Blastozoa

fossil echinoderm subphylum

Also known as: blastozoan

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June 22, 2026

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The Blastozoa were an extinct subphylum of echinoderms, related to modern starfish and sea lilies. They existed from the Middle Ordovician to the Late Permian periods, approximately 472 to 251 million years ago.1

Blastoids were sedentary animals anchored to the seafloor by a stem-like column. Their bodies were characterized by a regular structure, with an external skeleton made of calcium carbonate plates arranged in three circles. Some blastoids, like the genus Pentremites, are valuable as index fossils for correlating rock units. The subphylum Blastozoa, proposed in the early 1970s, has gained wide acceptance in scientific classification.12

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echinoderm
Annotated classification
†Subphylum Blastozoa (blastozoans) Cambrian to Permian about 280,000,000–540,000,000 years ago. Stalked echinoderms with soft parts enclosed in a globular theca (chamber) equipped with simple, erect food-gathering appendages (brachioles). †Class Eocrinoidea Lower Cambrian to Silurian about 430,000,000–570,000,000 years ago; body usually
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†Subphylum Blastozoa (blastozoans) Cambrian to Permian about 280,000,000–540,000,000 years ago. Stalked echinoderms with soft parts enclosed in a globular theca (chamber) equipped with simple, erect food-gathering appendages (brachioles). †Class Eocrinoidea Lower Cambrian to Silurian about 430,000,000–570,000,000 years ago; body usually
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