The key difference between arthropods and annelids is that the arthropods are a group of invertebrates that includes animals having a segmented body, an exoskeleton and paired appendages while annelids are another group of invertebrates that includes segmented worms possessing transverse rings.
Arthropoda and Annelida are two extremely different and important phyla of the Kingdom Animalia. These two phyla differ from each other by many characteristics including taxonomic diversity, body organization, ecological specializations, etc. Basically, phylum Arthropoda contains invertebrates that possess an exoskeleton, a segmented body, and paired jointed appendages while phylum annelids contain segmented worms such as leeches, earthworms, etc. This article provides simplified and summarized information on the difference between arthropods and annelids and finally presents a side by side comparison for better clarification.
CONTENTS
1. Overview and Key Difference
2. What are Arthropods
3. What are Annelids
4. Similarities Between Arthropods and Annelids
5. Side by Side Comparison – Arthropods vs Annelids in Tabular Form
6. Summary
What are Arthropods?
Arthropods are a group of invertebrates that possess an external skeleton, a segmented body, and paired appendages. 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 mostly include diversified insects, crustaceans, arachnids, and other arthropod members. Their segmented body, jointed appendages, and chitinous exoskeleton are the main characteristics that differentiate them from other animals.
The arthropod’s body has three segments or tagma: head, thorax, and abdomen. Furthermore, they possess segmented legs, and their exoskeleton is flexible at the junctions. The exoskeleton (cuticle) is a hard covering composed of chitin. Thus, it gives excellent protection to the animal.
Figure 01: Arthropods
In addition, arthropods possess an open circulatory system in which blood circulates through the body via filling up haemocoels. Arthropods have compound eyes, and they perceive visual sensing through these compound eyes. Most of them have antennae for other means of sensing. Both internal and external fertilization processes are present among arthropods. However, all 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 be never-ending as there are members of microscopic size to several meters long, and they can sustain even with one animal at any place and can grow up to millions with time.
What are Annelids?
Annelids are a large phylum consisting of segmented worms such as ragworms, earthworms, and nuisance leeches. At present, there are over 17,000 extant species of annelids. Usually, they live in freshwater or saltwater as well as around moist terrestrial environments. Annelid has an elongated and segmented body by transverse ring-like constrictions. These constrictions are called annuli, and they are internally segmented or partitioned via septa at the same places as the annuli.
Figure 02: Annelid
Annelids secrete their cuticle from their skin cells. Collagen is the protein that makes the annelid cuticle, and it is not very hard. Many scientists believe that they have capillaries to take blood through organs. However, annelids possess a closed circulatory system. 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 are the Similarities Between Arthropods and Annelids?
- Arthropods and Annelids are two major phyla of Kingdom Animalia.
- Both phyla are composed of organisms with segmented bodies.
- Also, both phyla consist of invertebrates.
- Furthermore, both do not have endoskeletons.
What is the Difference Between Arthropods and Annelids?
Both arthropods and annelids are two groups of invertebrates that belong to kingdom Animalia. They do not possess an endoskeleton. However, the phylum arthropoda consists of animals with a segmented body, an exoskeleton, and paired appendages. Whereas, phylum annelid consists of segmented worms that possess transverse rings. So, this is the key difference between arthropods and annelids. Importantly, a significant difference between arthropods and annelids is that the arthropods have a chitinous exoskeleton while annelids do not have an exoskeleton.
Moreover, arthropods have a chitinous cuticle while annelids have a collagenous cuticle. Besides, annelids are worms and do not have legs, but they have parapodia for locomotion, while arthropods have segmented appendages for locomotion. Therefore, this is also a significant difference between arthropods and annelids. Also, another difference between arthropods and annelids is that annelids usually have a closed circulatory system while it is an open system in arthropods. Moreover, diversity is extremely high among arthropods compared to annelids.
The below infographic summarizes the difference between arthropods and annelids in tabular form.
Summary – Arthropods vs Annelids
Arthropods are invertebrate animals that possess a segmented body, an exoskeleton, and paired appendages. Whereas, annelids are another group of invertebrates that are segmented worms by transverse rings. Though arthropods have an exoskeleton, annelids do not. Furthermore, arthropods have an open circulatory system while annelids have a closed circulatory system. Moreover, arthropods have a chitinous cuticle while annelids have a collagenous cuticle. Insects, crustaceans, arachnids are several groups of arthropods while earthworms, ragworms, and leeches are some groups of annelids. Thus, this summarizes the difference between arthropods and annelids.
Reference:
1.“Arthropod.” Wikipedia, Wikimedia Foundation, 15 Mar. 2019, Available here.
2. Reish, Donald J. “Annelid.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 18 Dec. 2013, Available here.
Image Courtesy:
1. “Arthropoda” By Kolihapeltis 01 Pengo.jpg: Peter HalaszStylonurus BW.jpg: Nobu TamuraSCORPIO MAURUS PALMATUS.jpg: Guy HaimovitchBlue crab on market in Piraeus – Callinectes sapidus Rathbun 20020819-317.jpg: WpoppFemale centipede with eggs.jpg: Marshal HedinJohn Kratz – Swallowtail (by-sa).jpg: John Kratzderivative work: Xvazquez, Amada44 – Kolihapeltis 01 Pengo.jpgStylonurus BW.jpgSCORPIO MAURUS PALMATUS.jpgBlue crab on market in Piraeus – Callinectes sapidus Rathbun 20020819-317.jpgFemale centipede with eggs.jpgJohn Kratz – Swallowtail (by-sa).jpg (CC BY-SA 3.0) via Commons Wikimedia
2. “Nerr0328” By Unknown – (Public Domain) via Commons Wikimedia