Protochordata

The organisms belonging to the Protochordata are generally known as the lower chordates. They don’t form a “proper” taxonomic group and are only classified as such for convenience purposes. However, they do form a major group of Chordata. They are also known as Acraniata because they lack a true skull. They are divided into two subphyla- Urochordata, Cephalochordata.

Characteristics of Protochordata

1. They are generally found in marine water.
2. Their body is bilaterally symmetrical, triploblastic, and coelomated.
3. At a certain stage of their lives, their body develops a long, rod-like structure for support called the notochord.
4. They exhibit organ system level of organization.

E.g., Herdmania, Amphioxus.

Classifications of Protochordata

Urochordata or Tunicata

• They are found in the marine environment.
• They are sessile and filter-feeders.
• They are also known as tunicates because their body is surrounded by a leathery sheath composed of tunicin (cellulose).
• The notochord appears in the larval stage in the tail of the larva and disappears in the adult. This is known as retrogressive metamorphosis.
• The neural tube in the larva is replaced by a dorsal ganglion in the adults.
• Respiration occurs through gills.
• They have an open circulatory system.
• The excretory organs are absent.
• They reproduce asexually by budding.

E.g., Herdmania, Selpa

Cephalochordata

• They are marine and filter-feeders.
• The notochords remain throughout life and extend up to the head region.
• The nerve cord and the tail also remain throughout life.
• Solenocytes are the excretory organs.
• They respire through gills which open in the atrium.
• The body wall comprises myotomes.

E.g., Amphioxus

Also check: Blood Vascular System of Branchiostoma

Learn more in detail about Protochordata, its features, classifications and other related topics at BYJU’S Biology.

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