Question

Sessile, cylindrical form of coelenterate reproduced by asexual reproduction is (a) Polyp (b) Medusa (c) Both (a) and (b) (d) None of these

Short answer

The correct answer is (a) Polyp.

Step-by-step solution

Understand the terminology

Know what coelenterates are - They are a group of invertebrates which include polyps and medusae. Understand that sessile means the organism does not move (it is attached to a substrate), and cylindrical form refers to the shape of the organism. Also know that asexual reproduction is a type of reproduction where one parent produces offspring without fertilization.

Identify the form of coelenterates

Coelenterates exist in two forms: Polyp and Medusa. A polyp is the sessile, cylindrical form that reproduces asexually. This form is attached to a substrate. In contrast, a medusa is the mobile, umbrella-shaped form.

Make a conclusion

Given that the question describes a sessile, cylindrical form of coelenterate reproduced by asexual reproduction, the correct answer is Polyp.

Key concepts

Polyp

When studying the fascinating world of coelenterates, we come across diverse life forms, one of which is the polyp. Imagine a small, cylinder-shaped creature, steadfastly attached to a rock or another solid surface in the water. This is what we describe as a polyp. It is distinct not only for its shape but also for its sedentary lifestyle, unlike some of its more mobile cousins in the coelenterate family.

Polyps exhibit radial symmetry, which means that their body plan is structured like a pie that can be cut into several identical slices. This symmetry is ideal for their stationary existence. As a result, polyps are well-adapted to catch food particles floating by in the water, using their tentacles which radiate out from their mouth. This mouth, incidentally, also serves as the exit point for waste material.

A common example of a polyp is the sea anemone or the younger stages of a jellyfish. Despite their simplicity, polyps have a complex role in aquatic ecosystems, often offering shelter to other marine life and contributing to biodiversity.

Asexual Reproduction in Coelenterates

Asexual reproduction among the coelenterates, such as polyps, is akin to a magic act where one performer splits into two. Fascinatingly, polyps reproduce asexually through a process known as budding. In this process, a new organism develops from an outgrowth or bud due to cell division at one particular site.

These buds grow into full-sized polyps and eventually break away from the parent organism, although sometimes they stay connected, forming colonies that can cover large areas. This mode of reproduction is advantageous in stable environments where the chances of survival are high, as it allows for rapid population growth without the complexities of mating. Asexual reproduction is not limited to budding; other forms include fission, where an organism splits into two or more parts, and regeneration, where a new organism grows from a fragment of the parent.

The simplicity and efficiency of asexual reproduction in coelenterates ensure their continued success in a variety of marine habitats, leading to the widespread presence of these intriguing creatures across the oceans of the world.

Medusa

Contrasting the stationary polyp, the medusa stage of coelenterates is built for travel. Picture a jellyfish: free-swimming, with its umbrella-shaped body and trailing tentacles, undulating gracefully through the water current. This is the medusa form, named after the enchanting yet fearsome creature from Greek mythology whose hair comprised venomous serpents.

The medusae are the grown-up, often sexually mature stage in the life cycle of many coelenterates. This stage is adapted for a pelagic life, drifting, and swimming in the open sea. Interestingly, medusae reproduce sexually, releasing sperm and eggs into the water, leading to the formation of free-swimming larvae that eventually settle down and transform into the polyp stage.

An incredible aspect of this life stage is the way medusae can use their tentacles, not just for locomotion but also to capture prey. The tentacles are armed with specialized cells known as cnidocytes, which contain stingers capable of delivering paralyzing toxins. This versatile life stage plays a pivotal role in marine ecosystems, often influencing the population dynamics of other marine animals.