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Classifying an Unfamiliar Invertebrate by Body-Plan Criteria

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This procedure classifies an unfamiliar invertebrate specimen by applying germ-layer count, coelom type, and developmental pattern criteria from this unit in fixed sequence.

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Classifying by adult body form instead of these embryonic criteria is the error — judging the specimen by superficial resemblance to a phylum ignores the germ-layer, coelom, and developmental evidence that actually determines its placement.