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Questions and Answers
Which of the following is NOT a characteristic of chordates?
Which of the following is NOT a characteristic of chordates?
The coelom in deuterostomes forms by a process called schizocoely.
The coelom in deuterostomes forms by a process called schizocoely.
False (B)
What is the primary function of the notochord in chordates?
What is the primary function of the notochord in chordates?
The notochord provides structural support and flexibility to the body.
The ______ is a glandular groove located on the floor of the pharynx in simple chordates, and it is homologous to the thyroid gland in vertebrates.
The ______ is a glandular groove located on the floor of the pharynx in simple chordates, and it is homologous to the thyroid gland in vertebrates.
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Which of the following groups are considered deuterostomes?
Which of the following groups are considered deuterostomes?
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The dorsal hollow nerve cord in chordates is derived from the mesoderm.
The dorsal hollow nerve cord in chordates is derived from the mesoderm.
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What is the difference between the endostyle and the thyroid gland?
What is the difference between the endostyle and the thyroid gland?
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Match the following chordate groups with their defining characteristics:
Match the following chordate groups with their defining characteristics:
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Pharyngeal slits are a synapomorphy of chordates.
Pharyngeal slits are a synapomorphy of chordates.
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The process of filter feeding in ancient invertebrates was facilitated by ______.
The process of filter feeding in ancient invertebrates was facilitated by ______.
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What is the significance of the different lifestyles between adult and larvae hemichordates?
What is the significance of the different lifestyles between adult and larvae hemichordates?
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Which of the following is NOT a synapomorphy of chordates?
Which of the following is NOT a synapomorphy of chordates?
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Match the following terms with their corresponding descriptions:
Match the following terms with their corresponding descriptions:
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The lack of a fossil record for the transition from protochordates to chordates is attributed to the ______ nature of early chordates.
The lack of a fossil record for the transition from protochordates to chordates is attributed to the ______ nature of early chordates.
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Which of the following provides evidence against the hypothesis that chordates evolved from annelids and arthropods?
Which of the following provides evidence against the hypothesis that chordates evolved from annelids and arthropods?
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The similarities between chordates, annelids, and arthropods are due to homology.
The similarities between chordates, annelids, and arthropods are due to homology.
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The auricularian hypothesis is based on the ______ larvae.
The auricularian hypothesis is based on the ______ larvae.
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Which of the following is NOT a characteristic shared by chordates and echinoderms?
Which of the following is NOT a characteristic shared by chordates and echinoderms?
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The dorsal nerve cord in chordates is believed to have originated from the adoral cilia in their ancestors.
The dorsal nerve cord in chordates is believed to have originated from the adoral cilia in their ancestors.
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What is the name of the evolutionary process that involves the retention of juvenile features in the adult form?
What is the name of the evolutionary process that involves the retention of juvenile features in the adult form?
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Which of the following is a major argument against the auricularian hypothesis?
Which of the following is a major argument against the auricularian hypothesis?
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Match the following structures with their corresponding direction of flow in hemichordates and chordates:
Match the following structures with their corresponding direction of flow in hemichordates and chordates:
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What is the key evolutionary event that led to the development of chordates from a hemichordate-like ancestor?
What is the key evolutionary event that led to the development of chordates from a hemichordate-like ancestor?
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The mouth opening in both hemichordates and chordates is located ventrally.
The mouth opening in both hemichordates and chordates is located ventrally.
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Study Notes
Chordate Origins
- Chordates are a diverse group of animals, including vertebrates.
- They share five key characteristics: notochord, pharyngeal slits, endostyle/thyroid gland, dorsal hollow nerve cord, and postanal tail.
- These characteristics are considered synapomorphies, meaning they are shared derived traits that help define the group.
- Early chordates show a series of evolutionary steps involving larval stages that eventually produced chordates.
- Some chordate-like deuterostomes, like hemichordates, share some of these traits, however, they diverged from the chordate lineage.
- Chordates evolved from an ancestor that was not a chordate, but a group of protochordates.
- Protochordate examples include acorn worms (hemichordates), lancelets (cephalochordates), and tunicates (urochordates).
- The evolution of vertebrates from chordates is associated with several key derived characteristics like a bony cranium, and vertebrae.
- Echinoderms, another deuterostome group, share traits with chordates, suggesting a common ancestry.
Chordate Characteristics
- Notochord: A flexible rod-like structure providing support, derived from mesoderm. In vertebrates, it's largely replaced by the vertebral column during development. In mammals especially, it's reduced to just the nucleus pulposus.
- Pharyngeal Slits: Slits in the pharynx, initially used for filter-feeding in invertebrate ancestors. In fish, they become gills; in some vertebrates, they contribute to structures like the jaw and inner ear.
- Endostyle/Thyroid Gland: A glandular groove in the pharynx of chordates that produces mucus to trap food. In more advanced chordates (like vertebrates), it becomes the thyroid gland, crucial for metabolism.
- Dorsal Hollow Nerve Cord: A hollow nerve cord running along the dorsal side of the body, derived from ectoderm. This is different from the solid nerve cords in some invertebrates.
- Postanal Tail: A tail extending beyond the anus, used for locomotion in some chordates, often prominent in larval stages.
Chordate Groups
- Cephalochordates (e.g., lancelets): Invertebrates, marine, and suspension feeders. They exhibit all chordate characteristics.
- Urochordates (e.g., tunicates): Invertebrates, marine, often exhibit filter-feeding in their adult phase while showing all chordate characteristics during larval stages.
- Vertebrates: Exhibit a wide range of characteristics, with the defining trait being vertebrae, which replace the notochord.
Different Hypotheses about Chordate Origins
- Annelid/Arthropod Hypothesis: Chordates derived from segmented worms, but this is no longer widely accepted. Criticisms focus on different patterns of segmentation and other traits.
- Echinoderm Hypothesis: Chordates and echinoderms share a common deuterostome ancestor. Supporting evidence from embryology (both are deuterostomes) but molecular evidence doesn't completely match this.
- Garstang Hypothesis: Chordate larvae did not transition to an adult status but matured into a new life form. Chordates retain larval traits of their echinoderm ancestors while adults acquire new features unique to the chordates. It suggests paedomorphosis (retention of juvenile traits in adults) as a key evolutionary mechanism. This hypothesis is generally considered less likely due to later evidence against it, especially for the specifics of gene expression.
Competing Hypotheses and Debunked Theories
- Modern evidence, primarily gene expression, has largely ruled out chordate origins from annelids and arthropods and specifically, from echinoderms.
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Description
Explore the fascinating origins of chordates, including their key characteristics and evolutionary relationships with other deuterostomes. This quiz covers important traits such as notochords and the transition from protochordates to vertebrates, providing insights into the diversity and complexity of this animal group.
