Difference Between Hemichordata and Chordata

Main Difference – Hemichordata vs Chordata

Hemichordata and Chordata are two deuterostome phyla. Along with the phylum Echinodermata, Hemichrodata and Chordate belong to a common ancestor. Both hemichordates and chordates are coelomates. Hemichordates are worm-like, marine animals while chordates live in water, land, and air. The main difference between Hemichordata and Chordata is that Hemichordata contains an epidermal nervous system whereas Chordata contains a central nervous system. Chordates contain a dorsal, tubular nerve cord. Both Hemichordata and Chordata contain pharyngeal gill slits. Chordates also contain a post-anal tail. The three classes of hemichordates are Enteropneusta, Pterobranchia, and Planctosphaeroidea. The three subphyla of chordates are Urochordata, Cephalochordata, and Vertebrata.

Key Areas Covered

1. What is Hemichordata
      – Definition, Classification, Habitat, Characteristics
2. What is Chordata
      – Definition, Classification, Habitat, Characteristics
3. What are the Similarities Between Hemichordata and Chordata
      – Outline of Common Features
4. What is the Difference Between Hemichordata and Chordata
      – Comparison of Key Differences

Key Terms: Chordata, Circulatory System, Hemichordata, Nerve Cord, Nervous System, Notochord, Pharyngeal Gill Slits, Post-Anal Tail, Stomochord

What is Hemichordata

Hemichordata refers to a phylum that contains worm-like marine animals with a proboscis as an outgrowth of the pharyngeal wall. The most characteristic feature of hemichordates is the tripartite division of the body. This means their body is divided into three segments: pre-oral lobe, collar, and trunk. Hemichordates have some characters of chordates. They contain pharyngeal gill slits in their collar. The stomochord is a semi-rigid, rod-like structure below the heart of hemichordates. It resembles the notochord of chordates. The circulatory system of hemichordates bears a heart-like, contractile vesicle. It is an open circulatory system with blood vessels and sinuses. The pharyngeal gill slits are used to capture small food particles by non-vertebrate chordates. A hemichordate is shown in figure 1.

Main Difference - Hemichordata vs Chordata

Figure 1: Hemichordate

The three classes of hemichordates are Enteropneusta, Pterobranchia, and Planctosphaeroidea. Enteropneusts are acorn worms that live in shallow water. Pterobranchia contains colonial tube-like worms that live in an externally secreted encasement. Planctosphaeroidea contains planktonic organisms with spherical bodies covered with ciliary bands.

What is Chordata

Chordata refers to an animal phylum that contains a notochord, dorsally situated central nervous system, and gill slits. Chordates can be found in freshwater, marine, and terrestrial habitats. All chordates possess a notochord, dorsal nerve cord, pharyngeal gill slits, and a post-anal tail at some point in their life. The notochord is a rod-like, elongated structure, which occurs dorsal to the gut and ventral to the nerve cord. The nerve cord is a dorsal and hollow. The central nervous system of chordates consists of a brain and a spinal cord. The peripheral nervous system connects the body to the central nervous system. The pharyngeal gill slits occur in the pharyngeal portion of the gut. The notochord, nerve cord, and gill slits are shown in figure 2.

Difference Between Hemichordata and Chordata

Figure 2: Notochord, Nerve Cord, and Gill Slits

The three subphyla of chordates are Urochordata, Cephalochordata, and Vertebrata. Urochordate larva contains the notochord, nerve cord, and the post-anal tail. The adult urochordates are planktonic or sessile. The urochordate body occurs inside a tunic. The body of the Chelochordata is laterally compressed and transparent. Chelochordates present notochord, nerve cord, pharyngeal gill slits, and post-anal tail. In Vertebrata, the notochord is covered by the vertebral column. The vertebral column provides axial support. The anteriorly modified skeleton produces the skull, which protects the brain.

Similarities Between Hemichordata and Chordata

Both Hemichrodata and Chordata belong to a common ancestor.
Both Hemichordata and Chordata are deuterostomes.
Both Hemichordata and Chordata are triploblastic, coelomates.
Both Hemichordata and Chordata possess bilateral symmetry.
Both Hemichordata and Chordata exhibit an organ-system level of organization.
Both Hemichordata and Chordata contain Pharyngeal gill slits.

Definition

Hemichordata: Hemichordata refers to a phylum which contains worm-like marine animals with a proboscis as an outgrowth of the pharyngeal wall.

Chordata: Chordata refers to an animal phylum which contains a notochord, dorsally situated central nervous system, and gill slits.

Habitat

Hemichordata: Hemichordata mostly lives in marine habitats.

Chordata: Chordata lives in marine, freshwater, and terrestrial habitats.

Nervous System

Hemichordata: Hemichordata contains an epidermal nervous system.

Chordata: Chordata contains a central nervous system.

Notochord

Hemichordata: Hemichordata does not contain a notochord. Their nervous tissue is concentrated at the collar.

Chordata: Chordata contains a dorsal, tubular notochord.

Post-anal Tail

Hemichordata: Hemichordata lacks a post-anal tail.

Chordata: Chordata contains a post-anal tail.

Circulatory System

Hemichordata: Hemichordata contains an open circulatory system with dorsal and ventral blood vessels.

Chordata: Chordata contains a closed circulatory system.

Stomochord

Hemichordata: Hemichordata contains a stomochord, which is a semi-rigid, rod-like structure below the heart.

Chordata: Chordata lacks a stomochord.

Blood Pigments

Hemichordata: Hemichordata lacks blood pigments. Therefore, their blood is colorless.

Chordata: Chordata contains blood pigments.

Transportation of Respiratory Gases and Metabolic Wastes

Hemichordata: The transportation of respiratory gases and metabolic wastes occurs through the body wall in Hemichordata.

Chordata: The transportation of respiratory gases and metabolic wastes occurs via blood.

Examples

Hemichrodata: Acorn worms, Rhabdopleura, and Planctosphaertara pelagica are examples of hemichordates.

Chordata: Mammals, birds, reptiles, amphibians, fish, amphioxus, and tunicates are examples of chordates.

Conclusion

Hemichordata and Chordata are two groups of deuterostomes. Hemichordata is a group of marine, worm-like animals. In contrast, chordates live in every habitat on earth. Both hemichordates and chordates consist of a notochord, nerve cord, pharyngeal gill slits, and a post-anal tail. But, hemichordates lack a central nervous system whereas chordates contain a central nervous system. The main difference between Hemichordata and Chordata is their nervous system.

Reference:

1. Introduction to the Hemichordata. Accessed 11 Oct. 2017, Available here.
2.“Tree of Life Chordata.” Tree of Life Web Project, Accessed 11 Oct. 2017, Available here.

Image Courtesy:

1. “Eichelwurm” By User Necrophorus on de.wikipedia – Foto: de:Benutzer:Necrophorus, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=1037045
2. “Image from page 24 of “Chordate anatomy” (1939)” Internet Archive Book Images via Flickr