[Untitled photograph of a giraffe]. (n.d.). Retrieved February 20, 2014, from
http://wakpaper.com/large/Giraffes_wallpapers_331.jpg
Elephants. (n.d.). Retrieved February 25, 2014,
from http://www.wildaid.org/elephants
• Notochord - provides a dorsal, flexible rod that functions as a support.
Replaced by bone during development in most chordates.
• Dorsal hollow nerve cord - forms the basis for the nervous system. In
some chordates, the nerve cord becomes the brain and spinal cord.
• Pharyngeal gill slits (pharyngeal pouches) - provide channels across the
pharynx to the outside of the body. In some, the slits become gills for
oxygen exchange or filter feeding, while in others, they disappear during
embryonic development.
• Muscular tail (post-anal tail) - extends beyond the digestive tract. In
many, such as humans, the tail is lost during embryonic development.
Diversity of chordates.
Flowchart. (n.d.). Retrieved February 25, 2014,
from
http://bioweb.uwlax.edu/bio203/s2012/staude
r_abig/classification.htm
Cephalochordates, commonly called amphioxus or lancelets, are marine invertebrate and
a very small branch of the animal kingdom. It’s a phylum of about 25 different species of
animals. They inhabit mostly shallow tropical and temperate oceans.
• Shape- slender, laterally compressed, translucent animals about
5 to 7 cm in length.
• Parts of the organism- Small, eel-like having a notochord, or
dorsal stiffening rod, as the chief internal skeletal support at
some stage of their development.
Alligator and fetus – Chapter
35. (n.d.). Retrieved February
25, 2014, from
http://highered.mcgrawhill.com/sites/0073532223/st
udent_view0/chapter35/imag
e_powerpoint_for_students.htm
l
There are more than 20 species of fish-like marine chordates
About 25 species inhabiting shallow tropical and temperate oceans
Cephalochordates are a very small branch of the animal kingdom.
• How nutrients are obtain: Water is drawn in to the
mouth by the beating of the cilia located on the wheel
organ(a set of ridges lying inside the mouth). Water
gets filtered by the oral cirri(slender projections that
surround the opening of the mouth). It then passes
through the gill slits. These gill slits are enclosed by
metapleural(fin-like folds) folds of the body wall, to
form a body cavity known as the atrium.
•
Food particles in the water are trapped by mucus,
while water goes through the slits and out of the atrium
through the atriopore, located towards the posterior
end.
• The rest of the digestive system is fairly simple: a
pouch or hepatic caecum secretes digestive enzymes,
and actual digestion takes place in a specialized part
of the intestine known as the iliocolonic ring.
• Mechanisms of Metabolism: Cephalochordates have a
well-developed circulatory system and a simple
excretory system composed of
paired nephridium(nephridia for plural).
Sexes are separate, both male and female have multiple paired gonads(organ
that makes gametes). Eggs are fertilized externally & develop into fish-like
larvae.
Lancelet sexes are separate and asexual reproduction does not occur.
Eggs and sperms are sperm are shed directly into the water, where fertilization
occurs.
• Comparison between cephalochordate and vertebrates
genomes has allowed us to postulate a picture for the genome
of the last common ancestor of all chordates.
• Their significance has to do with their place in evolution, as
invertebrates transitioned to vertebrates providing clues for the
history of human lineage. Aleksandr Kowalevsky first shown the
connection in 1867, with embryological evidence that was
influential in establishing that evolution has in fact occurred.
More recently, the relationship has been well-supported by
gene sequence comparisons. Lancelets have a structure that
illustrates the characteristic features of chordates in simple
form.
Since cephalochordates have no hard parts, their fossil record are
extremely sparse.
three unique features of chordates found in all of them are:
•
the notochord, composed of gelatinous tissue and bound by a tough
membrane;
•
a tubular nerve cord (or spinal cord), located above the notochord;
•
gill slits leading into the pharynx, or anterior part of the digestive
tract (the throat, in higher vertebrates).
In addition, all have blood contained in vessels, and the tunicates and
vertebrates have a ventrally located heart.
All have a post-anal tail, that is, an extension beyond the anus of the
notochord or backbone and of the body-wall musculature, containing no
internal organs.
Characteristics of Chordates: tunicates and salps
(salpa)
Diversity: 1250 species of marine animals
immobile as adults
Only the larvae having a notochord and nerve chord
Body has more than two cell layers and includes tissues and organs.
Do not feed and have a poorly developed gut
Body wholly enclosed in a 'tunic' of secreted protein and cellulose-like material.
Are hermaphroditic, normally with only one ovary and testis. Can reproduce
sexually or asexually.
All are filter feeders.
Live in marine environments.
Has a nervous system composed of a anterior ganglion from which individual nerves issue.
Has no excretory organs.
Has a distinct larval stage.
• Reproduce sexually
• Features: Vertebral column - the notochord is replaced during
embryonic development by a vertebral column, head distinct and well-differentiated head with three pairs of welldeveloped sensory organs, neural crest - a unique group of
embryonic cells and they participate in the development of
many different structures, internal organs - liver, kidneys,
and endocrine glands. All have a heart and a closed
circulatory system, endoskeleton - made of cartilage or bone
• Fishes, amphibians, reptiles, birds, and mammals
• Fishes:
• 5 characterists: vertebral column of bone or cartilage, jaws, paired
appendages, internal gills, and a closed circulatory system.
• Sharks, rays, and skates are cartilaginous fishes. Bony fish:
Actinopterygii (ray-finned) or Sarcopterygiin (lobe-finned fishes)
• Amphibians:
• 5 features: legs, lungs, cutaneous respiration, pulmonary veins,
and a partially divided heart.
• Anura (frogs and toads) lack tails as adults, many have a larval
tadpole stage. Caudata (salamanders) have tails as adults and
larvae similar to the adult form. Apoda (caecilians) are legless.
• Mammals:
• Characteristics: hair, mammary glands - provide milk to feed
their young, and other characteristics - like being
endothermic.
• Evolved from therapsids (synapsids - reptiles) and reached
maximum diversity about 15 mya.
• Modern mammals - 3 groups: monotremes (lay shelled
eggs), marsupials (an embryo completes development in a
pouch), and placental mammals (produce a placenta in the
uterus to nourish the embryo).
• Vertebrates are both predator and prey.
• Inc, A. (2012, january 8). Tunactes. Retrieved from Ocean Observations:
http://oceanobservations.blogspot.com/2012/01/tunicates.html
• Britannica, E. (2014). Cephalochordate. Retrieved from The Encyclopedia
Britannica:
http://www.britannica.com/EBchecked/topic/103023/cephalochordate
• Chen, J.-Y. D.-Q. (1995). A Possible Early Cambrian Chordate. Nature
377:720-722.
• Encyclopedia, T. C. (2012). The Columbia Electronic Encyclopedia, Sixth
Edition. Retrieved from
http://www.infoplease.com/encyclopedia/science/chordata.html
• Raven, P. H., Johnson, G. B., Mason, K. A., Losos, J. B., & Singer, S. R. (2011).
Biology, Ninth Edition. The McGraw-Hill Companies, Inc.
• Ruppert, E. E., & Bames, R. (1994). Invertebrate Zoology, Sixth Edition.
Saunders College Publishing, Fort Worth.