Chordata
Subject: Biology
Overview
This note contains detail information about Chordata along with its diagnostic features.The notochord is an elastic solid, skeletal rod lies above the alimentary canal and below dorsal tubular nerve chord. It serves as the primitive internal skeleton.Chordata
- Chorde: a string on rod
- ata: bearing
Chordata is bilaterally symmetrical, triploblastic, coelomates having a supporting skeletal rod i.e. notochord, a nerve chord, pharyngeal gill slits which may persist change or disappear in the adult. Phylum Chordata was created by Belfaur.
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Diagnostic characteristics of phylum Chordata
Presence of notochord
The notochord is an elastic solid, skeletal rod lies above the alimentary canal and below dorsal tubular nerve chord. It serves as the primitive internal skeleton.
Dorsal tubular nerve chord
It is the hollow fluid-filled tubular structure formed by infolding of ectoderm, lies above notochord and exterior to coelom.
Pharyngeal gill slits
These are paired gill slits which arise from the pharynx to exterior.
Beside these, ventral heart, close circulation, RBC, post-anal tail hepatic portal system etc are very important features of chordates. On the basis of position of notochord, phylum Chordata is divided into 4 subphylum;
- Hemichordata: Notochord at heart only. Eg;Balangle
- Urochordata: Notochord at tail only. Eg; Hardmania
- Cephalochordata: Notochord extends from head to tail. Eg; Branchiostoma
- Vertebrata or Craniata: Notochord is found in the embryonic stage and replaced by the vertebral column in the adult. Brain encloses within the cranium.
| S.N | Chondricthyes [Gr.Chondros:cartilage ichythes: fishes] | Osteicthyes [Gr. Osteon: bony icthyes:fishes] | |
| 1 | Habitat | Mostly marine | Mostly fresh water |
| 2 | Endoskeleton | Cartilaginous | Bony |
| 3 | Mouth | Ventral | Terminal |
| 4 | External nerve | Ventral | Dorsal |
| 5 | Gills | 5-7 pairs | 4 pairs |
| 6 | Operculum | absent | present |
| 7 | Scales | Placoid(Non-volatile) | Cycloid (Visible) |
| 8 | Caudal fin | Heterocercal | Homocercal |
| 9 | Cloaca | Present | Absent (anus present) |
| 10 | Spiral valve | Present in intestine | Absent in intestine |
| 11 | Excretion | Urea | Ammonia |
| 12 | Swim | Absent | Present |
| 13 | Bladder fins | Paired | Paired and unpaired |
| 14 | Fertilization | Internalm Eg; Torpido | External Eg; Labeo |
Things to remember
- Chordata are bilaterally symmetrical, triploblastic, coelomates having a supporting skeletal rod i.e. notochord, a nerve chord, pharyngeal gill slits which may persist change or disappear in adult.
- Notochord is an elastic solid, skeletal rod lies above alimentary canal and below dorsal tubular nerve chord.
- Hemichordata: Notochord at heart only. Eg;Balangle
- Vertebrata or Craniata: Notochord is found in embryonic stage and replaced by vertebral column in adult. Brain encloses within cranium.
- It includes every relationship which established among the people.
- There can be more than one community in a society. Community smaller than society.
- It is a network of social relationships which cannot see or touched.
- common interests and common objectives are not necessary for society.
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