Question

What is the phylum of octopus?
A) Arthropoda
B) Mollusca
C) Annelida
D) Cnidarian

Answer 1

Hint: Octopus belongs to phylum Mollusca. They have bilateral symmetry, body divided into the foot and visceral mass, and have a triploblastic body. Arthropoda and Annelida include worms. They have segmented bodies. Cnidarians include jellyfishes and hydras.

Complete answer:
The octopus is an aquatic animal which has eight-limbed molluscs of the order Octopoda. They belong to the phylum Mollusca. It is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. It has bilateral symmetry, with two eyes, and a break, with its mouth at the center point of the eight limbs. It has a soft body that it can alter its shape and enables itself to squeeze through small gaps. They have triploblastic eyes. For respiration and locomotion they use siphon which helps them expel a jet of water. Some of the octopuses live in the intertidal zone and others at abyssal depths. Octopuses have a closed circulatory system.
Arthropods and Annelid, both include worms while cnidarians mostly include marine animals such as corals, hydras and jellyfish etc. Arthropod has chitinous exoskeleton, jointed/segmented appendages, a well-developed head and open circulatory system. It includes crabs, spiders, and insects. Annelid includes ringed worms such as ragworms, earthworms, and leeches. Cnidarians have tentacles with stinging cells used to capture prey. They are stinging creatures that’s why they are called Cnidarians.
From the above information we know that octopus belongs to phylum Mollusca.

So, the correct answer is option B.

Note: They adapt various strategies to protect themselves like expulsion of ink, use of camouflage and threat displays, ability to jet quickly through the water and hide and even deceit. All the octopuses are venomous, but only the blue-ringed octopuses. The largest known octopus species is known as the giant pacific octopus. They are deadly to humans. Octopus have a single, posterior-located gonad.