Difference Between Acrania and Craniata

Key Difference – Acrania vs Craniata
 

Both Acrania and Craniata belong to the phylum Chordata. The key difference between Acrania and Craniata is based on the presence or the absence of head or skull in the particular organism. The organisms belonging to the subphylum Acrania do not have a cranium or a distinguished head structure. In contrast, organisms belonging to subphylum Craniata possess a cranium.

The phylum Chordata possess characteristic features such as the nerve cord, notochord, and the pharyngeal slits.

CONTENTS

1. Overview and Key Difference
2. What is Acrania
3. What is Craniata
4. Similarities Between Acrania and Craniata
5. Side by Side Comparison – Acrania vs Craniata in Tabular Form
6. Summary

What is Acrania?

Subphylum Acrania belongs to the Phylum Chordata. Organisms belonging to Acrania do not possess a cranium. Therefore, they lack the brain, skull, jaws and eyes and auditory organs. This makes the organisms belonging to the subphylum Acrania as the most primitive chordates. They possess a dorsal, and a hollow nerve cord and their notochord extends throughout the entire length of the body. The pharyngeal gill slits are a lot in number, and they are open to the atrium.

Figure 01: Acrania – Branchiostoma

This subphylum (Acrania) has subclasses Hemichordata, Urochordata and Cephalochordata. The species belonging to the subphylum Acrania are mostly found in marine environments in the coastal areas. The structural and functional aspects of the organism enable the identification Acranial species. Their nervous system consists of a spinal cord and nerves deviating from the central spinal cord. There is a sac-like structure that houses the sensory cells. And they possess a ventral mouth and a slit surrounded by supporting rods. The pharynx is prominent in subphyla Acrania, and it ends up in a hypopharyngeal groove. Branchiostoma and Asymmetron are examples for Acrania.

What is Craniata?

Subphylum Craniata of the phylum Chordata comprises of organisms that possess a prominent cranium. Thus, these organisms possess a brain, skull and jaws. This subphylum is also known as the subphylum Vertebrata. Species belonging to Craniata has a well-developed vertebral column with 10 – 12 pairs of cranial nerves and the brain. They all possess an endoskeleton, and the notochord does not extend beyond the brain.

Figure 02: Craniata

Another unique feature of the subphylum Craniata is the presence of chambered hearts. The number of chambers may differ from class to class. The blood vessels and blood corpuscles are present, and a hepatic portal system is observed. They also possess excretory organs such as the kidneys. Petromyzon, frog, fish, etc. are examples of Craniata.

What are the Similarities Between Acrania and Craniata?

• Both Acrania and Craniata are subphyla belonging to Phylum Chordata.
• Both Acrania and Craniata have a dorsal nerve cord.

What is the Difference Between Acrania and Craniata?

Summary – Acrania vs Craniata

Subphyla Acrania and Craniata belong to the phylum Chordata. They distinguish between the presence and absence of the cranium or the head. The subphylum Acrania does not possess the cranium, thus lack the brain, skull, jaws and organs such as auditory organs. The subphyla Craniata possess a distinct cranium. Therefore, they show the distinct cranial structures. This is the difference between Acrania and Craniata.

Reference:

1. “Subphylum Vertebrate (Craniata) | Phylum Chordata.” Biology Discussion, 22 July 2016. Available here
2. “Classification of Subphy­LumAcrania | Zoology.” Zoology Notes, 11 Jan. 2017. Available here 

Image Courtesy:

1. ‘Branchiostoma lanceolatum’By © Hans Hillewaert, (CC BY-SA 4.0) via Commons Wikimedia  
2. ‘Pacific hagfish Myxine’ (Public Domain) via Commons Wikimedia 

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