A pediveliger uses its foot to crawl.
The foot is an extendible muscular organ located in the mid-ventral region of the mussel, and its primary function is locomotion. The byssal gland is located within the foot, and it produces secretions which are used to form byssal threads for attachment to substrates.
The process of byssal thread formation begins as the foot is pressed firmly against a substrate so that the mussel can secrete a plaque. After the plaque is formed, secretions released by the byssal gland are directed down the byssal canal to the base of the foot. The fluid hardens, forming individual byssal threads. A mussel 2.5 cm in length may have up to 600 threads holding it in place (Claudi and Mackie 1994). The zebra mussel can detach from the substrate by secreting enzymes at the base of the byssal mass and reattach by laying down new threads at another location. Composition and morphology of the zebra byssus have been examined in detail by Frisina and Eckroat (1992) and Bonner and Rockhill (1994).
Byssal attachment is beneficial to the zebra mussel for two primary reasons:
(1) It does not have to expend energy to maintain its position on the substrate.
(2) When the water level falls, an attached mussel can withdraw its foot and tightly close its shell to prevent dehydration (Eckroat and Steele 1993).