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In barnacle
Burrowing barnacles (order Acrothoracica, about 30 species) are small, unisexual forms that lack shells and have fewer than six pairs of cirri. They burrow into hard limy material, such as clam shells and coral. Trypetesa is found only inside snail shells occupied by hermit crabs.
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In cirripede: Diversity and distribution
…the Acrothoracica are known as burrowing barnacles because they burrow into calcareous substrates (e.g., limestone, corals, and mollusk shells). The acrothoracicans are recognized as fossils primarily by their burrows, and, while their record extends back into the Devonian Period, they are particularly well represented in the Cretaceous Period, when they…
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In cirripede: Annotated classification
Superorder Acrothoracica (burrowing barnacles)Devonian to present; globular in shape; generally without conspicuous calcareous exoskeleton; posterior cirri concentrated at end of trunk; widely distributed in coralline seas, most primitive members in deep sea; approximately 1 mm in length. All 30 species parasitize cnidarians or echinoderms.Superorder Thoracica…
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