Question

The tentacles of Obelia are
A. Hollow
B. Solid
C. Internally chambered
D. Spiny and hollow

Answer 1

Hint: Obelia belongs to marine and freshwater animals that have both the polyp and medusa stages in their life cycle. It comes under the phylum cnidaria and is a genus of hydrozoans. A tentacle is flexible, elongated organs which are found in some animal species and mostly invertebrate. The most common function of tentacles is that they are used mostly in grasping and feeding.

Complete step-by-step answer:
- Hollow: The hollow tentacles are found in the sea-anemone which is present around their mouth and helps them to catch their food. It looks like plants but usually, they belong to the animal kingdom.
- Solid: The mouth of Obelia is surrounded by tentacles around it which is present during the polyp stage. It helps in catching their prey. The tentacles are covered in nematocysts and suctorial pads.
- Internally chambered: The polyps consist of the columnar trunk with a ring of tentacles. The tentacles can be withdrawn inside the body cavity and become enlarged to catch their prey. They contain cnidocytes.
- Spiny and hollow: Sea urchin has hollow and spiny tentacles. They have spiny tentacles for their defence.
Hence, the correct answer is B.

Note: Many of the tentacles are receptive organs and have a vision. Bryozoa is a tiny creature of moss that have tentacles around their mouth and are cylindrical.