Question

Sea cucumbers (see figure) are classic hydrostats- cylindrical in shape with a body wall surrounding a constant volume of water. Many sea cucumber species crawl along the substrate using peristaltic locomotion (waves of alternating muscle contraction) while some species burrow into the substrate, which requires force to displace sediment. How might (a) the fiber angle of the collagenous body wall and (b) the initial shape of the animal correlate with peristaltic locomotion versus burrowing?

Answer 1

Sea cucumbers are marine animals.

Properties-

1. Leathery skin
2. Elongated body
3. Single gonad
4. Cylindrical elongated nody
5. Mouth and excretory hole are located in opposite poles

• Kingdom- Animalia
• Phylum - Echinodermata
• Subphylum- Echinoza
• class-Holothuroidia

The fiber angle of the collagenous body wall and the initial shape of the animal correlate with peristaltic locomotion versus burrowing because:

Echinoderms has mutable collagenous tissues whose stiffness in neurally controlled.

Mutable collagenous tissue is composed of few cells and more extracellular material ( hydrogel of proteoglycans) in which collagen fibrils are embedded

Because of this, the body dermis of sea cucumber can exhibit 3 states:

1. Soft state
2. standard state
3. stiff state

This unique property of mutable collagenous tissues makes it being able to rapidly change its stiffness and extensibility under neural control. Hence the fibrils of echinoderm stretch, slide or reorient in real-time.

This observed stiffness and softening responses of sea cucumbers is due to the difference in ionic composition as well as due to neurotransmitters like acetylcholine.

Increased K+ concentration increases stiffness and decreased Ca+ decreases stiffness or increases softness.