📘 Phylum Chordata – Animals with Backbone Origins

🔹 General Characteristics:

• Bilateral symmetry, triploblastic, deuterostome, coelomates
• All chordates show these 4 key features at some stage in life:

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✅ 1. Notochord

• A rod-like, semi-rigid structure of vacuolated cells
• Found between gut and dorsal nerve cord
• Present in embryo of all chordates
• Lower chordates: Retain it for life
• Vertebrates: Replaced partly/fully by vertebral column

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✅ 2. Pharyngeal Slits

• Gill slits in the lateral walls of the pharynx

• In:
• 🐟 Fishes → develop into gills
• 🐸 Amphibians → functional in early life
• 🐦🦎🧍Reptiles, Birds & Mammals → modified for other uses

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✅ 3. Tubular Nerve Cord

• Hollow dorsal nerve cord

• Runs above the notochord
• Expands anteriorly to form the brain

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✅ 4. Post-Anal Tail

• Tail located behind the anus
• May remain for life (e.g., fish) or regress in adults (e.g., humans)

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🧬 Classification of Chordates:

🔹 A. Invertebrate Chordates

➤ Subphylum Urochordata

• Notochord & nerve cord only in larval stage
• Example: Sea squirts

➤ Subphylum Cephalochordata

• Notochord persists throughout life
• Example: Amphioxus

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🔹 B. Vertebrates (Backboned Animals)

• Have a vertebral column and cranium
• Divided into two groups:

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🔸 1. Group Pisces (Fishes):

• Have no limbs, only fins

• Includes 3 Classes:

• Cyclostomata (jawless fish)
• Chondrichthyes (cartilaginous fish – e.g., shark)
• Osteichthyes (bony fish – e.g., rohu, trout)

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🔸 2. Remaining Classes of Vertebrates (Tetrapods):

• Will continue in next section 

Related Posts

• Phylum Annelida
• Phylum Arthropoda
• Phylum Echinodermata