Functional Anatomy of the Walking-Legs of Scorpionida With Remarks On Terminology and Homologization of Leg Segments

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Abstract
In the present paper a study is made of the tendons and joints of the walking-legs in Euscorpius flavicaudis (De Geer) (Chactidae), whilst several other species of scor- pions are mentioned also. Five new terms (a-, eu-, mono-, bi- and tridesmatic) are introduced in order to enable a precise and purely morphological description of joints and segments. The investigation summarized here has been carried out in order to determine the types of joints, to trace adesmatic joints and to denominate eudesmatic and adesmatic leg segments. Some structures described by MANTON (1958) have been further investigated and more exactly defined. The complete series of walking-legs is illustrated here in detail, just as the structure of the joints. In order to explain the positions of the leg segments and the directions of move- ment, the orientations of the planes of pseudosymmetry of the individual leg seg- ments have been established; they are illustrated here by diagrams. These diagrams are used here particularly to explain the tarsal torsion, i.e. the turning of the terminal segments as a compensation for the turning at the base of the leg. It is pointed out here that the shape of some segments, articulation points and joints are adaptations to life in burrows, just as the orientation of some muscles and the torsions in leg segments (resulting in an oblique position of the plane of pseudo- symmetry of the leg). The difference in function between leg I and leg IV is demon- strated by the position of the leg. Leg I is often functioning as a tactile organ and its terminal part is directed rostrally. The main function of leg IV is putting forth the propulsive force in locomotion; its terminal part is directed caudo-ventrally. In this way the useful effect of these legs (considering the functions mentioned here) is enlarged. In many respects the leg structures of the Scorpionida (which still are often considered rather primitive animals) appear to be highly specialized. A hypothesis is introduced concerning the origin of the flattened protuberances (gnathobases auct.) on coxae I and II, and concerning their relation to the sterna- pophyses of some other Arachnidea. The new term coxapophysis is introduced here for these protuberances. The erroneous usage of terms (among which the application of undefined or misleading terms) has led to a certain confusion in the morphological terminology of the Arachnidean legs. As a contribution to a correct and uniform terminology, much attention is paid here to an exact definition of terms, whilst a nearly complete list of synonyms from literature on walking-legs of Scorpionida has been compiled. An extensive list of the literature is also made.

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