Types of Invertebrates

Invertebrates can be categorized into nine types which belong to the following phyla.

• Phylum: Protozoa
• Phylum: Porifera
• Phylum: Cnidaria
• Phylum: Annelida
• Phylum: Platyhelminthes
• Phylum: Aschhelminthes
• Phylum: Arthropoda
• Phylum: Mollusca
• Phylum: Echinodermata

Characteristics of Protozoa

The main characteristics of Protozoa are as follows.

• Unicellular: Single-celled organisms.
• Habitat: Freshwater, marine environments, and soil.
• Shape: Different shapes and sizes..
• Nutrition: Autotrophic, heterotrophic, or both.
• Reproduction: Asexual reproduction by fission, schizogony, or budding. Some reproduce sexually.
• Parasitic: Free-living or parasitic.

Also Read: Vertebrata – Definition, Classification, Characteristics 

Characteristics of Porifera

The main characteristics of Porifera are as follows.

• Body Symmetry: Radially symmetrical or asymmetrical.
• Body structure: Simple body structure with pores and canals lined with choanocytes.
• Germ layers: Diploblastic.
• Organization: Cellular grade of organization.
• Habitat: Marine or freshwater species.
• Reproduction: Hermaphrodite with internal fertilization.

Characteristics of Cnidaria

The main characteristics of Cnidaria are as follows.

• Body symmetry: Radial symmetry.
• Germ layers: Diploblastic
• Gastrovascular cavity: Saclike coelenteron with one mouth-like opening..
• Tentacles: Tentacles with nematocytes present.
• Nematocysts: Nematocysts present on specialized cells called cnidocytes Nematocysts contain toxins to immobilize prey.
• Coelom: They are acoelomate i.e. coelom is absent. But a thick, elastic, jelly-like substance called mesoglea is present in between the outer and inner body layers.
• Nervous system: Nerve net present.

Characteristics of Annelida

The main characteristics of Annelida are as follows.

• Body segments: Small ring-like segmented body covered with a thin cuticle.
• Body Symmetry: Bilaterally symmetrical.
• Digestive system: Digestive system is complete.
• Circulatory system: Circulatory system is closed type.
• Respiration: Respiration through the body surface.
• Excretion: Excretory organs are nephridia.
• Coelom: A protective fluid-filled sac is present around the digestive system.
• Nervous system: Brain and nervous system present.
• Habitat: Damp soil, freshwater, and marine water.

Also Read: Levels of Organization in Animals

Characteristics of Platyhelminthes

The main characteristics of Platyhelminthes are as follows.

• Body structure: Soft, unsegmented bodies are dorsoventrally flattened and leaf-like.
• Body symmetry: Bilateral symmetry.
• Digestive system: Incomplete digestive system.
• Respiration: Simple diffusion through the body surface.
• Excretory system: Flame cells and protonephridia present.
• Germ Layers: Triploblastic.
• Coelom: Coelom is absent.

Characteristics of Aschelminthes

The main characteristics of Aschelminthes are as follows.

• Body symmetry: Bilaterally symmetrical, cylindrical, and unsegmented.
• Coelom: Fluid-filled pseudocoelom present.
• Cuticle: External cuticle present which is molted periodically.
• Systems: Well-developed nervous system and excretory system are present.
• Size: Size varies from microscopic to approximately 1 meter long.
• Appearance: Colorless and tubular in appearance.
• Reproduction: Sexual reproduction.
• Habitat: Aquatic or terrestrial.
• Parasitic: Parasitic or free-living.

Also Read: Difference Between Protostomes And Deuterostomes

Characteristics of Arthropoda

The main characteristics of Arthropoda are as follows.

• Exoskeleton: Exoskeleton is made of chitin.
• Body segments: The body is segmented into three regions: head, thorax, and abdomen.
• Appendages: Jointed appendages.
• Body symmetry: Bilaterally symmetrical body.
• Circulatory system: Circulatory system is open type.
• Sensory organs: Antennae, eyes, statocysts, and auditory organs.
• Respiration: Respiration through the body surface or trachea.
• Excretion: Excretory organs are Malpighian tubules and green glands.
• Reproduction: Sexual reproduction with internal or external fertilization.
• Habitat: Land, water, and soil.

Characteristics of Mollusca

The main characteristics of Mollusca are as follows.

• Body: Soft, unsegmented body is covered by a calcareous shell. The body is divided into three parts – the head, a visceral mass, and a ventral foot.
• Mantle: A mantle with a mantle cavity is used for breathing and excretion. The radula, a ribbon of teeth is present on the mantle.
• Nervous system: Specific nervous system present.
• Respiration: Respiration through gills.
• Body symmetry: Bilaterally symmetrical.
• Germ Layers: Triploblastic.

Also Read: Diploblastic And Triploblastic Organization

Characteristics of Echinodermata

The main characteristics of Echinodermata are as follows.

• Body symmetry: Pentaradial symmetry.
• Spiny skin: Skin is piny and bumpy.
• Water vascular system: A specialized water vascular system is used for feeding and breathing.
• Endoskeleton: Endoskeleton is made up of calcareous ossicles.
• Tube feet: Tube feet with suckers present.
• Regeneration: Echinoderms can regenerate themselves.

The invertebrates are characterized by the absence of a vertebral column and they can be classified mainly into nine types according to the Phyla. Invertebrates are the largest group in the animal kingdom which are mainly included in the Phyla Protozoa, Porifera, Cnidaria, Annelida, Platyhelminthes, Aschhelminthes, Arthropoda, Mollusca, and Echinodermata.

Invertebrate animals play an important role as agricultural pests, parasites, or vectors of parasitic infections to humans and other vertebrates and also help in plant pollination. In this article, we will learn about different types of invertebrates along with their characteristics.