Three hooks of O. compacta were examined with the scanning electron microscope (SEM). Their relative sizes are seen in the photograph below. Hook number 7 from the proximal end of the ventral hook series (ie, hook V7) was the largest club hook; hook D6 was its partner from the dorsal series. Note the large spike on hook V9.
Figure. Frontal views of hooks of O. compacta, D6 (left), V9 (middle) and V7(right), 72 mm ML, near the Hawaiian Islands, 22°45'N, 158°00'W. SEM photographs by R. Young.
Figure. Top-frontal views of hooks V7 (left) and V9 (right). The proximal lateral-lobe in V7 is nearly absent while the distal lateral-lobe is well-developed. The proximal lip of hook V7 has a strong hair-lip but the edge is not distinctly raised into a spike. In hook V9 the proximal lateral-lobe is absent and a large spike is present on the hair-lip. The lateral claw grooves are deep and define a narrow apical ridge on the claw. SEM photograph by R. Young.
Figure. Side views of the three hooks D6, V9, V7 (small to large). Left - View of proximal sides. Right - View of distal sides. Note the shape and size of the spike on the middle hook (V9). SEM photographs by R. Young.
Figure. Attachment-site views of the two hooks of the ventral series (hook V7 at the left, V9 at the right). SEM photographs by R. Young.