Animal body plans: symmetry, cavities and the deep splits · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.
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Sorting animals by their embryos

Science · Organisms & Life Processes · ages 19-20
Name ______________________   Date ____________

  1. A jellyfish develops ectoderm and endoderm, but no mesoderm. Which term describes its germ layers?

    • Coelomate
    • Triploblastic
    • Diploblastic

  2. An animal has one plane that divides its body into roughly matching left and right halves. What symmetry does it have?

    • Radial symmetry
    • Bilateral symmetry
    • Asymmetrical body plan

  3. In the usual deuterostome developmental pattern, which opening forms at the blastopore site?

    • The anus
    • The mouth
    • The body cavity

  4. A worm has three germ layers. A fluid-filled space between its gut and body wall is completely lined by mesoderm-derived tissue. Which description follows?

    • Diploblastic and coelomate
    • Triploblastic and acoelomate
    • Triploblastic and coelomate

  5. A seabed animal is identified as an echinoderm. Its larvae are bilateral, but its adults are radial. Which interpretation fits?

    • Bilateral ancestry with secondary radial symmetry
    • Radial ancestry with no bilateral developmental stage
    • Bilateral larvae that become asymmetrical as adults

  6. A supported tree puts two streamlined swimmers on separate branches. A reconstruction shows no streamlining in their shared ancestor or in the ancestors at the start of either branch. Which explanation fits this evidence?

    • Both inherited streamlining unchanged from their shared ancestor.
    • Streamlining arose separately in the two descendant lineages.
    • Matching outlines show the tree must join only these swimmers.

  7. A student says any animal whose blastopore becomes its mouth must be a protostome. Which reply best evaluates this claim?

    • Blastopore fate varies; compare other traits and DNA.
    • Blastopore fate never varies; no other evidence is needed.
    • Adult swimming speed settles ancestry; embryo traits cannot help.

  8. In the standard introductory animal tree, a sea urchin shares a more recent common ancestor with a clam than with a fish.

    Circle one:   True   False

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Answer key

For grown-ups. Fold this page away before handing over the rest.

Sorting animals by their embryos W1-mt_hEC72cvFQF-s1

  1. Diploblastic · Ectoderm and endoderm are two germ layers. An animal with two germ layers is diploblastic.
  2. Bilateral symmetry · One plane separating roughly matching left and right halves describes bilateral symmetry.
  3. The anus · In the usual deuterostome pattern, the anus forms at the blastopore site and the mouth forms elsewhere.
  4. Triploblastic and coelomate · Three germ layers means triploblastic. Complete mesoderm-derived lining identifies a coelom. These features alone do not identify the worm's phylum.
  5. Bilateral ancestry with secondary radial symmetry · Echinoderms belong to Bilateria. Their adult radial symmetry evolved within a bilaterian lineage and is called secondary radial symmetry.
  6. Streamlining arose separately in the two descendant lineages. · The stated reconstruction places non-streamlined ancestors before each streamlined lineage. Separate origins of the similar form support convergence.
  7. Blastopore fate varies; compare other traits and DNA. · The usual mouth-at-blastopore pattern has exceptions. It provides developmental evidence but cannot define a lineage by itself.
  8. False · The standard introductory tree groups echinoderms and chordates in Deuterostomia. Clams are protostomes, so the statement reverses the relationship.
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