The key characteristic of sea stars that distinguishes them from other echinoderm classes includes thick arms ambulacra that extend from a central disk where organs penetrate into the arms. Sea stars use their tube feet not only for gripping surfaces but also for grasping prey. Sea stars have two stomachs, one of which can protrude through their mouths and secrete digestive juices into or onto prey, even before ingestion.
This process can essentially liquefy the prey and make digestion easier. Brittle stars belong to the class Ophiuroidea. Unlike sea stars, which have plump arms, brittle stars have long, thin arms that are sharply demarcated from the central disk. Brittle stars move by lashing out their arms or wrapping them around objects and pulling themselves forward.
Sea urchins and sand dollars are examples of Echinoidea. These echinoderms do not have arms, but are hemispherical or flattened with five rows of tube feet that help them in slow movement; tube feet are extruded through pores of a continuous internal shell called a test. Sea lilies and feather stars are examples of Crinoidea. Both of these species are suspension feeders. Sea cucumbers of class Holothuroidea are extended in the oral-aboral axis and have five rows of tube feet. Improve this page Learn More.
Skip to main content. Module Invertebrates. Search for:. Phylum Echinodermata Learning Outcomes Describe the distinguishing characteristics of echinoderms Identify the different classes in phylum Echinodermata.
Figure 1. They exchange the water dissolved gases present in the surrounding water by the simple diffusion method. Oxygen dissolved in the surrounding water diffuses into their papulae and carbon dioxide diffuses out through the papulae. They also have their water vascular system through which water enters their body. The water vascular system is simply the body coelomic cavity with a network of water vessels in the body of the starfish that is composed of canals connecting numerous tube feet.
The oxygen travels through the tube feet into the water vascular system and carbon oxide gets exhaled out all by simple diffusion method. Sea Urchins make use of their external gills as well as tube feet for respiration. They mainly use their 5 pairs of external gills for respiration. Their 5 pairs of external gills are present around the mouth attached to the peristomial membrane. They use their gills and tube feet to exchange gases i.
They also have a good water vascular system ending in the tubed feet. The water that enters the body through the water vascular system helps in the circulation of oxygen to all body cells and intaking out the unneeded carbon dioxide from the cells. Brittle stars use their respiratory organs named bursae singular: bursa for the exchange of gases between the external water environment and the body cells all by simple diffusion method.
These bursae are the cilia-lined sacs. Each bursa is present on the bottom of the central body disk just opening between the arm bases. Each of the bursae fits between the two stomach digestive pouches. Typically 10 bursae or you can say 5 pairs of bursae are found in these species. The water with dissolved oxygen in it gets inside these sacs and flows through the bursae by means of cilia or muscular contraction where the gaseous exchange takes place.
Oxygen gets transported throughout the body by means of the hemal system which is composed of a series of sinuses and vessels. The water vascular system also contributes to the oxygen transportation mechanism but its contribution is far less as compared to the hemal system. Sea cucumbers use their respiratory organs called respiratory trees present in their anus for breathing. They use their anus both for breathing and excreting.
Respiratory trees are situated at both sides of the digestive tract and is actually composed of a series of narrow tubules branching from a common duct. The gaseous exchange usually occurs across the thin walls of the tubules. Their respiratory trees branch in the cloaca just inside the anus, where they perform the exchange of gases by simple diffusion method.
They intake the oxygenated water through their anus and then expel the carbon dioxide dissolved water through it. They by contracting and expanding their bodies, drive water through the anal opening and then into the respiratory trees. The food then passes into the stomach, where it is digested.
Unlike the other echinoderms, brittle stars have no anus; they eject undigested material through the mouth. The class Holothruoidea is better known by as the sea cucumbers. Sea cucumbers are cylindrical echinoderm animals with feathery tentacles at the mouth end of their bodies. They are often mistakenly called worms. Some species resembles fat pickles a few centimeters long Fig.
Others are like thin tubes over a meter long Fig. These animals are common residents of reefs and rocky shorelines worldwide. A few species swim constantly in the water, seldom touching the bottom; they are the only members of this phylum to do so. Some Pacific islanders collect sea cucumbers, remove their intestines, and dry the muscular body wall, making a food eaten in many countries.
Unlike other groups of echinoderms, sea cucumbers have no large plates or ossicles forming a rigid skeleton. Because the spicules differ by species, they are useful in identification. Muscles in the body wall of many sea cucumbers are developed enough to aid in locomotion. When the muscles contract, the body becomes firm and rigid.
In some species the muscles are so thin that the internal organs show through the body wall. When these animals are taken from the water, the body wall collapses like thin plastic tubing.
The digestive system has a mouth at one end, a digestive tube down the center, and an anus at the other end Fig. The mouth is ringed with tentacles that are modified tube feet. Some species use their tentacles to take in sediment particles rich in plant and animal matter Fig. Other sea cucumbers extend their tentacles to snatch passing food particles detritus and plankton Fig. This behavior makes them look somewhat like sea anemones, and so this class is named Holothuroidea from the Greek root word holothuroid meaning like a polyp.
The digestive tube has a stomach and a long, thin, coiled intestine where food is digested. Indigestible sand and other particles are expelled through the anus. Much the same happens in earthworms, which literally eat their way through soil. The respiratory system of sea cucumbers is unusual in its arrangement. They breathe through an internal structure called a respiratory tree , which is attached to the intestine Fig.
Seawater taken in through the anus fills this branching structure, where body fluids absorb the oxygen. Because the anus is often open during this respiratory process, other organisms—small crabs and fish among them—sometimes enter and take up residence in the lower digestive tract and respiratory tree Fig. A few species of sea cucumbers have a set of tooth-like projections around the anus to ward off invaders. Some sea cucumbers have another bizarre way of protecting themselves.
Cuverian tubules are branches of sea cucumber respiratory trees in the form of long, slender threads Fig. These Cuverian tubules contain both sticky and toxic chemicals. When these sea cucumbers are disturbed, they can eject these sticky threads out the anus, thoroughly entangling any attacking predator Fig. The ejected tubules look like strands of limp spaghetti but stick like cobwebs.
Under favorable conditions, these internal organs soon regenerate. The sea lilies and feather stars reside within the class Crinoidea from the Greek root word crino meaning lily. Sea lilies are sessile organisms attached to the substrate by a flexible stalk Figs.
The digestive organs are in a bud at the top of the stalk called the calyx. The arms of the crinoid extend out from the calyx.
These arms are made up of the calcareous plates seen in other echinoderms. Like the brittle stars, they are jointed for flexibility. Each arm has am ambulacral groove containing tube feet in the center and is lined on each side with tubular extensions called pinnules. The feathery arms are used to collect food from the water, thus crinoids are filter feeders. Feather stars are similar in body form to sea lilies Fig. Rather than an attached stalk, feather stars have small flexible appendages called cirri at the base of the calyx.
These appendages allow feather stars to move around. Some feather star species can even use their arms to actively swim Fig. This document may be freely reproduced and distributed for non-profit educational purposes. Skip to main content. Search form Search. Join The Community Request new password. Main menu About this Site Table of Contents. Home Biological Invertebrates Phylum Echinodermata.
Phylum Echinodermata. MS-LS Use argument based on empirical evidence and scientific reasoning to support an explanation for how characteristic animal behaviors and specialized plant structures affect the probability of successful reproduction of animals and plants respectively. MS-LS Construct a scientific explanation based on evidence for how environmental and genetic factors influence the growth of organisms. MS-LS Gather and synthesize information that sensory receptors respond to stimuli by sending messages to the brain for immediate behavior or storage as memories.
MS-LS Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation. HS-LS Develop and use a model to illustrate the hierarchical organization of interacting systems that provide specific functions within multicellular organisms.
HS-LS Communicate scientific information that common ancestry and biological evolution are supported by multiple lines of empirical evidence. The content and activities in this topic will work towards building an understanding of the phylum Echinodermata. Introduction to Phylum Echinodermata Echinoderms are named for the spines or bumps covering the outer surface of the bodies of many of them Greek root word echino - meaning spiny ; Latin root word - derm meaning skin.
Voice of the Sea. Use investigative skills to compare different groups within the phylum Echinodermata. Further Investigations. Table of Contents: Phylum Echinodermata.
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