Ascaris lumbricoides is a parasitic

Step 1: Analyze the question The question asks which group of organisms Ascaris lumbricoides belongs to.

Step 2: Explain the concept Worm-like parasites are classified into phyla based on body shape:

• Platyhelminthes (flatworms): flat, ribbon-like or leaf-like bodies, e.g. Taenia solium (tapeworm) and Schistosoma (blood fluke).
• Nematoda (roundworms): cylindrical, unsegmented bodies tapering at both ends, with a complete digestive tract (mouth and anus), e.g. Ascaris lumbricoides and Ancylostoma (hookworm).
• Annelida (segmented worms): bodies divided into rings, e.g. earthworm and leech.
• Arthropoda: jointed legs and an exoskeleton, e.g. insects and spiders.

Step 3: Apply it Ascaris lumbricoides is the human intestinal roundworm. It has:

• a long, cylindrical, unsegmented body
• a complete alimentary canal
• separate sexes (the female is larger than the male)

It lives in the human small intestine and causes ascariasis. It spreads through food or water contaminated with its eggs, usually due to poor sanitation.

Step 4: Eliminate the wrong options

• A. Flat worm: wrong, since flatworms are Platyhelminthes such as tapeworms and flukes.
• C. Arthropod: wrong, because Ascaris has no jointed appendages.
• D. Elastic worm: not a biological classification.

Answer: B. round worm

Tip: Remember the name "Ascaris" with "round": Ascaris = Nematoda = roundworm. Also, tapeworm is flat, and Ascaris and hookworm are round. Questions on this topic appear often in WASSCE and NECO.