DEFINITION
- Animals with notochord in some stage of their life cycle are known as chordates whereas those which do not develop are called as non-chordates.
- Segmentation is an architectural body plan in which an organism is built by a series of segments known as metamers.
- The segments can be both internally and externally.
- Homolecithal or Isolecithal: In this type, the quantity of yolk is very less and it is uniformly distributed all over the egg cytoplasm. For example, eggs of echinoderms.
- Heterolecithal: In these types of eggs, yolk is not evenly distributed in cytoplasm. They may be telolecithal, meiolecithal, centrolecithal.
They are classified on the basis of the following points:
The structural organization (body design)
Body symmetry: a) Asymmetrical (irregular shape)
b) Symmetrical (regular shape):
1. Bilateral symmetry
2. Radial symmetry
3. Spherical symmetry
Presence or absence of notochord: The animals having notochord develop a skeleton as in the vertebrates and the ones without having notochord have no skeleton as in invertebrates.
Presence or absence of coelom:
Coelomates: Each plan consists of three cell layers: endoderm, mesoderm and ectoderm.
Acoelomates: They have no cavity other than the gut. Also called solid worms.
Pseudocoelomates: They have a body cavity that is not completely lined with mesoderm.
Radially symmetrical, diploblastic multicellular animals with a tissue grade of organisation.
Aquatic, freshwater or marine solitary or colonial forms which may be free swimming or sedentary.
Locomotion and food capturing: tentacles.
Cnidoblasts, nematocysts or stinging cells used for offence and defence.
Coelom is absent. Hence, coelenterates are acoelomate animals
Reproduction is asexually or sexually.
For example, Hydra, sea anemone, jellyfish.
- Common roundworms causes Ascariasis.
- Ascaris lumbricoides is the giant roundworm of humans, growing to a length of up to 35 cm.
- Most often, eggs, or larvae, live in the soil and get into the body when you get them on your hands and then touch your mouth.
- Some can also get into the body through the skin.
They are mostly marine, soft, unsegmented, triploblastic body having bilateral symmetry
Developed coelom and possess notochord only in the embryonic stage
The body has three distinct parts i.e., proboscis, collar and trunk
Reproduction: Sexual
For examples, Balanoglossus, Herdmania, Amphioxus
- The notochord provides skeletal support, gives the phylum its name, and develops into the vertebral column in vertebrates.
- The dorsal hollow nerve cord develops into the central nervous system: the brain and spine.
- Pharyngeal slits are openings in the pharynx that develop into gill arches in bony fish and into the jaw and inner ear in terrestrial animals.
- The post-anal tail is a skeletal extension of the posterior end of the body, being absent in humans and apes, although present during embryonic development.
Urochordata
- Possesses a Notochord, a hollow nerve cord and a post anal tail.
- Body has more than two cell layers and includes tissues and organs.
- Has a U shaped gut.
- Body has no coelomic body cavity.
- Body wholly enclosed in a 'tunic' of secreted protein and cellulose-like material.
- Are hermaphroditic, normally with only one ovary and testis.
- Has a nervous system composed of a anterior ganglion from which individual nerves issue.
- Has no excretory organs.
- Has a distinct larval stage.
- All are filter feeders.
- Live in marine environments.
- Body is fish-like and is useful for burrowing and swimming.
- It has a head and shows a tail.
- Appendages are absent.
- Dorsal, caudal and ventral fins are present.
- Body- wall shows one- cell thick, non-ciliated epidermis, dermis, connective tissue, striated muscle and parietal peritoneum.
- Notochord extends from the anterior end to posterior end.
- They have a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail.
- Vertebrates are further differentiated from chordates by their vertebral column, which forms when their notochord develops into the column of bony vertebrae separated by discs.
- Vertebrates are the only chordates that have a brain as part of their central nervous system.
- These fishes have teeth-like scales, denticles, which include the sharks, rays, skates and ratfishes.
- Their mouth is usually located ventrally and they were the first fishes to have paired fins (pectoral and pelvic fins) for more efficient swimming.
- They have 5 to 7 gill slits per side and no swim bladder.
- The largest Chondrichthyes are the plankton feeders.
- Skin with mucus gland. Paired fins made of rays and spines, or lobed fins lacking the rays and spines.
- Various types of scales (ctenoid, ganoid, or cycloid).
- Marine and fresh water species.
- Gills used for respiration.
- External fertilization: spawning, oviparous.
- No external ears.
- No eyes.
- Skeleton made of bone.
- Lateral line.
- Two chambered heart. Operculum covering the gills. Brain with large optic lobes and cerebellum.
- For example, Labeo, Hippocampus.
Hard, horny scaly skin, four legs and breathe with lungs.
Three chambered heart (crocodiles have four chambered heart), breathe through lungs, cold blooded or poikilothermal.
Eggs have leathery shell.
Unisexual, oviparous, fertilization is internal.
For example, turtle, chameleon, king cobra, flying lizard, house wall lizard etc.
- In birds, as the fertilized egg or zygote travels down the oviduct, several layers of yolk and protective coverings are deposited around it by the wall of oviduct and uterus.
- The hard shell is the outermost protective layer.
- These shelled eggs are laid by the birds.
- The development of chick takes place inside the egg shell.
Gives birth to young ones except for Australian spiny ant-eater and duck-billed platypus which lay eggs.
Four chambered heart, breathe through lungs, warm-blooded or homeothermic.
Muscular diaphragm separating the thorax and abdomen internally.
Mammary glands secrete milk, pair of external ears and external testes contained in a scrotum.
- For example, humans, cats, dogs, mice, rabbits, cows, lions, elephants, kangaroos, whales, seals, dolphins, porpoises etc.
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