What is "foot tubercle"

Parapodium \Par`a*po"di*um\, n.; pl. Parapodia. [NL., fr. Gr. para` beside + ?, dim. of ? foot.] (Zo["o]l.) One of the lateral appendages of an annelid; -- called also foot tubercle.

Note: They may serve for locomotion, respiration, and sensation, and often contain spines or set[ae]. When well developed, a dorsal part, or notopodium, and a ventral part, or neuropodium, are distinguished.