In which of the following animal phyla, is the body divided into head, thorax and abdomen?

The correct answer is Arthropoda.
Key Points Arthropoda

• Phylum Arthropoda is the largest phylum in the animal kingdom.
• Over two-thirds of all named species on Earth are arthropods.
• Phylum Arthropoda was first created by Von Seibold in 1845.
• The body of arthropods is covered by a chitinous exoskeleton.
• The body of arthropods consists of a head, thorax, and abdomen.
• Phylum Arthropoda has jointed appendages.
• The respiratory organs of arthropods are gills, book gills, book lungs or tracheal system.
• The circulatory system in Arthropoda is of open type.
• Excretion in Arthropoda takes place through malpighian tubules.

Additional Information Annelida:

• Annelida are aquatic or terrestrial, free-living, and sometimes parasitic.
• They are coelomate. This allows true organs to be packaged in the body structure.
• They are bilaterally symmetric and triploblastic.
• Examples: Nereis - Hirudinaria.​

Chordata:

• Animals belonging to phylum Chordata are fundamentally characterized by the presence of a notochord, a dorsal hollow nerve cord, and paired pharyngeal gill slits.
• They are bilaterally symmetrical, triploblastic, coelomate with the organ-system level of organization.
• Phylum Chordata is divided into three subphyla: Urochordata or Tunicata, Cephalochordata, and Vertebrata.
• Examples: Urochordata – Ascidia, Salpa, Doliolum; Cephalochordata – Amphioxus or Lancelet.

​Mollusca:

• Example: Pila, Octopus
• Excretion takes place through the kidneys.
• Blood is colorless.
• Respiration takes place through gills or ctenidia.
• The alimentary canal is well developed.
• The mantle is always present in it.
• The body is divided into a head and a muscular foot.