Tube feet

Tube Feet

Sea urchin tube feet extended past the spines

Tube feet are small, flexible, hollow appendages found in echinoderms, such as sea stars, sea urchins, and sea cucumbers. These structures are part of the water vascular system and play a crucial role in locomotion, feeding, and respiration.

Structure

Tube feet are typically composed of a bulbous upper section called the ampulla and a lower, tube-like section that extends outside the body. The ampulla is located inside the body cavity and is connected to the tube foot by a narrow canal. When the ampulla contracts, it forces water into the tube foot, causing it to extend.

Podia of Colobocentrotus atratus

The tube foot itself is often equipped with a sucker at the distal end, which allows the organism to adhere to surfaces. The walls of the tube feet are muscular and can contract to retract the foot or to create suction.

Function

Tube feet serve multiple functions in echinoderms:

• Locomotion: By extending and retracting their tube feet, echinoderms can move across the substrate. The coordinated action of numerous tube feet allows for smooth and controlled movement.

• Feeding: Tube feet can assist in capturing prey or in manipulating food items. For example, sea stars use their tube feet to pry open the shells of bivalves.

• Respiration: Tube feet can facilitate gas exchange by increasing the surface area available for diffusion.

• Sensation: Tube feet are sensitive to touch and chemical signals, aiding in environmental perception.

Types of Tube Feet

Starfish tube feet

Different echinoderms have specialized tube feet adapted to their specific lifestyles:

• Suckered tube feet: Found in many sea stars, these tube feet have a suction cup at the end, allowing for strong adhesion to surfaces.

• Non-suckered tube feet: Found in some sea urchins, these tube feet lack a suction cup and are used more for sensory functions.

• Pincer-like tube feet: Some species have tube feet that end in small pincers, used for cleaning the body surface.

Examples in Echinoderms

T. gratilla podia

• Sea Stars: Sea stars, such as the Pycnopodia helianthoides, use their tube feet for locomotion and feeding. They can extend their tube feet through small openings in their ambulacral grooves.

• Sea Urchins: Sea urchins have tube feet that extend through their spines, aiding in movement and feeding.

• Sea Cucumbers: These echinoderms use their tube feet primarily for locomotion and respiration.

Related Pages

• Echinoderm
• Water vascular system
• Locomotion in echinoderms

Pycnopodia helianthoides on glass

Gallery

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  T. gratilla podia

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  Mithrodia clavigera

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  Pycnopodia helianthoides tube feet