Difference Between Arthropods and Annelids

Arthropods vs Annelids

Arthropods and annelids are two extremely different and important phyla of the animal kingdom. There are many differences exhibited between these two phyla including the taxonomic diversity, body organization, ecological specializations, and many more. However, certain average persons would have understood that there is no much difference between animals in the two phyla due to lack of or very limited knowledge. This article provides simplified and summarized information about both arthropods and annelids, and finally presents a comparison for a better clarification.

What are Arthropods?

Arthropods are a group of invertebrates, but they are the most diversified group of animals in the entire kingdom with more than 1.17 million extant described species. In addition, more than 80% of the described species are arthropods. They include the mostly diversified insects, crustaceans, arachnids, and other arthropod members. Their segmented body, jointed appendages, and chitinous exoskeleton are the main differentiating characteristics from other animals. The arthropod’s body is segmented or tagmatized mainly into three parts or tagma known as head, thorax, and abdomen. Their legs are composed of segments, and the exoskeleton is flexible at the junctions. The exoskeleton or the cuticle is made up of a protein known as chitin, which is hard and provides an excellent protection for the animals. In arthropods, the blood is circulated through the body via filling up haemocoels, and it is an open circulatory system. Their visual sensing being operated through the compound eyes. Most of them have antennae for other means of sensing. Both internal and external fertilization processes are present among arthropods. However, all the female adults lay eggs after a successful mating with a male. The larval stages become adults after different time intervals following development, and those periods vary across species. As these animals develop, they shed their exoskeleton at many times during their lifetime. Overall, the fascination about these animals would never be ending as there are members of microscopic size to several metres long, and they can sustain even with one animal at any place that can grow up to millions with time.

What are Annelids?

Annelids are a large phylum consisting segmented worms, rag worms, earthworms, and nuisance leeches. There are over 17,000 extant species of annelids presently. Usually, they live in freshwater or saltwater as well as around moist terrestrial environments. The body of an annelid is elongated with segmentation has taken place externally through ring-like constrictions. These constrictions are called as annuli, and they are internally segmented or partitioned via septa at the same places as the annuli. Annelids secrete their cuticle from their skin cells, and the cuticle is made up of collagen, but it is not as hard as in many other invertebrates. Many scientists believe that they have capillaries to take blood through organs, and it is a closed circulatory system in annelids. They usually do not moult their cuticle, but some species shed their skin (leeches) or jaws (polychaetes). Their body cavity is a coelom but some annelid species do not have a coelom and some have it in a very small place.


What is the difference between  Arthropod and Annelid?

• Both arthropods and annelids are invertebrates without endoskeletons, but arthropods have a chitinous exoskeleton, and the body shape is maintained through hydrostatic pressure in annelids.

• Arthropods have a chitinous cuticle while annelids have a collagenous cuticle.

• Annelid are worms, and do not have legs, but they have parapodia for locomotion, while arthropods have segmented appendages for locomotion.

• Annelids usually have a closed circulatory system while it is an open system in arthropods.

• The diversity is extremely high among arthropods compared to annelids.


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    Chitin is not a protein, but polysaccharide.