arachnida.
Wasmann, who has compiled a list of nearly 1 50o species of insects, arachnids and crustaceans, inhabiting ants' nests.
The science of insects began with Aristotle, who included in a class "Entoma" the true insects, the arachnids and the myriapods, the Crustacea forming another class ("Malacostraca") of the "Anaema" or "bloodless animals."
Ray's "Insects" comprised the Arachnids, Crustacea, Myriapoda and Annelida, in addition to the Hexapods.
(London, 1900), and " On a collection of Insects and Arachnids " in Proc. Zool.
Arachnids are prodigiously numerous.
The first of these has, in Arachnids as in other Arthropods, its pair of appendages represented by the eyes.
The second has for its pair of appendages the small pair of limbs which in all living Arachnids is either chelate or retrovert (as in spiders), and is known as the chelicerae.
It is possible, as maintained by some writers (Patten and others), that the lobes of the cerebral nervous mass in Arach nids indicate a larger number of prosthomeres as having fused in this region, but there is no embryological evidence at present which justifies us in assuming the existence in Arachnids of more than two prosthomeres.
The coxal glands do not establish any special connexion between Limulus and Scorpio, since thay also occur in the same somite in the lower Crustacea, but it is to be noted that the coxal glands of Limulus are in minute structure and probably in function more like those of Arachnids than those of Crustacea.
- Stra ussDiirckheim (1) was the first to insist on the affinity between Limulus and the Arachnids, indicated by the presence of a free suspended entosternum or plastron or entosternite in both.
They have appeared independently in connexion with a change in the excretion of nitrogenous waste in Arachnids, Crustacea, and the other classes of Arthropoda when aerial, as opposed to aquatic, respiration has been established - and they have been formed in some cases from the mesenteron, in other cases from the proctodaeum.
Their appearance in the air-breathing Arachnids does not separate those forms from the water-breathing Arachnids which are devoid of them, any more than does their appearance in certain Amphipoda separate those Crustaceans from the other members of the class.
Applying these principles to the consideration of the Arachnida, we arrive at the conclusion that the smaller and simpler Arachnids are not the more primitive, but that the Acari or mites are, in fact, a degenerate group. This was maintained by Lankester in 1878 (19), again in 1881 (20); it was subsequently announced as a novelty by Claus in 1885 (21).
Though the aquatic members of a class of animals are in some instances derived from terrestrial forms, the usual transition is from an aquatic ancestry to more recent land-living forms. There is no doubt, from a consideration of the facts of structure, that the aquatic water-breathing Arachnids, represented in the past by the Eurypterines and to-day by the sole survivor Limulus, have preceded the terrestrial air-breathing forms of that group. Hence we see at once that the better-known Arachnida form a series, leading from Limulus-like aquatic creatures through scorpions, spiders and harvest-men, to the degenerate Acari or mites.
Other large Arachnids have not been derived from the scorpions directly, but have independently developed from aquatic ancestors, and from one of these independent groups - probably through the harvest-men from the spiders - the Acari have finally resulted.
When it is admitted - as seems to be reasonable - that the primitive Arachnida would, like the primitive Crustacea, be anomomeristic and anomotagmic, we shall not demand of claimants for the rank of primitive Arachnids agreement with Limulus and Scorpio in respect of the exact number of their somites and the exact grouping of those somites; and when we see how diverse are the modifications of the branches of the appendages both in Arachnida and in other classes of Arthropoda, we shall not over-estimate a difference in the form of this or that appendage exhibited by the claimant as compared with the higher Arachnids.
The fact that the single pair of prae-oral appendages of trilobites, known only as yet in one genus, is in that particular case a pair of uni-ramose antennae - does not render the association of trilobites and Arachnids improbable.
In living Arachnids, excepting the Pantopoda, it is either fused (with loss of its appendages) with the prosoma (Limulus, 1 Scorpio), after embryonic appearance, or is 1 Pocock suggests that the area marked vii.
The nomomeristic Arachnids comprise two sub-classes - one a very small degenerate offshoot from early ancestors; the other, the great bulk of the class.
- Nomomeristic Arachnids, in which the somites corresponding to mesosoma and metasoma have entirely aborted.
The Epectinate Arachnids do not stand so close to the aquatic ancestors of the Embolobranchia as do the Pectiniferous scorpions.
- These most strange-looking Arachnids occur in warmer temperate, and tropical regions of Asia, Africa and America.
- Degenerate Arachnids resembling the Opiliones in many structural points, but chiefly distinguishable from them by the following features: - The basal segments of the appendages of the 2nd pair are united in the middle line behind the mouth, those of the 3rd, 4th, 5th and 6th pairs are widely separated and not provided with sterno-coxal (maxillary) lobes, and take no share in mastication; the respiratory stigmata, when present, belong to the prosoma, and the primitive segmentation of the opisthosoma has entirely or almost entirely disappeared.
Newport, George, " Nervous and Circulatory Systems in Myriapoda and Macrourous Arachnids," Phil.
Xxxv., 1894; see also his " Origin of Vertebrates from Arachnids," ibid.
Remains of air-breathing insects, myriapods and arachnids show that these forms of life were both well developed and individually numerous.
Oieape, a mite), a genus of Arachnids, represented by the cheese mite and other forms.