Subcapitulum

The subcapitulum (from Latin sub, "under", and capitulum, "small head"), also known as infracapitulum,[1][2] hypognathum[3] or hipognatum, refers to the ventral part of the gnathosoma (the part of the body comprising the mouth and feeding parts)[4] or the fusion of the palpal (of the pedipalps, the second pair of appendages) coxae (the point of union of the appendages with the body) and the labrum (the upper mouthpart) complex[3] present in some arthropods on which the mouth, pedipalps, mouthparts and pharynx are generally located.

It is delimited by the subcapitular apodeme (an ingrowth of the exoskeleton for muscle attachment), which separates it from the cheliceral (of the chelicerae, the first pair of appendages) frame.

The anterolateral parts of the subcapitulum might be equipped with cornicula (horn-like processes) or rutella (hypertrophied setae on the hypostome).

At the base of the hypostome, there can be sternal apophyses, that is, an outgrowth or process in the sternum (lower half of the body segment).

In comparison with other arachnids, the ricinuleid subcapitulum may result primitive, but it presents a specialization unique of the order; the coxal regions of the pedipalp are enlarged.