Internal Anatomy

All organisms within the phylum echinodermata possess a water vascular system which is used for gas exchange, locomotion and feeding. The water vascular system is a set of fluid filled canals which are lined with ciliated walls which create internal currents. The water vascular system in sea cucumbers is pentaradial: there are 5 canals which lie within the dermis (Ruppert et al 2004). Unlike other echinoderms, the madreporite is not on the surface of the organism. The madreporite acts as a sewer cap if you like. It is a pore or plate which connects the water vascular system to the surrounding sea water. The madreporite in this case is suspended in the periviscal coelom (Conand 1993).

Seawater flows through the cloacal ducts and is turned into periviscal fluid.

Under duress the cucumber can contract and fluid is expelled from the anus It is replaced when the cucumber relaxes and extends.  S. hermanni are able to change internal fluid volumes.

As previously stated, the mouth and anus are at opposite ends of the organism. This indicates a flow-through gut. Stichopus hermanni constantly churn benthic sediments. They eat the sand and will digest the organic molecules within.

Main form of respiration comes from the respiratory tree that is attached to the cloaca, however some gas exchange occurs across the tube feet and buccal podia. The respiratory tree is similar to human lungs in the way it branches out. The respiratory tree will contract to expel water, and the cloaca contracts to push water into the tree (Ruppert et al. 2004).

Coalomic cavity and hemal system are used for internal transport. Heart is absent.

S. hermanni uses evisceration as form of defence. The gut is detached near the mouth and is forcefully ejected out of the anus. They can then regenerate the lost body parts (Ruppert et al. 2004).

Herman’s sea cucumber on possess a single gonad. They are broadcast spawners and the larvae are planktotrophic, however little is known about their reproduction and biology.