Taenia tapeworm and Fasciola liver fluke are examples of animals belonging to which invertebrate phylum in the animal kingdom?

Introduction / Context:
Parasitic worms that infect humans and domestic animals are classified into different phyla based on body structure, body cavity, and other anatomical features. Taenia commonly known as tapeworm and Fasciola known as liver fluke are two important parasites studied in basic zoology. This question asks you to identify the correct phylum to which these worms belong.

Given Data / Assumptions:

• Taenia is a flat, ribbon like tapeworm living in the intestine of its host.
• Fasciola is a leaf shaped liver fluke that lives in the bile ducts of its host.
• Options include Coelenterata, Platyhelminthes, Annelida, Arthropoda, and Nematoda.
• We focus on broad body plan characteristics such as shape and presence of body cavity.

Concept / Approach:
Platyhelminthes is the phylum of flatworms. Members are dorsoventrally flattened, triploblastic, and acoelomate without a true body cavity. They often have incomplete digestive systems and show varying degrees of parasitism. Taenia and Fasciola are classic examples of parasitic flatworms belonging to Platyhelminthes. Coelenterata includes radially symmetrical animals like jellyfish. Annelida includes segmented worms such as earthworms. Arthropoda includes joint legged animals like insects, and Nematoda includes roundworms that are cylindrical and not flattened.

Step-by-Step Solution:
Step 1: Recall the general body shape of Taenia tapeworm, which is long, flat, and segmented into proglottids. Step 2: Recall that Fasciola is also flat and leaf shaped with a complex life cycle involving snails and vertebrate hosts. Step 3: Recognise that flat, acoelomate body organisation with high parasitic adaptation is typical of Platyhelminthes. Step 4: Coelenterata cnidaria contains animals like hydra and jellyfish, which have radial symmetry and do not resemble these worms. Step 5: Annelida comprises cylindrical segmented worms with a true coelom and setae, not flat parasites like Taenia and Fasciola. Step 6: Arthropoda includes exoskeleton bearing, joint legged animals such as insects and crustaceans, which are very different from worms. Step 7: Nematoda includes roundworms like Ascaris that are cylindrical, not flattened, so this option also does not fit.

Verification / Alternative check:
Zoology textbooks commonly introduce Platyhelminthes by listing planarians, liver flukes, and tapeworms as key representatives. Fasciola hepatica the sheep liver fluke and Taenia solium or Taenia saginata tapeworms are described in detail under this phylum, including their morphology and life cycles. In contrast, classification chapters place jellyfish and hydra under Coelenterata, earthworms under Annelida, crabs and insects under Arthropoda, and Ascaris under Nematoda. This clear grouping supports the placement of Taenia and Fasciola in Platyhelminthes.

Why Other Options Are Wrong:
Coelenterata animals are radially symmetrical and aquatic with tentacles, not flat intestinal or liver parasites. Annelids have segmented cylindrical bodies, chaetae, and a coelom, features absent in Taenia and Fasciola. Arthropods have exoskeletons, jointed appendages, and segmented bodies, again very different from flatworms. Nematodes are round in cross section and lack the dorsoventral flattening that characterises flatworms.

Common Pitfalls:
Students sometimes confuse Platyhelminthes and Nematoda because both include parasitic worms. The key difference is body shape: flatworms versus roundworms. Remember that the prefix platy means flat and helminthes means worms, which directly describes the appearance of Taenia and Fasciola. Associating typical examples with each phylum helps to avoid classification errors.

Final Answer:
Taenia tapeworm and Fasciola liver fluke are examples of phylum Platyhelminthes.