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These worm-like organisms have a wide range of body size.
Priapulids are quite small, ranging from about 0.55 millimeters long to about 20 centimeters long.
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The basic body form of a priapulid consists of a trunk, a collar, a caudal appendage,
and an eversible proboscis called an introvert.
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Presoma:
Also known as the proboscis, it is covered by spiny papillae.
The purpose of the spiny papilla is for capturing their prey.
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The smaller priapulids feed on bacteria.
However, the larger species feeds on soft-bodied invertebrates.
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Their mouth is pushed forward, allowing their teeth to consume the prey.
The mouth is described to be retractable.
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When the prey has been captured, the retractor muscles within the mouth
allow the proboscis to retract.
Thus the priapulid is able to pull its prey into its gut.
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Gut:
They have a complete gut, consisting of a mouth and an anus.
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Coelom:
Since little is known about these creatures, the characteristic of a true coelom or a pseudocoelom is still debated.
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Circulatory System:
It is thought that these creatures have no special circulatory system.
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Basics