Question

Sea pen is
A. Gorgonia
B. Adamsia
C. Pennatula
D. Physalia

Answer 1

Hint: Sea pens occur in deep and shallow waters from polar seas to tropics. The name sea pen was given to them, due to their resemblance to quill pens.

Complete answer:
Sea pens are marine cnidarians belonging to order Pennatulacea. They are named after the feather-like appearance. The central stalk of the animal has a lower part called the peduncle that anchors the colony in sand or mud, and an upper part called the rachis that bears polyps or branches bearing many numbers of polyps. The central stalk is known as axial or primary polyp. Secondary polyps are those branching from it. Colonies of some genera like Chunella bear few polyps and others bear as many as 35,000. The tentacles and mouth of the primary polyp are degenerate, with little more than a fleshy stem strengthened by the central horny rod.
Many pennatulacea, however, do not resemble pens. For example, the Renilla, sea pansy are found along the Atlantic and Pacific coasts of North America, is a flattened kidney-shaped plate with two fused halves. All the polyps are present on the upper side. Most sea pens are orange, yellow, red, or brown in color.

Hence, the correct answer is option (C).

Note: Sea pens can expand or deflate by taking or expelling in water through interconnecting hollow canals of the polyps. They feed on organisms captured by the tentacles present at the end of each polyp. Most sea pens glow or luminesce, when they are stimulated or otherwise touched.