Difference Between Annelida and Arthropoda

Main Difference – Annelida vs Arthropoda 

Annelida and Arthropoda are two phyla of the kingdom Animalia. Both Annelida and Arthropoda are composed of segmented animals. The main difference between Annelid and Arthropoda is that Annelida consists of a hydrostatic skeleton whereas Arthropoda consists of an exoskeleton made up of chitin. Animals in both phyla are subdivided into different classes based on their diversity.  The three classes of the phylum Annelida are Polychaeta (marine bristle worms), Oligochaeta (aquatic and terrestrial earthworms) and Hirudinea (leeches). The five classes of the phylum Arthropoda are Crustacea (shrimp, crayfish, and lobster), Arachnida (spiders, ticks, mites and scorpions), Chilopoda (centipedes), Diplopoda (millipedes) and Insecta (bees, butterflies, roaches and beetles).

Key Areas Covered

1. What is Annelida
      – Definition, Characteristics, Classes
2. What is Arthropoda
      – Definition, Characteristics, Classes
3. What are the Similarities Between Annelida and Arthropoda
      – Outline of Common Features
4. What is the Difference Between Annelida and Arthropoda
      – Comparison of Key Differences

Key Terms: Animalia, Anneida, Arachnida, Arthropoda, Chilopoda, Crustacea, Diplopoda, Insecta, Hirudinea, Oligochaeta, Polychaeta

What is Annelida

Annelida refers to a phylum of kingdom Animalia, consisting of segmented worms with elongated body forms. About 9000 species of annelids have been identified so far. Most annelids are aquatic, and some are terrestrial. Annelids are free-living animals with bilateral symmetry. Annelids are triploblastic coelmates that have a true coelom. The coelom is divided by internal septa. That means, annelids have a fully-segmented body called metameric segmentation. The tissues of the body form organs. The three separate sections of the body of an annelid are prostomium, a trunk, and a pygidium. Annelida comprises a complete digestive system with a mouth and anus. The respiration generally occurs through the body surface. The nervous system comprises an anterior nerve ring with ganglia and a ventral nerve cord. Annelids consist of a closed circulatory system with several hearts and blood vessels. The excretion occurs through nephridia. Annelids can be either hermaphroditic or gonochoristic. Internal or external fertilization can occur in annelids. The larval stages of annelids can be zooplanktons.

Figure 1: An earthworm

The three classes of annelids are Polychaeta, Oligochaeta, and Hirudinea. The Polychaeta consists of marine bristle worms. The Oligochaeta consists of aquatic or terrestrial earthworms. The Hirudinea consists of leeches. An earthworm is shown in figure 1. 

What is Arthropoda

Arthropoda refers to another phylum of kingdom Animalia, consisting of animals with jointed appendages and a chitinous exoskeleton. Arthropods can be aquatic, terrestrial or aerial animal forms. Arthropods are triploblastic animals, whose body cavity is a filled with blood or haemolymph. Thus, arthropods are haemocoelomates. Furthermore, the circulatory system of arthropods is an open circulatory system, consisting of a heart and an artery. The body of the Arthropoda is segmented to head, thorax, and abdomen. The head is composed of pairs of antennae and compound eyes. Arthropoda was the first group of animals to develop a head. The jointed appendages can occur in pairs. Since the body of arthropods is covered with a chitinous exoskeleton, they shed their exoskeleton periodically to achieve body growth. This process is called molting or ecdysis. Arthropods consist of a complete digestive system with an anus and mouth. The mouth is modified to chewing or biting. The respiration of arthropods occurs through gills, trachea or book lungs. The excretion of terrestrial arthropods occurs through Malpighian tubules. In aquatic arthropods, the excretion occurs through coxal glands or green glands. The arthropods are unisexual animals.

Figure 2: A bee

The five classes of arthropods are Crustacea (shrimp, crayfish, and lobster), Arachnida (spiders, ticks, mites, and scorpions), Chilopoda (centipedes), Diplopoda (millipedes) and Insecta (bees, butterflies, roaches and beetles). A bee is shown in figure 2. 

Similarities Between Annelida and Arthropoda

• Annelida and Arthropoda are two phyla of the kingdom Animalia.
• Both Annelida and Arthropoda consist of bilateral symmetry.
• Both Annelida and Arthropoda consist of triploblastic animals with three germ layers.
• Both Annelida and Arthropoda have organ system level of organization.
• Both Annelida and Arthropoda consist of segmented body structures.
• Both Annelida and Arthropoda consist of a hydrostatic skeleton.
• Both Annelida and Arthropoda consist of cerebral ganglion with ventral nerve cord.
• Both animals consist of a mouth at one end of the body and the anus in the other end.
• Both animals undergo sexual reproduction, and fertilization can be either internal or external.
• Both animals have similar types of larvae.

Difference Between Annelida and Arthropoda

Definition

Annelida: Annelida refers to an animal phylum that consists of coelomates with elongated, segmented body.

Arthropoda: Arthropoda refers to an animal phylum that consists of haemocoelomates with a segmented body, joint appendages, and chitinous exoskeleton.

Commonly Called

Annelida: Annelids are commonly called segmented worms.

Arthropoda: Arthropods are commonly called animals with jointed legs.

Distinct Head

Annelida: Annelida lacks a distinct head.

Arthropoda: The body of the Arthropoda is differentiated into a distinct head, thorax, and abdomen.

Segmentation of the Body

Annelida: Annelida consists of a fully segmented body, which is called the metameric segmentation.

Arthropoda: Arthropoda does not consist of a fully-segmented body.

Jointed Appendages

Annelida: Annelida lacks jointed appendages.

Arthropoda: Arthropoda consists of joined appendages.

Body Cavity

Annelida: Annelida consists of coelomate animals.

Arthropoda: Arthropoda consists of haemocoelomate animals.

Skeleton

Annelida: Annelida consists of a hydrostatic skeleton.

Arthropoda: Arthropoda consists of both hydrostatic skeleton and exoskeleton.

Circulatory System

Annelida:  Annelida consists of a closed circulatory system.

Arthropoda: Arthropoda consists of an open circulatory system.

Hearts

Annelida: Annelida consists of several, simple hearts.

Arthropoda: Arthropoda consists of one heart.

Senses

Annelida: Annelida consists of antennae, palps, eyes, statocysts, lateral organs, and nuchal organs.

Arthropoda: Arthropoda consists of antennae, statocysts, simple eyes, and compound eyes.

Respiratory Gas Exchange

Annelida: The respiratory gas exchange of the Annelida occurs through the skin or parapodia.  

Arthropoda: The respiratory gas exchange of Arthropoda occurs through gills, trachea or book lungs.

Excretion

Annelida: The excretion of Annelida occurs through nephridia.

Arthropoda: The excretion occurs through coxal gland on malpighian tubules.

Separation of the Sexes

Annelida: Annelida consists of hermaphrodite animals.  

Arthropoda: Arthropoda consists of unisexual animals.

Conclusion

Annelida and Arthropoda are two phyla of the kingdom Animalia, consisting of invertebrates. Both Annelida and Arthropoda share many features. Both are triploblastic animals with bilateral symmetry. Both consist of a segmented body. Both Annelida and Arthropoda consist of a hydrostatic skeleton. But Arthropoda consists of a chitinous exoskeleton. This is the main difference between Annelida and Arthropoda.

Reference:

1.“Phylum Annelida: General Characteristics and Classification.” Online Biology Notes, 10 June 2017, Available here. Accessed 21 Aug. 2017.
2.“General Characteristics and Classification of Arthropoda.” Microbiology Notes, 8 Mar. 2016, Available here. Accessed 21 Aug. 2017.

Image Courtesy:

1.”Regenwurm1″ By Michael Linnenbach – first upload in de wikipedia on 09:58, 16. Feb 2005 by Michael Linnenbach, (CC BY-SA 3.0) via Commons Wikimedia
2. “Bee-apis” By Maciej A. Czyzewski – Own work (GFDL) via Commons Wikimedia

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