Animal Animalia Lower Invertebrates

May 09, 2023, 16:45 IST

Are you fascinated by the weird and wonderful creatures that inhabit our world? Do you marvel at the diversity of life, from tiny organisms to massive creatures that roam the land and sea? If so, join us on a journey into the fascinating world of Animalia lower invertebrates. From bizarre jellyfish to spineless worms and everything in between, these incredible creatures will awaken you with their unique adaptations and survival strategies. So buckle up, grab your magnifying glass, and explore this amazing kingdom together!

Lower Invertebrates

Invertebrates lack a backbone. "invertebrate" comes from the Latin word vertebra, which means "a joint in the back." Invertebrates include terrestrial and aquatic animals, coming in all shapes and sizes.

There are several thousand known species of invertebrates, making up most of the animal kingdom. Invertebrates can be found on every continent and in almost every environment, from the coldest polar regions to the hottest deserts.

Invertebrates are an extremely diverse group of animals, and they play important roles in nearly every ecosystem. Many invertebrates are essential for decomposing dead plants and animals, which recycle nutrients into the soil. Other invertebrates help control populations of pests and disease-carrying organisms. And still, others are important food sources for other animals.

The lower invertebrates include all invertebrate animals except the protostomes (which include insects, crustaceans, myriapods, molluscs, annelids and arthropods). These animals share a common ancestry with the higher vertebrates (mammals, reptiles, birds and fishes) but diverged from this lineage early in evolutionary history.

The Characteristics of Lower Invertebrates

Many characteristics of lower invertebrates make them unique and interesting creatures. They include:

• Lower invertebrates have a segmented body. It allows them to move in a very specific and coordinated way.
• They have a hard exoskeleton. It helps protect their delicate internal organs from predators and the environment.
• They breathe through spiracles, which are small holes in their exoskeleton.
• Many lower invertebrates can reproduce asexually, so they do not need a mate to produce offspring.
• They are often very sensitive to environmental changes like temperature and humidity.

Classification of Lower Invertebrates

There are many different types of lower invertebrates, each with unique characteristics. Some of the most common lower invertebrates include here:

Phylum Porifera

Phylum Porifera, commonly known as sponges, are a basal clade of animals. They are multicellular organisms that lack true tissues and organs. Sponges are filter feeders that pump water through their bodies to extract nutrients. Most sponges live in marine environments, but a few species live in freshwater.

Sponges were once considered plants because they do not move but they are now known as animals. The earliest sponge fossils date back to the Precambrian period (approximately 600 million years ago). Sponges are thought to have originated in the oceans and then colonised freshwater habitats.

Sponges come in various shapes and sizes, from small vase-shaped sponges to giant barrel sponges that can grow up to 2 meters (6 feet) in length. Most sponge species are hermaphrodites, meaning they have both male and female reproductive organs. However, some species can reproduce asexually by fragmentation.

Sponges play an important role in the marine ecosystem by recycling nutrients and providing habitat for other animals. Some sponges form symbiotic relationships with other organisms, such as algae, bacteria, and certain fishes.

Characteristics of Porifera

• Porifera is a phylum of aquatic animals that contains sponges. "Porifera" comes from the Latin word for "pore". Porifera is multicellular, but its cells are not organised into tissues.
• They do not have a nervous system and lack true organs.
• Although they lack many of the features we typically associate with animals, they are still classified as animals because it is heterotrophic, and they possess the ability to move independently at some point in their life cycle.
• Porifera is primarily marine animals, although a few species live in freshwater. They range in size from microscopic to over 2 meters in length. Most sponge species are sessile (attached to a substrate), but some species can swim or crawl slowly using specialised cells called choanocytes.
• Sponges are filter feeders; they pump water through their bodies to capture small food particles. Most sponges eat their nutrition from bacteria, but some larger sponges eat small crustaceans and other zooplankton.
• Porifera reproduce both sexually and asexually. Many species can regenerate lost body parts, and some species can even produce clones of themselves.

Phylum Platyhelminthes

Platyhelminthes are a species of flatworm-like animals. Many of them are parasites living on or in other animals. The name "Platyhelminthes" comes from the Greek word for "flatworm".

There are three main groups of Platyhelminthes: the cestodes (tapeworms), the trematodes (flukes), and the monogeneans (gill worms). Most Platyhelminthes have flattened bodies, but some are cylindrical. They range in size from a few millimetres to over a meter long.

Platyhelminthes have simple nervous systems, and most do not have eyes. Their mouths are on the underside of their body, and they have a muscular pharynx that helps them suck in food. They also have a gastrointestinal tract but no respiratory or circulatory systems.

The majority of Platyhelminthes are hermaphrodites, meaning that they have both male and female reproductive organs. However, some are monoecious (having only one sex) or dioecious (having two sexes). Fertilisation is usually internal; offspring are released into the environment to fend for themselves.

Characteristics of Phylum Platyhelminthes

• Platyhelminthes are a species of flatworm-like animals. They are bilaterally symmetrical, meaning they have mirror-image left and right sides.
• Their bodies are divided into three main regions: the head, the trunk, and the tail.
• They have a distinct authority with eyespots and a mouth.
• Their gut is simple, with one opening as both the mouth and the anus.
• They lack a circulatory system and rely on diffusion to transport nutrients and oxygen throughout their bodies.
• Many platyhelminthes are parasitic, living off the blood or tissues of other animals.

Phylum Cnidaria / Coelenterata

Phylum Cnidaria / Coelenterata is a group of invertebrate animals that includes hydroids, jellyfish, anemones, and corals. Most members of this phylum are marine animals, but there are also some freshwater and terrestrial species. Cnidarians are characterised by the presence of cnidocytes, which are cells that contain stinging nematocysts. These cells are used for self-defence and for capturing prey.

Cnidarians come in a wide variety of shapes and sizes. The simplest cnidarians are the small hydroids stalk-like creatures that attach themselves to rocks or other hard surfaces in shallow water. Jellyfish are another type of cnidarian; they are free-floating creatures with a gelatinous body with four simple radial symmetries. Anemones and corals are more complex cnidarians; they have cylindrical bodies with specialised tentacles surrounding their mouths.

Cnidarians exhibit two main life cycles: the medusa stage and the polyp stage. The medusa stage is the free-floating, sexually reproductive stage, while the polyp stage is the passive, asexual phase. Most cnidarians alternate between these two phases, but some species spend their entire lives in either the medusa or polyp stage.

Cnidarians play an important role in marine ecosystems as both predators and prey.

Characteristics of Phylum Cnidaria / Coelenterata

• Phylum Cnidaria / Coelenterata is a large species that includes hydroids, jellyfish, anemones, and corals.
• The members of this phylum are characterised by having a saclike body with a central cavity that opens to the exterior through a mouth surrounded by tentacles.
• The body wall comprises two layers of cells, the outer layer called the epidermis and the inner layer called the gastrodermis.
• Between these two layers is a thin non-cellular material called the mesoglea.
• Most cnidarians are sessile polyps that attach themselves to substrates with tentacles facing up into the water to catch prey.
• Some cnidarians are free-swimming medusae.

Phylum Ctenophora

The Phylum Ctenophora is a group of marine invertebrates that includes comb jellies. These animals are characterised by their cilia, which they use to swim and capture prey. Comb jellies are some of the most beautiful creatures in the ocean, with their iridescent bodies and long, flowing cilia. Although they may look delicate, comb jellies are quite tough and can sting predators with their cilia.

Characteristics of Phylum Ctenophora

Phylum Ctenophora is a diverse group of marine invertebrates characterised by their ciliated body and eight comb rows. These animals are often called "comb jellies" or "sea walnuts" due to their appearance. Ctenophores are found in all oceans, from the surface to the deep sea. They range from a few millimetres to over a meter in length.

Ctenophores are unique among animals in several ways:

1. They are the only animal group that uses cilia for locomotion.
2. They are the only animal group with the true tissue-level organisation (i.e., they have more than one cell type).
3. They are the only animal group with secondary larvae (i.e., their larvae look nothing like the adults).
4. They exhibit various colours and patterns thanks to their reflective cells (called iridocytes).

Despite their beauty and uniqueness, ctenophores are often overlooked because they are relatively small and poorly studied. However, recent research has revealed that these creatures play an important role in ocean ecosystems. For example, ctenophores are major predators of zooplankton, which helps to keep populations of these tiny animals in check.

Phylum Aschelminthes

The phylum Aschelminthes is a group of invertebrate animals that includes roundworms, segmented worms, and whipworms. This species is characterised by having a cylindrical body with no head or tail. The Aschelminthes are cosmopolitan, meaning they can be found all over the world in a variety of habitats. Many species of Aschelminthes are parasitic, living off the blood or tissues of their host. Some common diseases caused by Aschelminthes include trichinosis (from eating undercooked pork), ascariasis (from ingesting contaminated food or water), and hookworm disease (from exposure to contaminated soil).

Characteristics of Phylum Aschelminthes

• Phylum Aschelminthes is a large, diverse phylum of parasitic worms. They are often divided into three main groups: the acanthocephalans, the nemerteans, and the rotifers.
• Acanthocephalans are spiny-headed worms that live in the intestines of animals. They have long, thin bodies and no hard exoskeleton. Most acanthocephalans are less than 10 centimetres (4 inches) long.
• Nemerteans are also known as ribbon worms. They have long, slender bodies and a tough outer covering. Some nemerteans can grow over 30 meters (100 feet) long!
• Rotifers are small, microscopic creatures that live in water. They have a wheel-like structure on their head to move around and capture prey.

Frequently Asked Questions (FAQs)

Q1. What are the characteristics of Animalia Lower Invertebrates?

Ans. Animalia Lower Invertebrates include animals that do not have a backbone or spinal column, such as squid, octopus, jellyfish, and worms. These animals are typically characterised by their lack of internal or external skeleton, soft body, and radial or cylindrical symmetry.

Q2. What is the classification of Animalia Lower Invertebrates?

Ans. Animalia Lower Invertebrates are classified as a subphylum of the larger phylum Animalia, which includes all animals with a backbone or spinal column.

Q3. How do Animalia Lower Invertebrates reproduce?

Ans. Animalia Lower Invertebrates typically reproduce through asexual reproduction, where a single individual can produce offspring without needing a mate.

Q4. What are the benefits of Animalia Lower Invertebrates?

Ans. Animalia Lower Invertebrates benefit humans and the global ecosystem. These animals can act as food sources, provide clean water, and provide other essential services such as soil conditioning and nutrient cycling.

Q5. What are the threats to Animalia Lower Invertebrates?

Ans. Animalia Lower Invertebrates are threatened by various factors, including habitat destruction, water pollution, and climate change. These threats can have serious environmental consequences.