Question

Which is the enemy of Hydra?
A. Mesostoma
B. Macrostomum
C. Microstomum
D. Gunda

Answer 1

Hint: As Hydra is a Cnidarian, few predators are found to attack Cnidarians due to their nematocysts, which make them unpalatable. Tortoise, fish, crabs, echinoderms and platyhelminthes are some of the known predators of marine cnidarians. Only aquatic predators usually feed on Hydra hence can be called as an enemy.

Complete explanation:
Option A Mesostoma: Mesostoma species and other typhloplanid flatworms are predators found in a wide variety of habitats. They eat lots of mosquito larvae, chironomid larvae, and some daphnids, but not many copepods and ostracods.
Option A is not correct.
Option B Macrostomum: Macrostoma species inhabit different aquatic and moist environments. Many of these small worms feed on unicellular algae such as diatoms, others on zooplanktons on or other smaller benthic invertebrates.
So, Option B is not correct.
Option C Microstomum: Microstomum is a genus of flatworms in the family microstomidae. They feed on microscopic crustaceans, bacteria, and organic particles and can be found under rocks, submerged leaves, and other trash. These platyhelminthes feed on cnidarians like Hydra.
Option C is correct.
Option D Gunda: Gunda is a genus of moths of the family Bombycidae. The larvae have been recorded feeding on Ficus elastica.
So, option D is not correct.

Therefore, Option C) is the correct answer.

Note:
Biologists are especially interested in Hydra because of their regenerative ability. They do not appear to die of old age or age at all. Hydra means a many-headed serpent or monster in Greek mythology that was slayed by Hercules and each head of which when cut off was replaced by two others.