Essential Characteristics and Groups of Higher Invertebrates Explained
The organisms present in Animalia can be differentiated into phylums including Porifera, Cnidaria, Ctenophora, Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca, Echinodermata, Hemichordata, and Chordata.
Here, let us know in detail about the higher invertebrate animal phyla.
Characteristics of Higher Invertebrate Animals
Phylum Annelida
Earthworms and leeches belong to this category. The characteristics of phylum Annelida are:
Example of Phylum Annelida is Leech
They could be water animals or terrestrial, free-living or parasitic.
These are coelomate as they need a real coelom. This means that the coelom or the body cavity is enclosed by the mesoderm on all sides.
They are triploblastic and have bilateral symmetry.
They have a closed circulatory system, which means that blood is circulated through blood vessels and never leaves them.
They show metamerism, which suggests that in their body similar segments are repeated.
They have organs called nephridia for excretion.
Aquatic annelids have appendages called parapodia for locomotion. All annelids have setae, stiff bristle-like structures for attachment.
Their nervous system consists of paired ganglia (collections of nerve cell bodies) and a double ventral nerve cord connected by lateral nerves.
They undergo sexual reproduction. Some of them are unisexual while others are bisexual.
Phylum Arthropoda
Among all the phyla of this Animal kingdom, this is the largest animal phyla. These include insects, prawns, crabs, spiders, scorpions, millipedes, and centipedes.
Example of Phylum Arthropoda is Scorpion
Let us look at the characteristics of Arthropoda:
These are triploblastic, coelomate, bilaterally symmetrical
These have appendages with joints for locomotion (arthros = joint, pods = feet).
They are segmented like Annelids.
Their body is protected by a tough covering called an exoskeleton, made of chitin.
Their body is divided into three parts viz. head, followed by the thorax, and finally the abdomen.
Different arthropods respire using different organs such as tracheae, book lungs, book gills.
They have an open circulatory system, viz. the blood flows out of the blood vessels into the body cavity and the tissues are bathed in blood.
Compound eyes and statocysts are the sense organs that are present
Excretion is completed by various organs like malpighian tubules and green lands.
They are dioecious and development is often indirect, which means that they have a larval stage.
Phylum Mollusca
This phylum of this Animalia includes animals like snails, clams, oysters, octopus, and squid.
Example of a Phylum Mollusca is Octopus.
The characteristics of phylum Mollusca are:
Their body is split into the top , foot (a large organ used for locomotion) and visceral mass(all the organs are contained in this).
Their head has an antennae with eyes.
The mantle, that is a soft covering, covers the visceral mass.
In most molluscs, the mantle cavity is covered by a calcareous shell.
Their mouth features a rasping organ called a radula.
They have an open circulatory system.
They are dioecious and development is indirect.
Phylum Echinodermata
These include marine invertebrates such as starfish.
Example of a Phylum Echinodermata is Starfish.
The following are the characteristics of phylum Echinodermata:
They are radially symmetrical, but their larvae are bilaterally symmetrical.
They have a calcareous endoskeleton.
They have a water vascular system, constituting a network of channels. It has two functions: the first one is the circulation of seawater through the body (for the exchange of food, waste substances and gases), and the second one is locomotion by tube feet which are a part of this system.
They are dioecious and development is indirect.
Phylum Chordata
Example of Phylum Chordata is Hemichordata.
The following are the characteristics of phylum Chordata:
They are a worm-like marine.
The body can be divided into an anterior proboscis, followed by a collar and then a trunk.
They have an open circulatory system and respire through gills.
They are dioecious and development is indirect.
FAQs on Higher Invertebrates in Kingdom Animalia: A Complete Guide
1. What are higher invertebrates?
Higher invertebrates are animals that lack a backbone but possess a true coelom, which is a body cavity completely lined by the mesoderm. This advanced feature allows for greater complexity in organ development and arrangement compared to lower invertebrates. They exhibit an organ-system level of body organisation.
2. Which phyla are considered higher invertebrates? Provide examples.
The major phyla classified as higher invertebrates include:
- Phylum Annelida: Examples include the earthworm and leech.
- Phylum Arthropoda: Examples include insects (cockroach), crustaceans (prawn), and arachnids (spider).
- Phylum Mollusca: Examples include the snail, octopus, and oyster.
- Phylum Echinodermata: Examples include the starfish and sea urchin.
- Phylum Hemichordata: An example is Balanoglossus (acorn worm).
3. How do higher invertebrates fundamentally differ from lower invertebrates?
The fundamental difference lies in the nature of their body cavity or coelom. Higher invertebrates are eucoelomates, meaning they have a true coelom derived from the mesoderm. In contrast, lower invertebrates are either acoelomates (lacking a body cavity, like Platyhelminthes) or pseudocoelomates (having a false coelom not completely lined by mesoderm, like Aschelminthes). This presence of a true coelom in higher invertebrates supports more complex organ systems and greater body size.
4. What are the defining characteristics of Phylum Annelida?
Phylum Annelida is defined by several key characteristics, including:
- Metameric Segmentation: Their body is distinctly divided into similar segments, both externally and internally.
- True Coelom: They are the first phylum to exhibit a true coelom, which allows for better organ packaging.
- Closed Circulatory System: Blood circulates exclusively through a network of vessels.
- Nephridia: They possess specialised organs called nephridia for osmoregulation and excretion.
- Locomotion: They move using setae or parapodia (in aquatic forms).
5. Why is Phylum Arthropoda considered the most successful phylum in the animal kingdom?
Arthropoda's success is attributed to several evolutionary innovations. Their chitinous exoskeleton provides excellent protection and prevents water loss. The presence of jointed appendages allows for highly adapted and efficient movement, feeding, and sensory functions. Furthermore, their ability to inhabit nearly every habitat on Earth and the sheer number of species (over two-thirds of all named species) underscore their evolutionary success.
6. What are the key features of Phylum Mollusca?
Molluscs are characterised by a soft, unsegmented body which is typically divided into three main parts: a head, a visceral mass, and a muscular foot. Key features include:
- A soft layer of skin called the mantle, which covers the visceral mass and often secretes a hard calcareous shell.
- The presence of a file-like rasping organ in the mouth called a radula, used for feeding.
- An open circulatory system in most cases, where blood flows through a body cavity called the hemocoel.
7. Explain the significance of the water vascular system in Echinoderms.
The water vascular system is a unique and defining feature of Phylum Echinodermata. It is a hydraulic system of canals connected to tube feet. Its significance is immense as it performs multiple vital functions, including locomotion (movement), respiration (gaseous exchange), food capture, and the transport of nutrients and waste products. This system is a key reason for the unique biology of animals like starfish.
8. What characteristics place Hemichordates as a link between invertebrates and chordates?
Hemichordates are considered an evolutionary link because they exhibit features of both groups. They share two key characteristics with chordates: the presence of pharyngeal gill slits and a rudimentary, notochord-like structure called a stomochord in their collar region. However, they retain a typical invertebrate body plan, making them a crucial group for understanding the origins of chordates.
9. What is the primary difference between an open and a closed circulatory system in higher invertebrates?
The primary difference is how blood is circulated. In a closed circulatory system, as seen in Annelids, blood is always contained within vessels and is pumped by a heart, allowing for more efficient transport and higher blood pressure. In an open circulatory system, found in Arthropods and most Molluscs, blood is pumped by a heart into a body cavity called a hemocoel, where it directly bathes the tissues before returning to the heart. This system is generally less efficient.
10. What is metamerism, and which higher invertebrate phylum is a prime example of it?
Metamerism, or metameric segmentation, is a type of body plan where the body is divided into a series of repeating, similar segments. Each segment, or metamere, contains a serial repetition of certain organs and structures. This allows for greater mobility and complexity. The prime example of true metamerism among higher invertebrates is Phylum Annelida, as seen clearly in the body of an earthworm.
