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The post-anal tail    is a posterior elongation of the body extending beyond the anus. The tail contains skeletal elements and muscles, which provide a source of locomotion in aquatic species, such as fishes. In some terrestrial vertebrates, the tail may also function in balance, locomotion, courting, and signaling when danger is near. In many species, the tail is absent or reduced; for example, in apes, including humans, it is present in the embryo, but reduced in size and nonfunctional in adults.

Art connection

The illustration shows a fish-shaped chordate. A long, thin dorsal hollow nerve cord runs the length of the chordate, along the top. Immediately beneath the nerve cord is a notochord that also runs the length of the organism. Beneath the notochord, pharyngeal slits cut diagonally into tissue toward the front of the organism. A post-anal tail occurs at the rear.
In chordates, four common features appear at some point in development: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. The anatomy of a cephalochordate shown here illustrates all of these features.

Which of the following statements about common features of chordates is true?

  1. The dorsal hollow nerve cord is part of the chordate central nervous system.
  2. In vertebrate fishes, the pharyngeal slits become the gills.
  3. Humans are not chordates because humans do not have a tail.
  4. Vertebrates do not have a notochord at any point in their development; instead, they have a vertebral column.

Invertebrate chordates

In addition to the vertebrates, the phylum Chordata contains two clades of invertebrates: Urochordata    (tunicates) and Cephalochordata    (lancelets). Members of these groups possess the four distinctive features of chordates at some point during their development.

The tunicates ( [link] ) are also called sea squirts. The name tunicate derives from the cellulose-like carbohydrate material, called the tunic, which covers the outer body. Although tunicates are classified as chordates, the adult forms are much modified in body plan and do not have a notochord, a dorsal hollow nerve cord, or a post-anal tail, although they do have pharyngeal slits. The larval form possesses all four structures. Most tunicates are hermaphrodites. Tunicate larvae hatch from eggs inside the adult tunicate’s body. After hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location. It then attaches by the head to the substrate and undergoes metamorphosis into the adult form, at which point the notochord, nerve cord, and tail disappear.

Photo a shows tunicates, which are sponge-like in appearance and have a few holes along the surface. Illustration b shows the tunicate larval stage, which resembles a tadpole, with a post-anal tail at the narrow end. A dorsal hollow nerve cord runs along the upper back, and a notochord runs beneath the nerve cord. The digestive tract starts with the mouth at the front of the animal connected to a stomach. Above the stomach is the anus. The pharyngeal slits, which are located between the stomach and mouth, are connected to an atrial opening at the top of the body. Illustration c shows an adult tunicate, which resembles a tree stump anchored to the bottom. Water enters through the mouth at the top of the body and passes through the pharyngeal slits, where it is filtered. Water then exits through another opening at the side of the body. The heart, stomach, and gonad are tucked beneath the pharyngeal slits.
(a) This photograph shows a colony of the tunicate Botrylloides violaceus . In the (b) larval stage, the tunicate can swim freely until it attaches to a substrate to become (c) an adult. (credit a: modification of work by Dr. Dwayne Meadows, NOAA/NMFS/OPR)

Most tunicates live a sessile existence in shallow ocean waters and are suspension feeders. The primary foods of tunicates are plankton and detritus. Seawater enters the tunicate’s body through its incurrent siphon. Suspended material is filtered out of this water by a mucus net (pharyngeal slits) and is passed into the intestine through the action of cilia. The anus empties into the excurrent siphon, which expels wastes and water.

Lancelets possess a notochord, dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail in the adult stage ( [link] ). The notochord extends into the head, which gives the subphylum its name (Cephalochordata). Extinct fossils of this subphylum date to the middle of the Cambrian period (540–488 mya).The living forms, the lancelets, are named for their blade-like shape. Lancelets are only a few centimeters long and are usually found buried in sand at the bottom of warm temperate and tropical seas. Like tunicates, they are suspension feeders.

The illustration shows a lancelet with the head protruding from the sand, and the rest of the body buried. On the head, tentacles surround the mouth. The mouth leads to the digestive tract. The anus is located just before the post-anal tail. The pharyngeal slits are next to the atrium, which empties into the atriopore. The body has segmented muscles running along it from top to bottom.
Adult lancelets retain the four key features of chordates: a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.

Section summary

Echinoderms are deuterostome marine organisms. This phylum of animals bear a calcareous endoskeleton composed of ossicles covered by a spiny skin. Echinoderms possess a water-based circulatory system. The madreporite is the point of entry and exit for water for the water vascular system.

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. Most tunicates live on the ocean floor and are suspension feeders. Lancelets are suspension feeders that feed on phytoplankton and other microorganisms.

Art connections

[link] Which of the following statements about common features of chordates is true?

  1. The dorsal hollow nerve cord is part of the chordate central nervous system.
  2. In vertebrate fishes, the pharyngeal slits become the gills.
  3. Humans are not chordates because humans do not have a tail.
  4. Vertebrates do not have a notochord at any point in their development; instead, they have a vertebral column.

[link] A

Questions & Answers

where we get a research paper on Nano chemistry....?
Maira Reply
nanopartical of organic/inorganic / physical chemistry , pdf / thesis / review
Ali
what are the products of Nano chemistry?
Maira Reply
There are lots of products of nano chemistry... Like nano coatings.....carbon fiber.. And lots of others..
learn
Even nanotechnology is pretty much all about chemistry... Its the chemistry on quantum or atomic level
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da
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Bhagvanji
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Giriraj
Preparation and Applications of Nanomaterial for Drug Delivery
Hafiz Reply
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da
Application of nanotechnology in medicine
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RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
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Professor
I think
Professor
Nasa has use it in the 60's, copper as water purification in the moon travel.
Alexandre
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Alexandre
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Brian Reply
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Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
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What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
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what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
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Anam
Any one who tell me about Preparation and application of Nanomaterial for drug Delivery
Hafiz
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
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Renato
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why we need to study biomolecules, molecular biology in nanotechnology?
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Kyle
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Adin
why?
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biomolecules are e building blocks of every organics and inorganic materials.
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Source:  OpenStax, Bmcc 103 - concepts of biology. OpenStax CNX. Aug 06, 2015 Download for free at https://legacy.cnx.org/content/col11855/1.2
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