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Concept in action

View this video to explore a sea star’s body plan up close, watch one move across the sea floor, and see it devour a mussel.

Brittle stars have long, thin arms that do not contain any organs. Sea urchins and sand dollars do not have arms but are hemispherical or flattened with five rows of tube feet, which help them in slow movement. Sea lilies and feather stars are stalked suspension feeders. Sea cucumbers are soft-bodied and elongate with five rows of tube feet and a series of tube feet around the mouth that are modified into tentacles used in feeding.

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 in class Asteroidea, (b) the brittle star in 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)

Chordates

The majority of species in the phylum Chordata are found in the subphylum Vertebrata, which include many species with which we are familiar. The vertebrates contain more than 60,000 described species, divided into major groupings of the lampreys, fishes, amphibians, reptiles, birds, and mammals.

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 ( [link] ). In certain groups, some of these traits are present only during embryonic development.

The chordates are named for the notochord    , which is a flexible, rod-shaped structure that is found in the embryonic stage of all chordates and in the adult stage of some chordate species. It is located between the digestive tube and the nerve cord, and provides skeletal support through the length of the body. In some chordates, the notochord acts as the primary axial support of the body throughout the animal’s lifetime. In vertebrates, the notochord is present during embryonic development, at which time it induces the development of the neural tube and serves as a support for the developing embryonic body. The notochord, however, is not found in the postnatal stage of vertebrates; at this point, it has been replaced by the vertebral column    (the spine).

The dorsal hollow nerve cord    is derived from ectoderm that sinks below the surface of the skin and rolls into a hollow tube during development. In chordates, it is located dorsally to the notochord. In contrast, other animal phyla possess solid nerve cords that are located either ventrally or laterally. The nerve cord found in most chordate embryos develops into the brain and spinal cord, which compose the central nervous system.

Pharyngeal slits are openings in the pharynx, the region just posterior to the mouth, that extend to the outside environment. In organisms that live in aquatic environments, pharyngeal slits allow for the exit of water that enters the mouth during feeding. Some invertebrate chordates use the pharyngeal slits to filter food from the water that enters the mouth. In fishes, the pharyngeal slits are modified into gill supports, and in jawed fishes, jaw supports. In tetrapods, the slits are further modified into components of the ear and tonsils, since there is no longer any need for gill supports in these air-breathing animals. Tetrapod means “four-footed,” and this group includes amphibians, reptiles, birds, and mammals. (Birds are considered tetrapods because they evolved from tetrapod ancestors.)

Questions & Answers

what Is taxonom
Don Reply
Taxonom is the the laws and principles guiding the classification of living things either plant 🌿 or animal
Samuel
protein synthesis began with what?
Kesselly Reply
What structures does a plant cell have that an animal cell does not hav
Martin Reply
A plant cell has a cell wall, a large central vacuole, and chloroplasts, which an animal cell does not have.
AI-Robot
what is the function of the cytoskeleton?
Martin
truly. Al-robot
Mark
why is it advantageous for the cell membrane to be fluid in nature?
Martin Reply
The fluid nature of the cell membrane allows for flexibility and dynamic changes in its structure. This allows for the movement of molecules and ions in and out of the cell, as well as the ability to respond to external stimuli. The fluidity of the membrane also allows for the formation of specialized structures such as receptor proteins, which are important for cell-cell communication.
AI-Robot
What is used as a visual marker for successful gene transfer into transgenic animals?
rhonda Reply
Parts of the body involved in homeostasis
Favour Reply
liver
Kirk
A collection of similar-typed cells working together to perform a specific function is called what?
Rachel Reply
tissue
Van
which structure consists of a phospholipid bilayers and it is known as the mosaic model?
Jamar Reply
cell membrane
Abanoub
what is diffusion
Patricia Reply
a passive process of transport
Jamar
Random movement of gas molecule from region of high concentration to a low concentration.
praise
10 difference between male and female reproductive system
Ina Reply
if a phase is omitted ,what will happen to the cell
Ewemoje Reply
discribe advantages and disadvantages of asexual and sexual reproduction
basi Reply
Compared to separate sexes and assuming self-fertilizing is not possible, what might be one advantage and one disadvantage to hermaphroditism?
Gift Reply
is nature of their environment among
basi
cool 😎
Precious
why are the laws of thermodynamics considered laws of nature and not scientific theories
Yolonda Reply
archea were given their own separate domain because they are?
Yolonda
which of the following is a basic component of all of the others?
Yolonda
which of the following organization levels is the least inclusive
Yolonda
which cell feature is absent in bacterial cells
Yolonda
which metric movies the base unit of measurement by one thousandth (0.001)?
Yolonda
What is biology?
Blessing Reply
List the branches of biology
Blessing
List the branches of biology
Blessing
List the branches of biology
Blessing
List the branches of biology
Blessing
Ecology,Anatomy,genetics,biophysics,biochemistry,microbiology and biotechnology.
praise

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Source:  OpenStax, Concepts of biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11487/1.9
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