Dominic Stone
Echinoderms are exclusively marine animals that include sea stars, sea urchins, sea cucumbers, brittle stars, and sea lilies. Unlike most other animals, they do not have distinct heads and tails and are not bilaterally symmetrical. Echinoderms have a unique water-vascular system that helps them move, feed, and breathe, and they also have tube feet. Echinoderms have muscles, and their muscle regeneration has been studied extensively, particularly in holothurians, which have the most developed muscle systems. Echinoderm muscles can be induced to contract by acetylcholine (ACh), and their muscle tissue exhibits dedifferentiation and myogenesis following injury.
| Characteristics | Values |
|---|---|
| Movement | Echinoderms move using a unique water-vascular system that ends in hundreds of water-filled tube feet. |
| Body structure | Echinoderms are not bilateral, instead, they have five-part symmetry. |
| Body composition | Echinoderms are composed of tiny, hard calcium-based plates that are often spiny and covered by a thin skin. |
| Skeleton | Echinoderms have an endoskeleton, with a firm internal skeleton made of calcium-based plates. |
| Muscle regeneration | Echinoderms have been studied for muscle regeneration, particularly in holothurians (sea cucumbers) due to their well-developed muscle systems. |
| Muscle contraction | Echinoderm muscles can be induced to contract by substances like ACh (acetylcholine) and GABA (gamma-Aminobutyric acid). |
| Muscle structure | Holothurians (sea cucumbers) have a well-developed hemal system with an outer epithelial layer, a circular muscle layer, and an inner connective tissue layer. |
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What You'll Learn
- Echinoderms use a water-vascular system to move, feed and breathe
- Echinoderms have muscles, but they don't use them to move body parts
- Holothurians are the echinoderm group with the most developed muscle systems
- Echinoderms are potential model systems for studies on muscle regeneration
- Echinoderm muscles can be regulated by chemical messengers like ACh and GABA
Echinoderms use a water-vascular system to move, feed and breathe
Echinoderms, such as sea stars, sea urchins, sea cucumbers, and brittle stars, are exclusively marine animals. They have a unique water-based circulatory system called a water vascular system, which they use to move, feed, and breathe. This system is made up of a central ring canal and radial canals extending along each arm. Water circulates through these structures, facilitating gas exchange, nutrient circulation, and locomotion.
The water vascular system projects from holes in the skeleton in the form of tube feet. These tube feet can expand or contract based on the volume of water present in the system, allowing the animal to protrude or retract them using hydrostatic pressure. This enables echinoderms to grip surfaces and grasp prey. For example, sea stars use their tube feet to latch onto opposite halves of a bivalve mollusk, like a clam, and slowly pull the shells apart to expose the flesh within.
Water enters the madreporite on the aboral side of the echinoderm and passes into the stone canal, which moves water into the ring canal. The ring canal then connects to the radial canals, which move water into the ampullae, where the tube feet are located. By moving water through this system, echinoderms can generate slow but powerful movement.
The water vascular system also contributes to echinoderms' ability to feed and breathe. For example, sea stars have two stomachs, one of which can protrude through their mouths to secrete digestive juices onto prey before ingestion, making digestion easier. The water vascular system's role in gas exchange ensures that echinoderms can breathe and maintain adequate oxygen levels in their bodies.
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Echinoderms have muscles, but they don't use them to move body parts
Echinoderms are exclusively marine animals that include sea stars, sea lilies, sea urchins, sea cucumbers, and brittle stars. They have a unique body plan that deviates from the typical bilateral symmetry seen in most animals. Echinoderms possess an internal skeleton (endoskeleton) made of tiny, hard calcium-based plates that are often spiny and covered by a thin skin.
While echinoderms do have muscles, they do not rely on them for moving body parts like many other animals. Instead, they have evolved a specialised water-vascular system for movement, feeding, and breathing. This system consists of hundreds of tube feet that are filled with water, allowing them to move slowly, often appearing nearly stationary by human standards.
The muscle systems of echinoderms have been studied, particularly in the context of muscle regeneration. Holothurians, a type of echinoderm, have the most developed muscle systems and have been the focus of research due to the ease of accessing their body wall muscles for experimentation. Echinoderms have been observed to undergo de-differentiation and myogenesis following injury, evisceration, and amputation, leading to the regeneration of muscle tissue.
Despite having muscles, echinoderms primarily use their water-vascular system for movement and other functions. This system enables them to cling to rocks, bury themselves in sand, and swim in some cases. For example, unstalked crinoids (feather stars) swim by thrashing their numerous arms in a coordinated manner. Echinoderms also exhibit a righting response when overturned, using their tube feet and arms to restore their normal position.
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Holothurians are the echinoderm group with the most developed muscle systems
Echinoderms are a phylum of exclusively marine animals, which include sea stars, brittle stars, sea urchins, sea cucumbers and their relatives. They have a unique water-vascular system, which ends in hundreds of water-filled tube feet, allowing them to move, feed and breathe. This system is used in walking, respiration and feeding. Echinoderms do not have large muscles like many other animals.
Holothurians, or sea cucumbers, are the echinoderm group with the most developed muscle systems. They are the most prominent members of the deep ocean floor, accounting for 90% of its biomass. Holothurians have bilateral symmetry as adults and do not have as much of a skeleton as other echinoderm groups. They have a well-developed hemal system, with the wall of the hemal vessels typically consisting of three layers: an outer epithelial layer, an intermediate circular muscle layer, and an inner connective tissue layer. The hemal vessels do not have obvious linings, and most of the lumen is occupied by connective tissue, forming a network.
Holothurians have been the focus of many studies on muscle regeneration, as their muscles are easily dissected and manipulated. They possess five retractor muscles that pull in the oral complex of organs with tentacles into the body cavity. In addition, some holothurian species can undergo evisceration, where most internal viscera are eliminated following noxious stimuli, followed by a process of regeneration.
The muscle regeneration process in holothurians involves two main events: de-differentiation and myogenesis. De-differentiation occurs early in the regeneration process, during wound healing, and is characterised by the disorganisation of muscle tissue, which can lead to the thinning or disappearance of the muscle layer. Myogenesis, on the other hand, takes place during the regenerative period, once the new tissue is being formed.
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Echinoderms are potential model systems for studies on muscle regeneration
Echinoderms are a phylum of exclusively marine animals that exhibit impressive regenerative capabilities. They are closely related to chordates but are not well-known in the biomedical field. This lack of knowledge has limited their use in studying pharmacological effects on muscle formation and regeneration. However, echinoderms present interesting model systems with high potential for muscle regeneration studies.
Echinoderms have a unique water-vascular system that enables them to move, feed, and breathe. They typically have a five-part symmetry, with tiny, hard calcium-based plates that form an endoskeleton. Their muscle bundles are covered with a continuous basal lamina, giving them a rolled-up sheet-like structure. Echinoderms possess epithelial and myoepithelial cells, which form a pseudostratified myoepithelium anchored to the basal lamina.
The impressive regenerative abilities of echinoderms make them attractive models for understanding muscle regeneration. Echinoderms can regenerate most tissues and organs after injury or self-induced autotomy. Muscle regeneration studies have focused on holothurians, a group with well-developed muscle systems and easily accessible muscles for experimentation. Additionally, holothurian species can undergo evisceration, followed by a regeneration process where internal viscera are replaced.
During muscle regeneration in echinoderms, two key events occur: dedifferentiation and myogenesis. Dedifferentiation happens early in the regeneration process, coinciding with wound healing, while myogenesis is integral to the regenerative period. Microscopy techniques have been employed to study the steps of muscle cell regeneration, revealing species-related differences and conserved processes among echinoderm groups.
In summary, echinoderms are potential model systems for studies on muscle regeneration due to their close phylogenetic relationship to vertebrates, their high regenerative capacities, and the accessibility of their muscle structures for experimentation. By studying echinoderms, researchers can gain valuable insights into the cellular and molecular processes underlying successful muscle regeneration.
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Echinoderm muscles can be regulated by chemical messengers like ACh and GABA
Echinoderms are exclusively marine animals and possess a well-differentiated yet simple muscular system. They do not rely on large muscles for movement, feeding, and breathing like many other animals. Instead, they utilize a unique water-vascular system that ends in hundreds of water-filled tube feet. This system does not produce high-speed movement, and echinoderms are known for their slow and almost stationary rate of movement.
Despite their simple muscular system, echinoderms have a wide range of physiological and behavioral processes, including feeding, reproduction, movement, respiration, and excretion. Their muscle systems can be divided into two main types: somatic and visceral musculature. The somatic musculature typically has a myoepithelial organization, while the visceral musculature contains muscle bundles formed by the aggregation of myocytes.
The myoepithelium is composed mainly of myoepithelial and peritoneal cells, which can be further classified into simple myoepithelium, pseudostratified myoepithelium, bipartite pseudostratified myoepithelium, and stratified myoepithelium. Muscle bundles are formed by the grouping of several myocytes surrounded by basal lamina. These muscle bundles consist mostly of smooth muscle fibers, but obliquely striated muscle fibers are also found in ophiuroids and crinoids.
Echinoderm muscles are regulated by various neurotransmitters, including acetylcholine (ACh) and gamma-aminobutyric acid (GABA). ACh and nitric oxide (NO) are considered the primary excitatory and inhibitory neurotransmitters in echinoderms, respectively. GABA, a classic neurotransmitter, has variable effects on different muscles.
Neuropeptides, such as VP/OT-type neuropeptides, are also known to play a role in regulating muscle relaxation in echinoderms. Odekunle et al. (2019) observed the anatomical expression patterns of the VP/OT-type neuropeptide and its receptor in the starfish *A. rubens*. They suggested that these neuropeptides may indirectly influence muscle relaxation by participating in other neural processes.
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Frequently asked questions
Echinoderms do have muscles, but they don't use large muscles for movement like many other animals. Instead, they have a unique water-vascular system that helps them move, feed and breathe.
Echinoderms have a water-vascular system that ends in hundreds of water-filled tube feet. This allows them to move, albeit very slowly. Some echinoderms, like starfishes, can perform a slow somersault to right themselves when overturned.
Echinoderms include sea stars, sea lilies, sea urchins, sea cucumbers, and brittle stars.
