Polymorphism in Coelenterata

Introduction

The Animal kingdom’s Phylum Coelenterata is a group of aquatic or marine animals. They are generally found adhering to the rocks at the sea bottom. These are the most basic and multicellular invertebrate invertebrates that live independently or in colonies.

Polymorphism is characterised as the “phenomenon of the occurrence of several physiological and morphological forms within a single species indicated by a wide range of variation.”

Table of Contents

• Definition and Classification of Coelenterata
• Phylum Coelenterata Characteristics
• Origin and Forms of Polymorphism
• Polymorphism in Coelenterata
• Importance of Polymorphism
• Frequently Asked Questions – FAQs

Definition and Classification of Coelenterata

Definition of Coelenterata

It is defined as any invertebrate animal belonging to the phylum Coelenterata, such as hydras, jellyfishes, sea anemones, and corals, with a single internal cavity for digesting, excretion, and other activities, as well as the tentacles on the oral end.

Classification of Coelenterata

Coelenterates can be classified into three classes:

• Anthozoa (E.g., Metridium, Xenia)
• Hydrozoa (E.g., Hydra, Obelia)
• Scyphozoa (E.g., Aurelia aurita, Rhizostoma)

Phylum Coelenterata Characteristics

• These creatures are typically found in aquatic or marine environments.
• The tissue-level organisation is present in these organisms.
• Tentacles that are slender and short surround the mouth.
• They are diploblastic animals, which have two layers of cells in their bodies:
• Ectoderm – The cells outside the body are made up of one layer.
• The other is endoderm, which makes up the body’s inner lining.
• Their bodies contain cavities.
• The body is symmetrical in all directions.
• Both intracellular and extracellular digestion are involved.
• The neurological and circulatory systems are both missing.
• Simple diffusion allows them to excrete and breathe.
• Asexual reproduction is accomplished through budding.
• Only a few Coelenterates use the sexual mechanism of reproduction.

Origin and Types of Polymorphism

Origin of Polymorphism

Many theories exist to explain how polymorphism in coelenterates began.

• Polyorgan theory: According to this theory proposed by Huxley (1859), Eschscholtz (1829), E. Metschnikoff (1874), and Muller (1871), individuals of a colony are basically organs of a medusoid individual, having multiplied and moved from their original places to their current evolved positions.
• Polyperson theory: According to this theory, a colony is not a single individual but rather a collection of modified individuals whose structure has altered due to labour division. They’ve all evolved from a primitive zooid called a polyp.
• Medusoid theory: According to the theory, the gastrula siphonophore larva was a medusoid individual from which zooids or individuals emerged by budding from the subumbrella.

Forms of Polymorphism

Some few coelenterates, such as Hydra and sea anemone, are monomorphic, where only polyp phase is found, but other coelenterates display polymorphism.

Dimorphism: Hydrozoan colonies, such as Campanularia and Tubularia, only have two types of zooids: feeding zooids (gastrozooids) and medusae (nectophores) that bud off from the stem (gastrozooids).

Trimorphism: Trimorphic species include Obelia and Plumularia, which feature medusa-producing blastostyle or gonozooids in addition to gastrozooids and medusa.

Polymorphism: In the order Siphonophora, zooids such as Diphyes, Halistemmia, Stephalia, and Physalia are so heavily changed that they resemble organs of a single body rather than colony members.

Polymorphism in Coelenterata

Polymorphism is the existence of multiple types of structurally and functionally diverse individuals within a population.

The phylum Coelenterata’s class Hydrozoa contains a huge number of colonial species with several forms of individuals known as zooids. Polyp and medusa are the two primary zooids found in coelenterates.

1. Polyp:
• Polyps in Hydrozoa have a tubular body with a mouth at one end encircled by tentacles. The other end is normally blind and linked to the substratum through the pedal disc.
• The majority of polyps are sessile.
• They undergo asexual reproduction.
2. Medusa:
• Medusa has a bowl or umbrella-shaped body with peripheral tentacles and a mouth centrally positioned on the lowest concave surface’s projection called manubrium.
• Medusas move about often.
• They undergo sexual reproduction.

Importance of Polymorphism

• It is necessary for the division of labour among the zooids.
• Distinct forms are assigned different functions. Polyps, for example, are focused on feeding, defence, and asexual reproduction, whereas medusa is focused on sexual reproduction.

Related Links:

• Budding
• Protista
• Eukaryotic Cells
• Animal Kingdom- Animalia Phylum, Subphylum