Work on the systematics of a large collection of Antarctic Pycnogohida has revealed very forcibly the limitations of existing systems of classification of this group. In an attempt to rectify some of these shortcomings for a monograph on the pycnogonid fauna of the Ross Sea area, the author has been led to seek new characters and character states which will be useful in taxonomy. Virtually nothing is known of pycnogonid behaviour and ecology, and it seems unlikely that additional knowledge in these fields will be forthcoming in the near future. Our knowledge of pycnogonid comparative anatomy and histology is also very slight. However, the Pycnogonida do lend themselves very readily to mensural description of much of their form. It is true that the expressions of some characters are more simply described by the traditional vocabulary of experts in the field (e.g., ovigeral spine shape), but for other characters this self-same vocabulary may be a source of confusion, as, for instance, in the description of proboscis shape. A morphometric study involving: some 160 specimens of three species revealed that certain simple statistical hypotheses on relative growth can readily be proposed. The values to practical taxonomy and the possible functional interpretation of these hypotheses, in the light of existing information on pycnogonid anatomy, are discussed in the following pages. The work was supported by National Science Foundation Grants Numbers G 14107, G 19338, and G 17890. Part of the work was carried out at the USARP Biology Laboratory at McMurdo Sound, Antarctica, and the author wishes to acknowledge his gratitude for the assistance and hospitality given to him by Dr. Donald E. Wohlschlag, the Director of the laboratory.