Difference Between Octopus and Jellyfish

Octopus vs Jellyfish

The difference between octopus and jellyfish can be explained in terms of their anatomy and physiology. Octopus and jellyfish are aquatic invertebrates. Because of the different anatomy and physiology of these two organisms, they are categorized under different phyla. Octopus is categorized under Phylum Mollusca while Jellyfish is categorized under Phylum Cnidaria. The main similar feature of octopus and jelly fish is the presence of soft body. In addition, both organisms are carnivores and have very primitive body structures without advanced organ systems like in vertebrates. Except for the few similar features that they share, the octopus and jelly fish are two different organisms with different anatomy and physiology. Let us look at those specific features that differentiates one from the other here in detail.

What is Octopus?

Octopus is categorized under Phylum Mollusca, Class Cephalopoda and is found in oceans throughout the world. Other than octopus, squids and nautiluses are also considered as cephalopods. Octopuses are predators and have closed circulatory systems, which is unique to Cephalopods. In addition, they have a relatively large brain and highly developed nervous system. Their foot is modified into eight arms with adhesive structures or suction cups that are used to capture the prey. After capturing the prey with their arms, they bite the prey with their strong, beak-like jaws.

When octopuses are threatened, they expel a dark cloudy liquid, which helps them to avoid and confuse predators. Unlike the other mollusks (except squid), some octopuses are capable of changing their skin color and texture to blend with the background or to communicate with other octopuses.

Difference Between Octopus and Jellyfish

What is Jellyfish?

Jellyfish is an acoelomate with very primitive body structure and is found in coastal waters in tropical and temperate seas. They belong to Phylum Cnidaria, which also include hydroids, corals, and sea anemones. Cnidarians have two body forms; polyp and medusa. Some species occur only as polyp, whereas some occur only as medusa. But most species have both these form s in their life cycle. Jellyfish shows radial symmetry and the body has tissues, but no organs. Medusa form resembles the jellyfish. Class Scyphozoa, Class Cubozoa, and Class Staurozoa are mainly composed of various jellyfish species.

There are about 300 species of jellyfish in the world. The box jellyfish is the largest and considered as one of the deadliest organisms on earth. Jellyfish is carnivorous and feed on small planktons and fish. These creatures have incomplete digestive system, where mouth opens into a simple digestive sac. Mouth opening is surrounded by tentacles armed with nematocysts, which are used to kill their prey.

 Octopus vs Jellyfish

What is the difference between Octopus and Jellyfish?

• Phylum:

• Octopus belongs to Phylum Mollusca.

• Jellyfish belongs to Phylum Cnidaria.

• Presence of Coelom:

• Octopus is coelomates (True coelom is present).

• Jellyfish is acoelomates (True coelom is absent).

• Digestive system:

• Octopus has complete digestive tract with both mouth and anus.

• Jellyfish has incomplete digestive tract with only mouth.

• Nervous system:

• Octopus has a large brain and well-developed nervous system.

• Jellyfish has a very primitive nerve net.

• Presence of nematocysts:

• Jellyfish has nematocysts; a specialized cell.

• Octopus has no nematocysts.

• Presence of tentacles:

• Octopus has eight tentacles with suction pads to capture prey.

• Jellyfish has few tentacles around its mouth with nematocysts to capture prey.

• Circulatory system:

• Closed circulatory system is present in octopus.

• No circulatory system is found in jellyfish.

• Eyes:

• Octopus has well-developed eyes.

• No eyes are found in jellyfish.

• Muscles and a jaw:

• Muscles and a jaw are found in an octopus.

• Muscles and a jaw are not found in a jellyfish.


Images Courtesy:

  1. Octopus by DreamOfShadows (CC BY 2.0)
  2. Jellyfish by Anastasia Shesterinina (CC BY-SA 3.0)