Tube feet (more technically called podia) are small active tubular projections on the oral face of an echinoderm, whether the arms of a starfish, or the undersides of sea urchins, sand dollars and sea cucumbers; they are more discrete though present on brittlestars, and have only a feeding function in feather stars. They are part of the water vascular system.
Structure and function
Tube feet function in locomotion, feeding, and respiration. The tube feet in a starfish are arranged in grooves along the arms. They operate through hydraulic pressure. They are used to pass food to the oral mouth at the center, and can attach to surfaces. A starfish that is overturned simply turns one arm over and attaches it to a solid surface, and levers itself the right way up. Tube feet allow these different types of animals to stick to the ocean floor and move slowly. Tube feet consist of two parts: ampullae and podia. Ampullae contain both circular muscles and longitudinal muscle, whereas the podia contain the latter only. The podia use a particular glue (no suction) to attach to the substratum.
The shingle urchin (Colobocentrotus atratus) has among the most powerful podia of all echinoderms.
Collector urchins (Tripneustes gratilla) have elongated podia.
The nail starfish (Mithrodia clavigera) has particularly strong podia.
Oral face of a sunflower sea star, Pycnopodia helianthoides.
Close-up on a P. helianthoides.
Podia of a sea cucumber (Holothuria forskali)
- "Morphology". Echinodermata. University of California Museum of Paleontology.
- Mah, Christopher L. (January 29, 2013). "Echinoderm Tube Feet Don't Suck! They Stick!". Echinoblog.
- Smith, J. E. (1937). "The structure and function of the tube feet in certain echinoderms" (PDF). Journal of the Marine Biological Association of the United Kingdom. 22 (1): 345–357. doi:10.1017/S0025315400012042. Archived from the original (PDF) on 2013-11-15. Cite uses deprecated parameter
- Mooi, R. (1986). "Non-respiratory podia of clypasteroids (Echinodermata, Echinoides): I. Functional anatomy". Zoomorphology. 106: 21–30. doi:10.1007/bf00311943.