The animal kingdom is vast and consists of a large variety of species, some of which have developed similar body systems or body systems with the same end goal. Some scientists believe that specific traits such as defense mechanisms have evolved and been passed on as organisms become more complex. As with all things in evolution direct relationship is difficult, if not impossible to determine with absolute certainty. The striped skunk Mephitis mephitis and the sea cucumber Holothuria although strikingly different share particularly interesting defense mechanisms that consist of excreting either a liquid or their insides . Mephitis mephitis more commonly known as striped skunks are recognized mainly by their color and white stripe that runs on the back of their head, they belong to the kingdom animalia , phylum chordate and subphylum vertebrate (Dragoo ,2009) . Holothuria, also known as sea cucumbers are found in oceans all over the world (Barnes, 1987; Brusca and Brusca, 2003). The focus of this paper will be how the two organism's defense mechanism works and to compare any similarity.
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Skunks (Mephitis mephitis ) belong to the kingdom Animalia and the phylum chordate. Chordates are characterized by having bilateral symmetry, segmented body, three germ layers and a well-developed pharyngeal pouches present at some stage of development, ventral heart with dorsal and ventral blood vessels and a closed blood system as well as a complete digestive system (Grzimek ,1990). These animals are found in temperate climates that range from chaparral, forests, rainforests and scrub forests as well as urban suburban and agricultural settings (Gehring and Swihart ,2003). Skunks are polygamous and breeding season is February to March. Males are solitary and only interact with females at the moment of mating. Females are in charge of caring for the young and usually stay with the offspring a year after reaching full maturation. In females delayed implantation is involved and the gestation period is between 60 to 77 days (Wade-Smith, Richmond and Mead ,1980). Skunks are born blind, deaf and immature they stay with the mother in her den nursing for one month, 90% of them die after the first winter but in captivity they can survive as much as 15 years (Grzimek ,1990). These animals are nocturnal and burrow during the day in burrows made by other animals or under tree stumps and buildings. Both sexes hibernate from November until March and as many as six females can live in one burrow at one time (J. Dragoo ,2009). Skunks are opportunistic omnivores and will eat whatever is readily available. Some of the things it eats include : insects ( 70% of diet) , small mammals, crustaceans, grains, leave, etc. (Brusca ,2003). Because of their ability to emit foul smelling secretion from glands near their anus, most mammals do not come near them , however big birds such as the great-horned owl and the red-tailed hawk will attack it (J. w. Dragoo ,2009).
Sea cucumbers (Holothuria ) belong to the phylum Echinodermata and the class Holothuroidea. Echinoderms are distinguished by having a coelomic, water vascular system and pentaradial symmetry. Holothurians in turn are characterized by having feeding tentacles that extend from a circumoral ring. Individuals can range in size from 10 to 2000mm in length (Lawrence , 1897). These animals are found in saltwater environments mostly coastal areas with intertidal or littoral influences (Barnes ,1987). Holothurians are dioecious and have limited contact with their spawn after fertilization. The life cycle depends on the type of holothuria. Some are fertilized in the water and left free swimming, others are fertilized externally and pulled with the tentacles where they are placed in a adult's pouch where they are born through a small opening next to the anus (Brusca ,2003). They are usually sedentary or slow moving. Depending on the type of sea cucumber some can even walk on their elongated podia (R. D. Barnes ,1982). these animals are suspension/deposit feeders. Depending on the kind they will ether move around to "vacuum" the sea floor or wait stationary for the food to go to their tentacles where they trap it with mucus secreting cells (Brusca ,2003). They are very susceptible in their larvae stage but can defend themselves in adulthood with the help of the Cuverian tubules and the fact that they can expel their insides which will grow again (Thomas J. Delia ,1987)
Sea cucumbers have a very particular defense Mechanism. It is so particular because it involves the evisceration of the animal. The sea cucumber detaches entire organs to protect itself and depending on the type of sea cucumber it will be completely regenerated. Evisceration in holothurians is a complex process. It involves 1) a rapid softening of the attachment ligaments of the viscera and of the tendons of selected muscles to the cloaca, the mesenteries, and the body, localized softening of the body wall or the cloaca; and 3) a contraction of the muscles that easily stretches and ruptures the weakened structures, expelling the disconnected viscera (José E. García-Arrarás ,2002); (Carlos A. Díaz-Balzac , 2010); (José L. Quiñones , 2002)
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The Skunk's defense mechanism is a little different. It also consists on expelling something but this time it is a pungent smelling chemical. The secretion mechanism is less complicated. The muscle around the anal opening contracts and expels pungent musk which mixes up to 2- 5 meters after it is secreted and has a smell similar to rotten eggs with garlic (Andersen, Bernstien and Caret , 2002). Luckily for predators it only produces 15 cc of solution and it requires about 10 days to produce more to spray other victims (Andersen, Bernstien and Caret , 2002). This ridiculously pungent substances has been studied by many and found to derive its smell from several thiols (mercaptans), thioethers (sulfides), and disulfides which were identified by GC (Andersen, Bernstien and Caret ,2001); (Wood W. F. , 2002). Skunk spray is composed more specifically of (E)-2-butene-1-thiol, 3-methyl-1-butanethiol, and 2-quinolinemethanethiol, as well asacetatethioestersof each of these (Diaz-Miranda, Price and Greenberg ,2002). These compounds are detectable at concentrations of about 10 parts per billion (Wood W. F. ,2002).
These incredible animals with their strange defense mechanisms have both good and bad impacts on humans. Skunks help eliminate insect and rodent pests which would otherwise damage crops , transmit disease, etc. Skunks were also once desired for their fur but demand has gone down with the help of animal rights groups (J. Dragoo ,2009). Although very helpful to humans in some aspects skunks are also known to eat crops and domestic animals such as chickens. And as much as they help eliminate insect and rodent pests they might carry sylvatic rabies and pose a danger to humans and other animals (J. Dragoo ,2009). The sea cucumber is heavily used in Asia for food and as spice. It is also used as an aphrodisiac and as a medicine when it releases toxin from Cuvierian tubules(J. Dragoo ,2009). They pose no significant risks to humans and the only danger is that they might become extinct from overfishing.
Not only are the skunk and sea cucumber capable of defending themselves with incredible methods they are also great models for bio-mimetic devices as well as possible biological weapons. Currently under development is a T-antigen binding lectin with antibacterial activity from, sea cucumber (Holothuria scabra) which could possibly be involved in differential recognition of bacteria (Nagaraj M. Gowda ,2008). A study titled " GC/MS based identification of skunk spray maliciously deployed as "biological weapon" to harm civilians" (Wennig, Schneider and Meys , 2009) has helped scientist identify the possible uses and risks of skunk musk. There are many more ongoing projects and investigations to harvest these two animals' incredible abilities for the benefit and protection of man.
As we have seen briefly, skunks and sea cucumbers although very distant relatives display impressive defense mechanism both of which end up expelling either their organs or a pungent smelling musk. They are important not only because of the potential uses as discussed in previous paragraphs but also because their study provides us with invaluable information about our kingdom.
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