[Gastropoda] Chitinous teeth placed in evaginable sacs (the hook sack) at both sides of the radula probably modified parts of the jaw found in most Gymnosomata; the hook sacs are buccal organs in the head under the hood and are evaginable.

[Polychaeta] Stout-shafted simple chaetae which may be distally curved or toothed.

[Chaetognatha] Slightly claw shaped, curved, hard structures at the anterior of the head; also known as grasping hooks or spines.

Alternative form for hook : hooks.