In spite of the similar tentacle structure and mechanisms of locomotion in A. japonicus of different sizes, their feeding rates vary. The time taken for a tentacle to feed decreased as the sea cucumber body grew. The intraspecific differences between morphological structures and feeding rates may be associated with the physical conditions and energy requirements during different growth periods. Holtz and MacDonald [26] found a positive correlation between tentacle insertion rate and the amount of food ingested in the sea cucumber Cucumaria frondosa. The larger size sea cucumber needed more food to maintain normal life activities. As a result, the larger size sea cucumber would have more fine tentacles and feed more quickly. We observed the tentacle locomotion in the condition of illumination in this study; however, A. japonicus might prefer to move and feed in dark environments. Notwithstanding this limitation, we did quantify feeding behavior at the tentacle level.