Oct 15, 2026 · 7 min · 8 segments
Continuing our study of the echinoderms, let's take a look at their body systems, especially the water vascular system and endoskeleton. What else can we say about their general anatomy and…
In the previous tutorial, we went over some general information regarding phylum Echinodermata.
Echinoderms generally have an endoskeleton, coelom, water vascular system, digestive system, hemal system, nervous system, and reproductive system.
Echinoderms, like the chordates, have an endoskeleton, but their endoskeleton is very different from ours.
The echinoderm endoskeleton is directly beneath the epidermis and is comprised of small calcium-rich plates known as ossicles that are bound together by a unique form of connective tissue known as catch collagen, that the echinoderm can neurologically change from a liquid to a solid state, allowing the echinoderm to assume different postures without muscular effort.
Spines and tubercles project from the ossicles to form the echinoderm's rough and spiny surface.
The coelom of an echinoderm is a fluid-filled chamber that circulates fluids around the body cavity and into the papulae for gas exchange and waste excretion.
Meanwhile, the echinoderm water vascular system comprises a second coelomic compartment made up of a series of canals and numerous tube feet that, when paired with the dermal ossicles of the endoskeleton, and often the major porite, create a hydraulic system that aids in locomotion and feeding.
In some species, like the sea stars, it is the primary mode of locomotion, while others, like the brittle stars, have tube feet on their underside, but lack suction cups, so they are not used for locomotion.
They do this by using muscular pressure to push coelomic fluid into the tube feet to stiffen them for walking, and the internal ampulla that connects to each foot acts as a fluid reservoir.
Contraction of muscles in the ampulla forces water into the tubes, and valves prevent backflow.
For example, many sea stars are carnivorous and feed by everting their stomachs, beginning to digest their prey externally.
Others, like many brittle stars, eat prey whole, while many urchins eat plant matter with self-sharpening teeth, and crinoids are mostly filter feeders.
Regardless of the feeding strategy, food enters the digestive system through the mouth and moves through a short esophagus to a large stomach, often located in the central disc.
From there, a short intestine leads to the intestinal caeca, and any undigested food passes out through the anus.
In the sea cucumbers, the intestine is long and runs most of the length of the body, ending in a large anus, which is sometimes inhabited by other animals.
Gas exchange and respiration instead occurs through the tube feet and papulae in starfish, genital bursae in brittle stars, peristominal gills in sea urchins, and cloacal trees in sea cucumbers.
The echinoderm nervous system is radial and consists of a modified nerve net of interconnecting neurons and no central brain.
In the previous tutorial, we went over some general information regarding phylum Echinodermata.
Echinoderms generally have an endoskeleton, coelom, water vascular system, digestive system, hemal system, nervous system, and reproductive system.
Echinoderms, like the chordates, have an endoskeleton, but their endoskeleton is very different from ours.
The echinoderm endoskeleton is directly beneath the epidermis and is comprised of small calcium-rich plates known as ossicles that are bound together by a unique form of connective tissue known as catch collagen, that the echinoderm can neurologically change from a liquid to a solid state, allowing the echinoderm to assume different postures without muscular effort.
Spines and tubercles project from the ossicles to form the echinoderm's rough and spiny surface.
The coelom of an echinoderm is a fluid-filled chamber that circulates fluids around the body cavity and into the papulae for gas exchange and waste excretion.
Meanwhile, the echinoderm water vascular system comprises a second coelomic compartment made up of a series of canals and numerous tube feet that, when paired with the dermal ossicles of the endoskeleton, and often the major porite, create a hydraulic system that aids in locomotion and feeding.
In some species, like the sea stars, it is the primary mode of locomotion, while others, like the brittle stars, have tube feet on their underside, but lack suction cups, so they are not used for locomotion.
They do this by using muscular pressure to push coelomic fluid into the tube feet to stiffen them for walking, and the internal ampulla that connects to each foot acts as a fluid reservoir.
Contraction of muscles in the ampulla forces water into the tubes, and valves prevent backflow.
For example, many sea stars are carnivorous and feed by everting their stomachs, beginning to digest their prey externally.
Others, like many brittle stars, eat prey whole, while many urchins eat plant matter with self-sharpening teeth, and crinoids are mostly filter feeders.
Regardless of the feeding strategy, food enters the digestive system through the mouth and moves through a short esophagus to a large stomach, often located in the central disc.
From there, a short intestine leads to the intestinal caeca, and any undigested food passes out through the anus.
In the sea cucumbers, the intestine is long and runs most of the length of the body, ending in a large anus, which is sometimes inhabited by other animals.
Gas exchange and respiration instead occurs through the tube feet and papulae in starfish, genital bursae in brittle stars, peristominal gills in sea urchins, and cloacal trees in sea cucumbers.
The echinoderm nervous system is radial and consists of a modified nerve net of interconnecting neurons and no central brain.
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