Variability of sea spiders morphological characters (Pycnogonida) related on their habitat depth

The gradual alterations of the body proportions related to the increase of the habitat depths are exemplified by the selected pycnogonid species. The lengthening of trunk, abdomen and legs follow the increase of depth. In addition, lateral processes become wider, the ocular tubercles and the eyes get reduced, and some neothenic characters (three-segmented chelicerae in Colossendeis angusta and reduction of the denticulate spines in C. megalonyx tenera) appear in specimens living at the greater depths.