Salient features of chordates?
The salient features of chordates include several key characteristics that appear at some stage in their development. These features are fundamental to defining the phylum Chordata:
- Notochord: A flexible, rod-like structure providing skeletal support. Present in all chordates during embryonic development; persists in adults of some species like lancelets (Cephalochordata), but is replaced by a vertebral column in vertebrates.
- Dorsal Hollow Nerve Cord: Located dorsally to the notochord, this nerve cord is hollow and tubular. Develops into the brain and spinal cord in most chordates, providing a central nervous system.
- Pharyngeal Slits (Gill Slits): Openings in the pharynx that allow water to exit during feeding in aquatic species. In fish, these slits become gill arches; in terrestrial animals, they often develop into jaw and inner ear structures during embryogenesis.
- Post-anal Tail: An extension beyond the anus, providing locomotion in aquatic species. Absent in many adult chordates but present during embryonic development[1][2][3].
Additional characteristics common among chordates include: Bilateral Symmetry, Triploblastic Body, True Coelom and Segmentation.
Difference between Chordates and non chordates
| Characteristics | Chordates | Non-Chordates |
|---|---|---|
| Notochord | Present (at least in one stage) | Absent |
| Nerve Cord | Dorsal hollow nerve cord | Ventral nerve cord, often without a brain |
| Body Symmetry | Bilateral symmetry | Bilateral, radial, or asymmetrical |
| Body Cavity | True coelomates | Acoelomate, pseudocoelomate, or coelomate |
| Circulatory System | Closed circulatory system | Open or closed circulatory system or absent |
| Respiratory System | Gills or lungs in vertebrates | Gills, trachea |
Characters of Protochordates:
Protochordates, also known as lower chordates or acraniates, are an informal group within the phylum Chordata. They are divided into three main sub-phyla: Hemichordata, Urochordata, and Cephalochordata. Here are the key characteristics of protochordates:
- Notochord: Many protochordates have a notochord at some stage of their life. In Cephalochordata, it extends from head to tail and persists throughout life, while in Urochordata, it is usually confined to the larval tail.
- Body Structure: They have a bilaterally symmetrical, triploblastic body with a coelom (true body cavity).
- Dorsal Hollow Nerve Cord: Protochordates have a primitive dorsal nerve cord that is hollow and tubular, though it might not be well-developed compared to vertebrates.
- Pharyngeal Slits: Present as gill slits in the pharynx, facilitating water circulation for respiration in aquatic environments.
- Post-anal Tail: Commonly found in protochordates, providing support and balance.
- Circulatory System: Typically closed, with a ventral heart and blood vessels.
- Feeding and Living Habitats: Most are marine and have various feeding methods; some are filter-feeders.
- Examples: Notable examples include Amphioxus (Cephalochordata), Balanoglossus (Hemichordata), and Salpa (Urochordata).
