Examples of Deuterostomy in Animals

Deuterostomy is a developmental mode found in certain animals, where the blastopore (the opening of the developing embryo) develops into the anus. This is in contrast to protostomy, where the blastopore becomes the mouth. In this article, we will explore the concept of deuterostomy and provide several examples of animals that exhibit this developmental mode._

Deuterostomy is a significant developmental mode observed in various animal groups. It is characterized by the formation of the anus from the blastopore during embryonic development. This mode of development has evolutionary implications and is found in diverse organisms across different phyla. In this article, we will explore some examples of deuterostomy in animals.


Echinoderms, a group of marine invertebrates, are perhaps the most well-known examples of deuterostomy. These animals include starfish, sea urchins, sea cucumbers, and brittle stars. During embryonic development, the blastopore develops into the anus, and a second opening called the blastopore becomes the mouth. This unique developmental pattern is one of the defining characteristics of echinoderms.


Chordates, the phylum to which humans belong, also exhibit deuterostomy during their embryonic development. In chordates, the blastopore develops into the anus, while a separate opening called the blastopore becomes the mouth. This developmental mode is seen in all chordates, including fish, amphibians, reptiles, birds, and mammals.


Hemichordates are a group of marine animals that exhibit deuterostomy. They are often considered a link between the invertebrates and the chordates. Hemichordates, such as acorn worms, have a body plan that includes a distinct anterior, collar-like structure called the proboscis, a trunk region, and a posterior region called the collar. During embryonic development, the blastopore becomes the anus, and a separate opening forms the mouth.


Xenoturbellids are a small group of marine worms that were only recently discovered and classified. These animals exhibit deuterostomy, with the blastopore developing into the anus and a separate opening forming the mouth. Xenoturbellids have a simple body plan and are considered to be one of the earliest branching groups within the deuterostomes.


Brachiopods are marine invertebrates that have a bivalve shell and a stalk or pedicle that attaches them to the substrate. They exhibit deuterostomy during their embryonic development, with the blastopore becoming the anus and a separate opening forming the mouth. Brachiopods have a long fossil record and were once much more diverse than they are today.

The Evolution of Deuterostomy: Understanding a Key Branch of the Animal Kingdom

Deuterostomy is a major branch of the animal kingdom, encompassing a diverse group of organisms that includes vertebrates, echinoderms, and hemichordates. The evolution of deuterostomes has been a subject of intense scientific study, as it sheds light on the origins and diversity of many of the most complex and successful organisms on Earth. Here, we will explore the key features and evolutionary history of deuterostomes.

Characteristics of Deuterostomes

Deuterostomes are characterized by several unique features, including:

  • Radial cleavage: During embryonic development, the first few divisions of the fertilized egg occur along a radial, or central, axis. This is in contrast to spiral cleavage, which is seen in other animal groups.
  • Enterocoelous coelom formation: The coelom, or body cavity, of deuterostomes forms from the gut, rather than from the mesoderm. This is in contrast to protostomes, where the coelom forms from the mesoderm.
  • Indirect development: Deuterostomes undergo a complex process of development, involving a larval stage and a metamorphosis to the adult form. This is in contrast to protostomes, which undergo direct development.

Evolutionary History of Deuterostomes

The evolutionary history of deuterostomes can be traced back to the early Cambrian period, around 540 million years ago. The first deuterostomes were likely simple, worm-like creatures, similar to modern-day hemichordates. Over time, deuterostomes evolved into a diverse group of organisms, including the first vertebrates and echinoderms.

Deuterostomes and Vertebrates

The evolution of deuterostomes was a key step in the emergence of vertebrates, as it set the stage for the development of a complex nervous system and a bony skeleton. The first vertebrates, which appeared around 500 million years ago, were likely small, fish-like creatures. Over time, vertebrates evolved into a diverse group of organisms, including amphibians, reptiles, birds, and mammals.

Deuterostomes and Echinoderms

Deuterostomes also gave rise to echinoderms, a group of marine organisms that includes sea stars, sea urchins, and sand dollars. Echinoderms are characterized by their radial symmetry, spiny skin, and complex body structures. They are an important part of the marine ecosystem, playing a key role in nutrient cycling and food chains.

The evolution of deuterostomes was a key event in the history of life on Earth, setting the stage for the emergence of vertebrates and echinoderms. Understanding the biology and evolutionary history of deuterostomes can help us to better understand the diversity and complexity of the animal kingdom, and the processes that drive evolution.


Deuterostomy is a fascinating developmental mode observed in various animal groups. From echinoderms to chordates, hemichordates to xenoturbellids, and brachiopods, these examples showcase the diversity of organisms that exhibit deuterostomy. Understanding the different modes of development in animals provides insights into their evolutionary history and relationships. By studying these examples, we can gain a deeper appreciation for the complexity and diversity of life on Earth.

Keywords: deuterostomy, blastopore, anus, mouth, echinoderms, chordates, hemichordates, xenoturbellids, brachiopods, embryonic development, evolutionary history, animal groups, marine invertebrates.

Frequently Asked Questions about Deuterostomy

1. What is deuterostomy?

Deuterostomy is a mode of animal development in which the blastopore, the opening formed during gastrulation, becomes the anus. It is one of the two major developmental modes found in animals, the other being protostomy.

2. How does deuterostomy differ from protostomy?

In deuterostomy, the blastopore develops into the anus, and a new opening called the mouth forms later. In protostomy, the blastopore becomes the mouth, and the anus develops at a different location. These developmental differences have implications for the organization of body cavities, the formation of organs, and other aspects of animal anatomy.

3. Which animal groups exhibit deuterostomy?

Deuterostomy is observed in several animal phyla, including:

  • Echinoderms (e.g., starfish, sea urchins)
  • Chordates (e.g., vertebrates, including mammals, birds, reptiles, amphibians, and fish)
  • Hemichordates (e.g., acorn worms)

4. What are the evolutionary implications of deuterostomy?

Deuterostomy played a significant role in animal evolution. It allowed for the development of complex body plans and the evolution of specialized organ systems. Deuterostomes, particularly chordates, gave rise to a diverse range of animals, including humans. The evolution of deuterostomy also influenced the development of other traits, such as the presence of a coelom (body cavity) and radial symmetry in echinoderms.

5. What are the advantages of deuterostomy?

Deuterostomy provides several advantages for animals, including:

  • Efficient digestion: By having a separate anus and mouth, deuterostomes can develop specialized digestive systems that allow for more efficient processing of food.
  • Continuous feeding: Deuterostomes can feed continuously without interrupting the flow of food through the digestive system, as the mouth is not involved in waste elimination.
  • Greater body plan complexity: Deuterostomy allows for the development of complex body structures and specialized organs, contributing to the diversity and adaptability of deuterostome animals.

6. Are there any examples of deuterostomes that do not exhibit strict deuterostomy?

Yes, there are some exceptions to strict deuterostomy. In some deuterostomes, such as certain echinoderms, the blastopore initially forms the anus but later develops into a second opening that functions as both the anus and mouth. This phenomenon is known as secondary mouth formation or enterocoely. However, these cases still exhibit key aspects of deuterostomy in their developmental processes.

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