The Importance of Being Honest: The Sea Cucumber Spills All

Sea Cucumbers make up 90% of the biomass on deep sea floors

Sea Cucumbers make up 90% of the biomass on deep sea floors

You have heard the proverb, honesty is the best policy. These wise words seem to extend to the animal kingdom as well, as the sea cucumber’s behaviour demonstrates: for the sea cucumber, spilling its guts – pun intended – can save its life.

Sea cucumbers are marine animals that belong to Phylum Echinodermata and are of the class Holothuirodea. Now, appearances are deceiving. The cooked sea cucumber you usually encounter may appear monumentally boring but it has a quirky natural defence that will either enthral you or make you retch in response.

Here’s a video of an intentionally provoked sea cucumber, with a background commentary that does not reflect the most brilliant of humans:
(please do not provoke sea cucumbers in real life just to watch them vomit)


When threatened, most species of sea cucumbers may expel all or parts of their internal organs through the mouth or anus, in order to distract or scare their predator away. For some species, toxins may also be released during this process of evisceration. Some sea cucumbers may expel sticky toxic strings called Cuvieran tubules which either poison the predator or immobilise it, giving the sea cucumber ample time to escape. Like its relative, the starfish, sea cucumbers can regenerate their internal organs over one to five weeks.  

Besides being the Claire Bennets of the Sea, sea cucumbers play a significantly fundamental role in deep sea ecosystems. Their diet of detritus contributes to nutrient recycling and their larvae are part of the plankton-based food chains. However, sea cucumbers, especially the edible ones, are at risk of being overharvested. In addition, land reclamation leading to habitat loss also threatens the survival of these animals. Without sea cucumbers, ecological systems will be upset and our very own survival placed at stake.

Therefore, save the sea cucumber, save the world.


VandenSpiegel, D., M. Jangoux & P. Flammang, 2000. Maintaining the line of defense: regeneration of Cuvierian tubules in the sea cucumber Holothuria forskali (Echinodermata, Holothuroidea). The Biological Bulletin, 198 (1): 34-49.

“Shedding New light on the Humble Sea Cucumber,” by N. Alcock. Aquatic Biodiversity & Biosecurity Update, 2003. Hosted on National Insitute of Water & Atmospheric Research: (accessed on 6 April 2010).

“Sea cucumbers (Holothuroidea) on the Shores of Singapore,” by Ria Tan. WildFactSheets, December 2008.  Hosted on WildSingapore: (accessed on 6 April 2010).

“Sea cucumber spills its guts,” by danyoferit. Youtube Channel, 29 December 2008. URL: (accessed on 6 April 2010).

“Sea cucumber,” by Jack Jackson. National Geographic: Sea Cucumbers. URL: (accessed on 6 April 2010).


Creatures of the earth engage in various strange mating behaviors. Male giraffes drink the urine of the females; red-sided garter snakes annually form mating balls of up to 30,000 strong and the reproductive organs of male wasp spiders snap off in the female during reproduction, but ‘penis fencing’? What in the world?



‘Penis fencing’ is an unusual reproductive activity commonly practiced by the marine flatworm (Pseudobiceros hancockanus), which can grow up to about 4-6cm long. Basically, ‘penis fencing’ is an unassuming phrase that biologists use to describe the vicious battle between two hermaphrodite flatworms consisting of each of them trying to stab the skin of the other using one of its two penises. This dual may last an hour and result in gaping wounds on the body of the loser. The ritual is done to facilitate the delivery of sperm from one flatworm to another to ensure reproduction, where the first successful ‘stabber’ becomes the de-facto male and the other, the de-facto female. The de-facto female then has bear the burden of motherhood while healing her wounds.

One might wonder what motivates this seemingly placid creature to engage in such ferocious behavior against its own kind even in the absence of any kind of sex drive. Scientists suggest that it is the result of a cost-benefit analysis, where members of the hermaphrodite population weigh the benefits of stabbing, against the costs of being stabbed. The benefits of stabbing include holding control of the fertilization process and gaining direct access to the eggs under the skin of the de-facto female. In addition, the de-facto males would have the valuable opportunity to pass on their genes to even more offspring while having fewer wounds to heal. On the other end, the costs of being stabbed include expanding copious amounts of energy caring and developing the eggs whilst healing gaping wounds.

Evidently, the tremendous benefits of stabbing another vastly outweigh the costs of being stabbed, which might serve to explain why marine flatworms approach this supposed act of ‘love’ in such a primal, warlike fashion.


“Fighting to mate: Flatworm penis fencing,” by Leslie Newman. PBS, n.d. URL: (accessed on 5 Apr 2010)

N. K. Michiels & L. J. Newman, 1998. Sex and Violence in Hermaphrodites. Nature, 391: 647.

Flatworms penis fencing by TheAwkblog Youtube Channel, 18 March 2009. URL: (assessed on 5 April 2010)

“Spiders sacrifice genitals to ensure paternity,” by Sarah Bartlett. Cosmos Magazine, 9 Mar 2007. URL: (assessed on 5 April 2010)

“Giraffes,” by Animal Corner, n.d. URL: (assessed on 5 April 2010)

“The Flatworms” by Lost In Arizona. Scienceray: The Great Barrier Reef: Jewels of the Sea. URL: (assessed on 5 April 2010)

See Shockingly Swift Shell-Shattering Shrimp Strike. Sh-

Fig. 1 - Peacock Mantis Shrimp (odontodactylus scyllarus)

Fig. 1 - Peacock Mantis Shrimp (odontodactylus scyllarus)

The mantis shrimp is probably one of the most outlandish looking animals on the face of this planet. Looking like an odd mix between a praying mantis and a large terrestrial bug, these predacious creatures feature some of the most highly evolved physical attributes of any invertebrate known to man. These marine crustaceans belong to the order stomatopoda, comprised of around 400 recognised species that are either identified as smashers or spearers according to the shape of their main forelegs and the use of them in obtaining prey.

Fig. 3 - Club-like smashing dactyl

Fig. 2 - Club-like smashing dactyl

Figure 2 shows the one of the massively muscled main arms of a smashing mantis shrimp. Smashers like the Peacock Mantis Shrimp in Figure 1 drive their club-like elbows into their prey at blinding speeds- up to 2300cm/s in a strike lasting 0.0027ms, the fastest strike of any creature on earth (Patek and Caldwell, 2004). They have earned the nickname ‘thumb splitters’ by divers who have inadvertently gotten to close to these crustaceans, whose blows easily render skin and flesh to the bone.

In a bid to understand this process, researchers at the University of California, Berkeley utilised high-speed video cameras with frame rates of 100000 frames/s. Here they discovered the truly devastating nature of smashing mantis shrimp strikes when they observed the phenomena known as cavitation and sonoluminescence occurring during each attack (Patek and Caldwell, 2005).

Video 1. High-speed footage of club-footed stomatopod strike

The footage above shows the process of one species of smashing stomatopod, odontodactylus scyllarus, bullying a snail. In layman terms, besides the nasty impact, the strike agitates the water near the point of impact so much that a flash of light, extreme heat and a damaging sonic wave are produced. From the snail’s perspective it is akin to getting hit by a speeding train laden with volatile explosives, that can hit you again and again. And again.

Video 2.  Peacock Mantis Shrimp (odontodactylus scyllarus) feeding

As observed in the clip above, mantis shrimp attack with astounding ferocity. Bear in mind that sound of the stomatopod’s strikes are being recorded from outside of the tank, implying some serious impact. Also observed from the video is the surprising agility of all mantis shrimp. Unlike most slow moving crustaceans, stomatopods are aggressive, highly mobile creatures that actively seek out their prey. They routinely leave the seabed and are swift swimmers that easily overpower fish that swim above the seabed.

Fig. 3 - Complex compound eyes of

Fig. 3 - Complex compound eyes of the Peacock Mantis Shrimp (odontodactylus scyllarus)

Stomatopods are also known to have the most developed compound eyes of the animal kingdom. They have incredibly sophisticated depth perception and can detect both circular and linear polarised light, a feature as yet undiscovered in any other animal (Kleinlogel and White, 2008). This enables them to maintain perfect vision in an environment that is subject to constant ambient light changes. The presence of transparent or camouflaged prey and predators prove no challenge or threat to a creature with such well-developed eyes (White, 2008)

The aggressive behaviour of this intelligent predator and the highly specific physical attributes they display seem to be the result of an evolutionary path taken to ensure survival in an ultimately competitive environment (Caldwell and Hugh, 1975). Club-footed mantis shrimp like the Peacock Mantis Shrimp (odontodactylus scyllarus) shown in the videos above live amongst rocks and coral formations in tropical waters that are teeming with life. Competition within semi-permanent rock burrows is rife, and encounters with various other vertebrates and invertebrates in this crowded habitat have caused an evolutionary ‘arms race’ amongst the reef’s inhabitants (Caldwell and Hugh,1975).

Their highly developed mobility, forelegs and compound eyes are the reasons why stomatopods like odontodactylus scyllarus flourish as predators.



Figure 1. “Mantis Shrimp” by buzzthediver, (20th Feb 2010) Accessed 1sp April 2010, under Creative Commons License. URL:

Figure 2. “Smasherrap” by Dr. Roy Caldwell, (July 2001) Accessed 1st April 2010, University of California Museum of Paleontology. URL:

Figure 3. “Mantis Shrimp” by Enje, (18th May 2009) Accessed 31st March 2010, under Creative Commons License. URL:

Video 1. “High Speed Footage of Mantis Shrimp Strike” by Sheila Patek (16th Sept 2005) (Taken on an Ultima APX high speed camera with Multi-Channel Data Link – Photron from Department of Integrative Biology, University of California, Berkeley., CA, USA). Uploaded by asemoknyo (1st April 2008) Accessed 23rd March 2010, URL:

Video 2. “Flawless Victory!!! Baraka Wins!!!” by bcgeazy, (28th June 2007) Accessed 22nd March 2010 . URL:

Patek, S. N., Korff, W. L. and Caldwell, R. L. (2004). Deadly Strike Mechanism of a Mantis Shrimp. Nature 428, pp.819-820 URL: (Accessed 27th March 2010.)

Patek, S. N., Korff, W. L. and Caldwell, R. L. (2005). Extreme Impact and Cavitation Forces of a Biological Hammer: Strike Forces of the Peacock Mantis Shrimp (odontodactylus scyllarus). The Journal of Experimental Biology 208, pp.3655-3664 (The Company of Biologists, 2005) URL: (Accessed 27th March 2010)

Caldwell, R. L. and Hugh, D. (1975) Ecology and Evolution of Agonistic Behaviour in Stomatopods. Naturwissenschaften 62, No.5, May 1975 pp.214-222 (Springer Berlin/Heidelberg,1975) URL: (SpringerLink date: 12th Dec 2004) (Accessed 1st April 2010)

Kleinlogel S. and White A. G. (2008) The Secret World of Shrimps: Polarisation Vision at Its Best. PLoS ONE 3(5): e2190.doi:10.1371/journal.pone.0002190 URL: (Accessed 1st April 2010)

White A. G. (2008) in “Weird Beastie” Shrimp Have Super-Vision, by Minard, A. (19th May 2008) National Geographic News. URL: (Accessed: 1st April 2010)