COLENTERATES

 

Coelenterates (Phylum Cnidaria - also known as Cnidarians)

General Characteristics

  • Coelenterates are aquatic animals, mostly found in marine environments.

  • Their bodies are diploblastic (made of two layers: ectoderm and endoderm).

  • They show radial symmetry—you can divide their body into equal parts through a central axis.

  • They have a gastrovascular cavity (coelenteron) that functions as both mouth and gut.

  • They lack specialized respiratory, circulatory, and excretory systems.

  • They have special stinging cells called cnidocytes on their tentacles for defense and capturing food.

  • Two basic body forms:

    • Polyp (e.g., Hydra) – cylindrical and attached.

    • Medusa (e.g., Jellyfish) – umbrella-shaped and free-swimming.

Classification of Coelenterates

Cnidaria is divided into three major classes:

  1. Hydrozoa

    • Can be solitary (Hydra) or colonial (Obelia).

    • Show both polyp and medusa forms.

    • Example: Hydra, Obelia, Physalia (Portuguese man o’ war).

  2. Scyphozoa

    • Medusa form is dominant.

    • Mostly jellyfish.

    • Example: Aurelia (true jellyfish).

  3. Anthozoa

    • Only polyp form, no medusa.

    • Includes corals and sea anemones.

    • Example: Sea fan (Gorgonia), Sea anemone (Metridium), Coral (Madrepora).


Other Systems in Coelenterates

  • Nervous system: Simple nerve net with no brain or central nervous system.

  • Digestive system: Incomplete; only one opening (mouth) for both food intake and waste removal.

  • Reproduction: Can reproduce asexually (budding in polyps) and sexually (in medusae or polyps).

Polymorphism in Coelenterates

Polymorphism means the presence of different types of individuals (zooids) within the same species or colony.

  • Polyp: Asexual, cylindrical, attached to surfaces.

  • Medusa: Sexual, umbrella-shaped, free-swimming.

  • Example: In Obelia, there are different zooids like feeding zooids (gastrozooids) and reproductive zooids (gonozooids).

Polymorphism helps in division of labor and survival.

Mesenteries in Coelenterates

Mesenteries are internal walls or partitions found in the gastrovascular cavity of Anthozoans (like sea anemones and corals).

  • They increase the surface area for digestion and absorption.

  • Also contain gonads and muscle fibers for better control over movement.

Corals and Coral Reefs

Corals are marine polyps that secrete calcium carbonate to form hard exoskeletons. These build up over time to form coral reefs.

Types of Coral Reefs

  1. Fringing Reef – directly attached to the shoreline.

  2. Barrier Reef – separated from the shore by a lagoon.

  3. Atoll – ring-shaped reef surrounding a central lagoon, often on submerged volcanoes.

Importance of Coral Reefs

  • Biodiversity hotspots – Home to thousands of marine species.

  • Protect coastlines from erosion and storm surges.

  • Provide resources like fisheries and tourism.

  • Serve as natural indicators of ocean health.

  • Help in carbon cycling and nitrogen fixation.

In Simple Terms:

Think of coelenterates as soft-bodied animals with tentacles that sting. They can float like jellyfish or stay attached like corals. Some live alone, some in colonies. Corals build reefs that act like underwater cities for fish and protect our shores.

Comments

Post a Comment

Popular posts from this blog

Protists and Metazoans

Image
Protists Protists are a diverse group of mostly single-celled organisms that belong to the kingdom Protista. They are eukaryotes, meaning their cells contain a nucleus and other specialized organelles. Protists can be found in a variety of environments, particularly in water or moist surroundings. They can resemble animals, plants, or fungi in their structure and behavior. Some move using cilia, flagella, or by changing shape (amoeboid movement), while others are immobile. Protists include organisms like amoebas, algae, and paramecia. Their modes of nutrition vary as well—some perform photosynthesis (like algae), others consume food particles (like protozoa), and some can do both depending on conditions.   Metazoans Metazoans, also known as animals, are multicellular organisms that belong to the kingdom Animalia. Unlike protists, metazoans are composed of many cells that are organized into tissues, organs, and systems. These organisms are heterotrophic, meaning they rely on con...
Read more

PROTOZOA - Characteristics, Classification, feeding mechanism, Disease

Image
  Here's a comprehensive, easy-to-understand guide on protozoa , covering their characteristics, classification, feeding methods, diseases, and more—complete with illustrative images. ​ 🧬 What Are Protozoa? Protozoa are microscopic, single-celled organisms found in various environments, including freshwater, marine habitats, and soil. Some protozoa are free-living, while others are parasitic, causing diseases in humans and animals. ​ 🔍 Key Characteristics Cell Type : Eukaryotic (possess a true nucleus and membrane-bound organelles). Structure : Unicellular, lacking cell walls. Nutrition : Heterotrophic (consume organic matter); some are mixotrophic (both autotrophic and heterotrophic). Locomotion : Move using cilia, flagella, or pseudopodia. Reproduction : Primarily asexual (binary fission); some exhibit sexual reproduction. ​ 🧭 Classification of Protozoa Protozoa are classified based on their mode of locomotion: ​ Amoeboids (Sarcodina) : Move using...
Read more

PORIFERA

Image
  Porifera (Sponges)  Porifera, commonly known as sponges, are the simplest multicellular animals. These aquatic invertebrates play a significant role in aquatic ecosystems by filtering water and providing habitat for various organisms. 🧬 Classification of Porifera Porifera are classified into three major classes based on the type of skeleton and body structure: Class Calcarea – Calcareous sponges with calcium carbonate spicules. Class Hexactinellida – Glass sponges with six-rayed siliceous spicules. Class Demospongiae – The largest class, containing sponges with spongin fibers or silica-based spicules. 🌀 Canal System in Porifera The canal system is the defining feature for water circulation and feeding: Ascon Type – Simplest structure with a central cavity (spongocoel). Sycon Type – Wall folded into canals for increased surface area. Leucon Type – Highly complex with chambers and canals, found in most sponges. 🍽️ Feeding Mechanism Spon...
Read more