9.+Arthropoda+–+myriapoda

=SPECIES: SCUTIGERA COLEOPTRATA = = =

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**Classification/ Diagnostic characteristics**

 * They lost the ancestral condition of the coelom due to evolution. (14)
 * They have a hemocoel, i.e, the fluid from their open circulatory system bathes the internal organs before returning to the blood vessels. (14)
 * This phylum has an open circulatory system. (14)
 * An external protective covering called cuticle is present. This cuticle is secreted by the epidermis. (14)
 * They grow larger by molting, the process of shedding cuticle and replacing it. (14)
 * There are 4 groups: symphyla, pauropoda, chilapoda,diploda - all depending on the number of legs the organism has. (3)



**Relationship to humans**
Some can live inside buildings (ground levels of home). They are usually harmless to humans. They don't usually bite, but if they do, their bites are not strong enough to easily penetrate human skin. Bites feel similar to a bee sting and can cause redness and a little swelling. They can be beneficial to humans since they eat many pest organisms, such as cockroaches and silverfish. (5)

**Habitat and niche**
They prefer temperate climates and are often found in buildings.They can also survive in many humid habitats, as long as there is a place to hide, sufficient humidity and enough food.Often, they can be found in the dark under rocks or in crevices.However, they are most commonly found in bathrooms and basements due to their high humidity. (1)

**Predator avoidance**
If a predator is able to grab one of the S. //coleoptrata's// legs, it will remove the leg from its body and run away. The leg will continue to move around for several minutes, thus distracting the predator and allowing it to escape. S. coleoptrata molt frequently and will regenerate the lost leg. In addition to running away, myriapoda usually have repugnatorial glands, which are glands that secrete foul tasting compounds to keep predators away and serve as a self-defense mechanism. The first set of appendages on a chilopoda like the S. coleoptrata are usually modified into a pair of claws with poison glands that can be harmful or potentially fatal to victims. (6)

**Nutrient acquisition**
//Scutigera coleoptrata// is carnivorous.Their first pair of appendages on the trunk are modified into a pair of claws with poison glands, which centipedes use to capture prey—typically other arthropods. They hold food with their mouths and the necessary appendages. The food is digested internally. They crush their food with the use of mandibles. (7)

**Reproduction and life cycle**
__**LIFE CYCLE**__ : Immature S. coleoptrata hatch from the egg looking very similar to their adults, although they only have 4 pairs of legs. (1) Its life cycle consists of six larval molts, also called instars, and four post-larval instars, after they mature (12). After their 5th molt, they have all 14 legs and are mature. (1)

__**REPRODUCTION**__: Their reproductive behaviors are stimulated by pheromones and sound signals. During courtship, males tap pother centipedes looking for a receptive female. Once a mate is found, the male spins a silk pad in which he places his sperm. The female then takes the sperm pouch and fertilizes her eggs.(1)

**Growth and Development**
After hatching from eggs, these organisms closely resemble mature adult //S. coleoptrata.// Immature organisms only have four pairs of legs. //S. coleoptrata// molt five times, gaining more pairs of legs after each molt to total fourteen pairs of legs in the mature organism. Therefore, the older the organism gets the more legs it grows. (6)

**Integument**
Arthropods have exoskeletons with a layer of epidermis underneath. They have dorsally ventrally flattened bodies that are divided into fifteen segments. Each segment has one pair of legs that are banded. To capture prey, the first pair is modified into a poisonous fang. They have a very hard layer of skin made of chitin and sclerotin. This also provides arthropods with a nice level of protection. Additionally, their antennas are well- developed and bear compound eyes. (5)

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10 - 200 pairs of appendages that range in size from microscopic to 30 cm in length. These appendages that are manipulated by body muscles. When one leg is on the power stroke, the other leg is on the recovery stroke, i.e, alternate movement on two sides of the body (9).Many legs are helpful in preventing these fast moving organisms from tripping over. Leg movements are impacted by contact of the legs with the ground and the sensations from surrounding legs. (5)

**Sensing the Environment**
The //Scutera coleoptrata//, the "House Centipede" senses its prey through the use of long antennae that have olfactory cells that can smell its prey and also by touching its prey and surroundings. Additionally they use their eyes to sense changes in their environment. (5)

**Gas Exchange**
Appendages help in gas exchange. They have a trachael system for gas exchange. Air filled tubes called trachea are connected to openings on the abdomen and thorax called spiracles. Trachea branch into finer tubes called tracheoles that branch join tiny air capillaries, or the surface for gas exchange. When the animal needs to take in oxygen or release carbon dioxide, the muscular valves of the spiracles open. Air then diffuses in and flows to end up in the capillaries where gas exchange happens. (14)

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**Waste Removal**
They excrete nitrogenous wastes through Malpighian tubules. These tubules open into the gut present between the midgut and hindgut. Uric acid, potassium ions, and sodium ions of the extracellular fluid are actively transported into the tubules. They are then carried towards the gut. To recover the water, sodium and potassium ion are actively transported back into the extracellular fluid by the rectum and hindgut cells. An osmotic gradient is created as a result, and so, water is pulled out from the rectal contents. The final waste product, which also contains uric acid, is excreted out of the rectum. (4)



**Environmental physiology**
These species are ectotherms, which means that the interior body temperature relies on the external environment. Thus, they have developed several mechanisms to regulate their body conditions. For example, evaporation through skin surface helps in thermoregulation. Potassium levels in blood are kept low to regulate the temperature during winter. Malpighian tubules aid in salt control. The microvilli present in malpighian tubules maintain the osmotic balance by enabling reabsorption of ions. (8)

**Internal circulation**
These species have an open circulatory system, with hemocoel blood sinuses and heart that is behind or to the posterior of the body. There are no “respiratory pigments” in the plasma. Hemolymph is pumped from the hind and sides of the body. It then passes a series of valved chambers and to the aorta where it is discharged into the front of the head. It is carried to the wings, antennae and legs by accessory pumps before flowing back into the abdomen. (14)

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**Chemical control**
The endocrine system of myriapods is similar to that of vertebrates. A "neurohemal" organ produces and stores neurohormones. When needed, they are released and can stimulate other endocrine glands and non-endocrine targets. In myriapods, the brain, prothoracic glands (present near the neck), corpus allatum (back of the brain), neurosecretory cells present in the brain, ovary and testes are the major endocrine glands. Endocrine systems are essential in maintaining homeostasis during growth, molting, mate recognition and migration. (10)

=Review Questions: =


 * 1. How does this organism avoid predation? How is this an example of adaptation?**


 * Ans:** The organism can simply lose one or several limbs (it detaches) if it is grabbed by a predator. This is an example of adaptation because it increases the overall survival of the organism and was likely derived through the process of natural selection.


 * 2. When is the endocrine system important in a myriapod's life? What is its role?**


 * Ans**: Endocrine systems play an important role during the molting stage. During molting, endocrine systems help in maintaining homeostasis.


 * 3. Why is environmental physiology essential in //S. coleoptrata//? Name one physiology and how it helps.**


 * Ans**: Since the organism is an ectotherm, the internal temperature depends on the external temperature. Thus, adaptations are required for the survival when the temperature conditions are extreme. The Malpighian tubules help in thermoregulation by maintaining a low potassium concentration.


 * 4. Waste in animals is released in three forms - urea, uric acid and ammonia. What type of waste does //S. coleoptrata// produce? Why is this type of waste removal beneficial?**


 * Ans:** Waste is released in the form of uric acid. This type of waste removal ensures that minimal water is lost, and thus, is beneficial in conserving water.


 * 5. Two organisms of //S. coleoptrata// are observed in the lab. One has 8 legs while other has 10 legs. Based on this observation,** **which one is older? How do you know?**


 * Ans:** The specimen with ten legs is older since it has more legs. Every time S. coleoptrata molts, it gains more legs. So, the one with ten legs has undergone more molting and is thus, more mature and older.


 * 6. What advantage does the concurrent action of ion re-absorption and an open circulatory system provide?**


 * Ans:** The microvilli in the Malphigian tubules essentially pump ions right back into the body of the myriapod. Such reintroduction allows nearby valves and chambers or other tissue to make immediate use of them.

**Sources:**
[] (1) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4523776/figure/F1/ (2) [] (3) https://goodridgebiojohnsastrillo.wordpress.com/arthropods/excretory-system/ (4) http://animaldiversity.org/accounts/Scutigera_coleoptrata/ (5) https://www.thoughtco.com/house-centipede-scutigera-coleoptrata-1968230 (6) http://eol.org/pages/1033083/overview (7) http://www.natureworldnews.com/articles/18889/20151221/insects-keep-warm-winter-maintaining-salt-balance-researchers.htm (8) https://www.britannica.com/animal/arthropod (9) https://endocrinexhs.weebly.com/phylum-vii-arthropoda.html (10) https://www.britannica.com/animal/insect/Circulatory-system (11) [|Jacobs, Steve. “House Centipedes (Department of Entomology).” House Centipedes, Department of Entomology (Penn State University), Jan. 2013, ento.psu.edu/extension/factsheets/house-centipedes.]  (12) https://bugguide.net/node/view/337734 (13) Hillis, David M., et al. //Principles Of Life //. Sinauer Associates Inc., 2012. (14)