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Name: Maya Ribeiro ID No: 816016576 Course: BIOL 1263- Living Organisms ІІ Lecturer: Dr. M. Hulme Assignment: Tutorial III- Essay

The term Echinodermata means ‘spiny skin’. Echinoderms belong to the kingdom Animalia, they live exclusively in marine habitats, are coelomates, have a triploblastic germ layer organization and adults possess radial symmetry while the larvae have bilateral symmetry. Their body lacks segments with a flat, star like, spherical or elongated body shape and they have an organ system grade of organization. Echinoderms lack a head and have tube feet for locomotion; they have a mouth on the ventral side and an anus on the dorsal side. Most Echinoderms are dioecious and a few are monoecious, they reproduce sexually by gamete fusion, asexually by regeneration and fertilization occurs externally. They lack a nervous system and excretory system, but possess an open circulatory system and a complete digestive system. Echinodermata all have a water vascular system comprised of canals and surface appendages that control feeding and locomotion using hydraulic pressure. The water-vascular system has soft membranes, which allows diffusion of nitrogenous and respiratory wastes through the body wall. It also carries out respiratory, excretory, and some circulatory functions within the animal. The individual sections of the water vascular system are the circular ring canal, the madreporite, radial canals, stone canal, tube feet and lateral canals as shown in the diagram below:

Diagram of the parts of the water vascular system of Echinoderms Source: https://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/15.43/

The madreporite is a light-colored, calcareous, perforated plate on the surface furthest from the mouth of the central disk. It acts like a pressure-equalizing valve and controls the entry and exit of water in and out of the vascular system of an echinoderm. The stone canal is a tube containing calcareous deposits that leads from the madreporite to the ring canal of the watervascular system surrounding the mouth. It transports water between the madreporite and the ring canal. The ring canal is the circular water tube surrounding the esophagus of echinoderms. There are a number of bulbous structures, called polian vesicles, which branch off from the ring canal and serve as reservoirs to maintain extra water stores. The ring canal transports water to the radial canals. Radial canals are ciliated, extending from the ring canal into each of the five arms to which it transports water and provides suction to the tube feet. Lateral canals branch from the radial canal and bring water into the ampullae and podia of the tube feet. They are lined with small hair-like, cellular projections (cilia) that beat back and forth continually to maintain water flow through the canals. Tube feet are extensions of the canal system that end in bulb-like, muscular ampullae. Tube feet (podia) aid in locomotion, gas exchange, feeding, attachment, and sensory reception. The ampulla contracts and forces water into the tube foot for locomotion. Podia are short, tubular extensions of the canal wall (usually with a sucker). The parts of the water vascular system within echinodermata is shown in the diagram:

Diagram of water vascular system in the context of an Echinoderm body Source: http://www.trendnet.me/sea-star-water-vascular-system.html

The water vascular system in Echinodermata aids in locomotion of the organism. When the ampullae muscles contract, water is forced into the suckered podia, which then extend outward. As the podia stretch, they can use their suckers to attach to a location further than their previous point of attachment. This results in a slow but powerful movement. The water vascular system in Echinodermata helps the organism to feed. When tube feet become extended, they can be used to generate small water currents toward the mouth region to assist in food collection. The water vascular system also provides excretory and respiratory functions. Most echinoderms lack respiratory or excretory organs, so the tube feet permit waste to diffuse out and oxygen to diffuse in via their thin walls. In conclusion, the water vascular system in echinoderms is a hydraulic system, such as sea urchins and sea stars, which extends along each of the body regions and has many external

projections called tube feet. It is used for locomotion, feeding, excretion and respiration. It is necessary in echinoderms because they lack a nervous system and excretory system. The individual parts of the water vascular system (the circular ring canal, madreporite, lateral canals, stone canal, radial canals, and tube feet) are well adapted for their respective functions and aid the organism in performing some of its biological functions.

Bibliography o Biology Discussion. (2018). Water Vascular System of Echinoderms. [online] Available at: http://www.biologydiscussion.com/invertebrate-zoology/phylumechinodermata/water-vascular-system-of-echinoderms/33754 [Accessed 13 Oct. 2018]. o Foundation, CK-12. 2018. "| CK-12 Foundation". CK-12 Foundation. https://www.ck12.org/book/CK-12-Biology-Advanced-Concepts/section/15.43/. o Hickman, Cleveland et al. “Animal Diversity.” McGraw-Hill, 2012. o Khanna, D. and Yadav, P. (2005). Biology of Echinodermata. New Delhi: Discovery Pub. House. o "radial canals." A Dictionary of Zoology. . Encyclopedia.com. (October 16, 2018). http://www.encyclopedia.com/science/dictionaries-thesauruses-pictures-and-pressreleases/radial-canals o Sea Star Water Vascular System 51920 | TRENDNET. Accessed October 17, 2018. http://www.trendnet.me/sea-star-water-vascular-system.html.