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Nervous system

The nervous system in these animals is a relatively simple structure with a nerve ring at the center and five radial nerves extending outward along the arms. Structures analogous to a brain or derived from fusion of ganglia are not present in these animals.

Excretory system

Podocytes, cells specialized for ultrafiltration of bodily fluids, are present near the center of echinoderms. These podocytes are connected by an internal system of canals to an opening called the madreporite    .

Reproduction

Echinoderms are sexually dimorphic and release their eggs and sperm cells into water; fertilization is external. In some species, the larvae divide asexually and multiply before they reach sexual maturity. Echinoderms may also reproduce asexually, as well as regenerate body parts lost in trauma.

Classes of echinoderms

This phylum is divided into five extant classes: Asteroidea (sea stars), Ophiuroidea (brittle stars), Echinoidea (sea urchins and sand dollars), Crinoidea (sea lilies or feather stars), and Holothuroidea (sea cucumbers) ( [link] ).

The most well-known echinoderms are members of class Asteroidea, or sea stars. They come in a large variety of shapes, colors, and sizes, with more than 1,800 species known so far. 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.

Explore the sea star’s body plan up close, watch one move across the sea floor, and see it devour a mussel.

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. These are the only echinoderms that demonstrate “functional” bilateral symmetry as adults, because the uniquely extended oral-aboral axis compels the animal to lie horizontally rather than stand vertically.

The sea star in photo a is red and white, with a thick squat body and protruding spikes. The brittle star in part b is brown with a flat, pentagon-shaped body. Thin striped legs extend from each point of the pentagon. Photo c shows a sea urchin with a round, black body and very long, thin, black spines. Photo d shows a sea lily that has appendages resembling branches of a spruce tree. Photo e shows a log-shaped sea cucumber with spikes extending from its body.
Different members of Echinodermata include the (a) sea star of class Asteroidea, (b) the brittle star of class Ophiuroidea, (c) the sea urchins of class Echinoidea, (d) the sea lilies belonging to class Crinoidea, and (e) sea cucumbers, representing class Holothuroidea. (credit a: modification of work by Adrian Pingstone; credit b: modification of work by Joshua Ganderson; credit c: modification of work by Samuel Chow; credit d: modification of work by Sarah Depper; credit e: modification of work by Ed Bierman)

Phylum chordata

Animals in the phylum Chordata    share four key features that appear at some stage of their development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. In some groups, some of these traits are present only during embryonic development. In addition to containing vertebrate classes, the phylum Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets). Most tunicates live on the ocean floor and are suspension feeders. Lancelets are suspension feeders that feed on phytoplankton and other microorganisms.

Section summary

Echinoderms are deuterostomic marine organisms. This phylum of animals bears a calcareous endoskeleton composed of ossicles. These animals also have spiny skin. Echinoderms possess water-based circulatory systems. A pore termed the madreporite is the point of entry and exit for water into the water vascular system. Osmoregulation is carried out by specialized cells known as podocytes.

The characteristic features of Chordata are a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets), together with the vertebrates in Vertebrata. Most tunicates live on the ocean floor and are suspension feeders. Lancelets are suspension feeders that feed on phytoplankton and other microorganisms.

Questions & Answers

What is biodiversity
Chati Reply
the diversity of plants and animals life in a particula habitat
Harry
what is glycolisis
David Reply
glycolisis is the breakdown of glucose
Yazi
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Hope Reply
What is biodiversity
Chati
what is taxonomy
Patience Reply
Taxonomy is a branch of biology that deals with the description, identification, nomenclature, and classification of organisms
Farco
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John
nomenclature is the scientific naming of organisms
Bigenis
state the structural differences between the termites
Massa
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venius Reply
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Trox Reply
how are proteins digested
Kaka
guys what is locomotion?
Misheal Reply
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Mohamed Reply
no idea
Benard
Anatomy is the branch of science that deals with the study of internal and external structures of an organism
Bigenis
Anatomy is the branch of science that deals with the study of the internal structure of an organism
Nana
what is locomotion?
Misheal
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John
Locomotion may simply mean the movement of an organism from one point to another without permanent displacement of the organidm it'self
Bigenis
simply, its the ability to move
MissMeriiit
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Misheal
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Dickens
locomotion as an art student is the ability to move from on place to another
John
muscles that are concerned with locomotion
John
Anatomy deals with the study of internal structures of an organism
Osei
The ability of cells or organisms to move and propel itself from place to place. supplement. locomotion in biology pertains to the various movements of organisms (single-celled or multicellular organisms) to propel themselves from one place to another.
garnhial
Anatomy is the branch of biology concerned with structure of organisms and their parts. Anatomy is a branch of natural science which deals with the structure organization of living things - human anatomy is one of the essential basic sciences that are applied in medicine
garnhial
what is multicellular organisms
Massa
multicellular organisms these are living things which have more than one cell
John
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Julius Reply
What's the function of epiglottis
Ugo Reply
What Is The Other Name For Intestinal Juice?
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rick Reply
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prokaryotic and eukaryotic
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prokaryotic cell and eukaryotic cell
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globin
Joelia
Globin
globulins
EZRA
globulins
SASMITA
globulins
Grace
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Emmanuel Reply
Parasitic movement is a problem for all of us. So is its companion, parasitic tension. Parasitic movement is the excess contraction of muscles that you don't actually need to complete an action.
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absorption may simply mean utilization of food in the body
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Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
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