Biological Classification

Step 1: Evaluate Each Row:

• I. Scyphozoa (Jellyfish): The medusa stage is dominant. The polyp stage is reduced or absent in the life cycle. \Aurelia is a classic example. The description "Only medusoid zooids" is acceptable in the context of general classification contrasts (vs Anthozoa). (Correct)
• II. Anthozoa (Sea Anemones/Corals): They exist only in the Polyp form. They do not have a Medusa stage. \Adamsia is a Sea Anemone. The feature "Polyp and Medusa" is wrong. (Incorrect)
• III. Hydrozoa: They typically exhibit alternation of generations (Metagenesis) with both Polyp and Medusa stages (e.g., \Obelia). Some are only polyps (\Hydra), but the example given is \Obelia, which has both. The feature "Only polypoid" is incorrect for the group/example pair. (Incorrect)
• IV. Hirudinea (Leeches): These annelids have anterior and posterior suckers for attachment and locomotion. \Pontobdella is a marine leech. (Correct)

Step 2: Conclusion:
Combinations I and IV are correct.

- Lasso cells are characteristic of Cnidaria, not Porifera.
- Ctenophora has colloblasts, not choanocytes (which belong to Porifera).
Hence, I and III are incorrect combinations. II and IV are correct.

Concept: This requires matching phylum/class with a unique structural feature and a corresponding example.
Explanation: I. Nematoda ({Ancylostoma}) use renette glands for osmoregulation. II. Crustacea ({Palaemon}) use green glands (or antennal glands) for excretion. III. Cephalopoda ({Sepia}) use an ink gland for defense. IV. Echinoidea ({Echinus}) have the Aristotle's lantern, a complex chewing apparatus. All four combinations are correct.