Echinoderms are, at least from a lay person’s perspective (including me I’m not a marine ecologist) are quite boring. The groups are all similar in appearance, and they are slow-moving bottom dwellers. That being said, when I saw the name of this issue’s animal on Imp’s list, I knew I had something that breaks the mold. So, without further ado, please meet the flower urchin.
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Oddity Ark #9 (#189)
Kingdom: Animalia
Phylum: Echinodermata
Class: Echinoidea
Order: Camarodonta
Family: Toxopneustidae
Genus: Toxopneustes
Species:pileolus (1)
Related Species: The flower urchin is one of four species found within the genus Toxopneustes.
Range: Flower urchins are found in water depths of up to 90m in depth in the Indian Ocean and western Pacific Ocean.
IUCN Status: The flower urchin is not currently listed on the International Union for Conservation of Nature.
Flowering Stone
The flower urchin is a large sea urchin which has a diameter of up to 20cm. The outer shell or test of the urchin comprises of five interlocking plates arranged around the urchin’s Aristotle’s lantern, an organ that acts as the mouth of the flower urchin. Along the gaps of the interlocking plates of the flower urchin are two rows of tube feet that allow the urchin to move across the sea floor. Unlike most sea urchins don’t have the long defensive spines, instead, the interlocking plates are covered in four types of pedicellariae that each have their own function. The first type of pedicellariae, is the ophicephalous pedicellariae which resembles the urchin’s tube feet save for the three claws on the tip of the appendage (2). The flower urchin uses these pedicellariae to clean algae off its test as well as parasites that are present on its surface.
Flower urchins are grazers, predominantly feeding on algae and organic detritus, as well as the bryozoans or moss animals. While the flower urchin has few predators, it is known to be predated upon by the crown of thorns starfish (Acanthaster planci) and the predatory soft coral Paracorynactis hoplites, with other predators deterred by the globiferous pedicellariae which are used to inject a defensive venom with the recurved fang like structures, arranged along the surface of the test. Another species immune to the venom of the flower urchin is the zebra crab (Zebrida adamsii), a parasitic species that lives on the surface of the urchin, where it damages the spines, feet, and pedicellariae of its host (3).
Flower urchins time their spawning with the tide and moon phase, releasing reproductive cells from their gonophores arranged across the test of the urchin. Both the sperm and egg cells of the flower urchin are free swimming and are capable of hybridizing with the closely related Toxopneustes elegans to form natural valid hybrids (4). Larval sea urchins live at the surface of the ocean as part of the plankton for several months, swimming and feeding with their twelve arms before maturing into adults and sinking to the sea floor.
Terrors of Toxicology #8 – Contractin A and Peditoxin
The flower urchin was considered ‘the most dangerous sea urchin’ by the Guinness World Records in 2014 (5), a statement that has some weight to it due to the cocktail of two toxic compounds that make up its venom. Injected through the tips of the globiferous pedicellariae, the flower urchin pumps the compounds into its attacker as long as contact remains with these structures. Because the fang-like tips is relatively fragile, they can break off tearing the venom gland and continuing to pump toxins in for hours after initial contact.
The first of these toxins, Contractin A attacks the nerve cells, slowing the transmission of impulses across the body as well as causing hemagglutination, the clumping of red blood cells, reducing the efficacy of oxygen transmission around the body. Recent studies may also suggest that Contractin A may also slow brain metabolism, but further studies are required to determine if this toxin is responsible, or if it can be contributed to a third chemical listed only as UT841 (6).
The second toxin, peditoxin comprises of the protein pedin and a toxic molecule known as peotoxin. The peotoxin is responsible to the majority of the symptoms of flower urchin intoxication including reduced body temperatures, muscle relaxation, and the victim slipping into an anesthetic coma, with higher doses inducing convulsions and eventually ending in death. The toxicity of peotoxin increases, however, when paired with pedin, which in itself is non-toxic but (7), which acts as an amplifier, with even small amounts of the combined peditoxin able to induce shock, anaphylaxis, and death in lab animals.
When injected into humans the venom not only causes immense pain, but also cause disorientation, muscular paralysis, numbness, and respiratory problems, all potentially lethal symptoms when encountering the flower urchin while swimming or diving. While no confirmed deaths from this species have been reliably recorded (8), it is considered medically significant due to a combination of toxicity, potentially hazardous locations of encounters, and the unassuming appearance of this species.
References
2. Simon E. Coppard; Andreas Kroh; Andrew B. Smith (2010). "The evolution of pedicellariae in echinoids: an arms race against pests and parasites" Acta Zoologica. 20 (2): 1–24.
3. Katsumi Suzuki; Masatsune Takeda (1974). "On a parthenopid crab, Zebrida adamsii on the sea urchins from Suruga Bay, with a special reference to their parasitic relations" Bulletin of the National Science Museum. 17 (4): 286–296
4. K. Fukuchi; T. Uehara (1994). "Hybridization between species of sea urchins Toxopneustes elegans and Toxopneustes pileolus". In Bruno David; Alain Guille; Jean-Pierre Feral; Michel Roux (eds.). Echinoderms Through Time. CRC Press. p. 669
5. Craig Glenday, ed. (2014). Guinness World Records 2014. Bantam. p. 30
6. Y. Zhang; J. Abe; A. Siddiq; H. Nakagawa; S. Honda; T. Wada; S. Ichida (2001). "UT841 purified from sea urchin (Toxopneustes pileolus) venom inhibits time-dependent 45Ca2+ uptake in crude synaptosome fraction from chick brain". Toxicon. 39 (8): 1223–1229
7. S. Kuwabara (1994). "Purification and properties of peditoxin and the structure of its prosthetic group, pedoxin, from the sea urchin Toxopneustes pileolus (Lamarck)". Journal of Biological Chemistry. 269 (43): 26734–26738
8. John A. Williamson; Joseph W. Burnett; Peter J. Fenner; Jacquie F. Rifkin (1996). Venomous and Poisonous Marine Animals: A Medical and Biological Handbook. UNSW Press. p. 322
Picture Credits
1. 60cb7c9c5d81e0220044cada_flower_urchin_facts_about_the_sea_urchin_flower_fcfe634971.jpg (640×480) (kidadl.com)
2. https://upload.wikimedia.org/wikipedia/commons/c/c8/Toxopneustes_pileolus_appendages.JPG
3. zebra-crab-andrew-martinez.jpg (900×600) (fineartamerica.com)
4. mushroom-shaped-toxic-flowers-on-the-most-toxic-sea-urchin.jpg (1920×1080) (localdivethailand.com)
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