Solifuges are easily distinguished from other arachnids by their massive two-segmented chelicerae (jaws), bearing a flagellum in the adult male.
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Solifuges use the chelicerae for prey capture and feeding, fighting with conspecifics, defense, burrowing and mating.
Whereas in adult females the primary function of the chelicerae remains feeding, the chelicerae of adult males, which are often markedly dimorphic, serve a crucial secondary function - reproduction. The exact role of the chelicerae during mating remains poorly understood, however. The chelicerae are thought to subdue a struggling female (e.g., holding her hind leg), to induce or play a part in inducing a state of temporary
paralysis, to prepare the female for mating, and/or to transfer the sperm to the female gonopore.
The flagellum, found on the jaws of males is thought to play a major role in reproduction. The flagellum occurs only in adult male solifugae. There is considerable interspecific variation in both the form of the flagellum and in its articulation: it is fixed in some species and movable in others.
In most solifuge families, species identification is based primarily on features of the jaws and the flagellum.
In the family Solpugidae, the flagella are formed predominantly as a long bristle (shaft) bending backwards and pointing proximally towards the prosoma. The flagellum originates in a sort of bladder, a bulbous base immovably fixed to the fixed (dorsal) finger. The flagellar shaft is an elongated (usually whiplike), variously shaped chitinous portion of the flagellum, which contains two canals, one with an external opening thought to secrete a fluid which plays a part in reproduction. The other canal (hemolymph canal), is connected basally to the hemolymph, and blind
ending apically. The hemolymph canal probably functions to change the shape or direction of the flagellum. All composite flagella (comprising stalt, base and shaft) are probably able to change direction and/or shape, most plausibly through hemolymph pressure.
The precise functions of the flagellum remain elusive.
A possible mechanical function of the flagellum is likely facilitated by hemolymph action.
All flagella are either inserted in a distally directed position, or are able, probably by means of hemolymph pressure, to be directed distally by
rotation in the socket, as in Ceromidae, Daesiidae, Galeodidae, and Hexisopodidae or by projection of the flagellum, as in Solpugidae.
Solipugidae and most other families transfer the sperm indirectly with cheliceral fingers handling the sperm.
The flagellum may be inserted into the female reproductive tract after insemination and excrete a fluid within the female reproductive tract. A long whip-like flagellum can be inserted deep into the female genital tract, most likely extending along the oviduct proper and into the oviducal chamber where it may secrete the alembic fluid.
