Echinoderms: Part 3 - Unique Defensive Characteristics
Michael Paletta - Guest Author
Spiny Skin -
Echinoderms possess an interesting defensive structure called the pedicellaria. These external jaw-like structures are located not only on the ends of arms but are also found along the body. These structures help keep the multitude of larvae that are constantly looking for an attachment site from settling on the body surface of echinoderms. Furthermore, the external skeleton of most echinoderms is quite formidable, usually quite thick and hard containing spine, poison, toxic mucous or a combination of these.
Expulsion of internal organs -
When sea cucumbers are stressed either by being picked on by a fish or caught in a powerhead or pump, they will contract forcing out their digestive tract and a massive amount of tubules containing Holuthurin. This compound dramatically reduces the surface tension of water and it is hypothesized that this compound appears to inhibit the ability of fish to take in oxygen so they rapidly die when exposed to this toxin. This behavior is an attempt to get the offending party trapped in the filaments where it will suffocate, while the cucumber crawls away to regenerate a new digestive system. This compound is present in all of the sea cucumbers of the genus Holothuria, which unfortunately make up most of the species commonly kept in aquaria. Sea Apples, a close cousin of the sea cucumber, also possess a similar toxin that can kill all of the fish in an aquarium if it is disturbed.
Regenerative abilities -
Part 3 of 8. Continue reading:
Michael Paletta is the author of two books, "The Modern Marine Aquarium" and "Ultimate Reefs," and has acted as a consultant with the National Aquarium in Baltimore and the Pittsburgh Zoo Aquarium.