Morphological Variation of Hooded Hooks in Prionospio Japonica (polychaeta, Spionidae)

Observations of hooded hooks of Prionospio japonica by SEM have revealed that the number of apical teeth on the main fang varies from 6 to 12 within a single adult specimen. Termed outer apical teeth, these tend to decrease in number posteriorly along the length of body, and juveniles tend to have hooded hooks with fewer numbers of apical teeth. SEM observations have revealed further the presence of 0–5, smaller, median apical teeth on hooded hooks. Median apical teeth vary in number independently from the larger apical teeth, and a total of 42 arrangements of apical teeth can be observed on a single adult specimen. These findings suggest that the arrangement of apical teeth of hooded hooks should be used with caution in the taxonomy of Spionidae.