Lecture 18 Flashcards
Chordata - Tunicates & Cephalochordates
What are the five classic chordate characteristics?
Notochord, dorsal hollow nerve cord, pharyngeal pouches and slits, endostyle or thyroid gland, and postanal tail.
What is a notochord?
A rodlike, semirigid tissue enclosed in a sheath that extends the length of the body, lying between the gut and the nervous system, providing skeletal support.
Q: What is the dorsal hollow nerve cord?
A nerve cord found dorsal to the digestive tract in chordates, which becomes the brain at the anterior end through neurulation.
Q: What happens to the notochord in most vertebrates?
In non-vertebrate chordates and jawless vertebrates.
Q: how is the dorsal hollow nerve cord formed?
Via neurulation from the ectoderm
What is the function of pharyngeal pouches and slits in chordates?
In non-vertebrate chordates, they function as a filter-feeding apparatus. In some vertebrates, they develop into structures such as the auditory tube and gills.
What is the earliest known chordate?
Pikaia, from the Burgess Shale, dating back to 510 million years ago.
What is the endostyle?
A longitudinal ciliated groove in the pharynx that secretes mucous for food capture in filter-feeding chordates. It is homologous to the thyroid gland in vertebrates.
What is the postanal tail?
A tail that extends beyond the anus and provides motility in larval tunicates and Amphioxus, and is more efficient in fishes but vestigial in later lineages.
What is Subphylum Cephalochordata?
Metaspriggina walcotti and Haikouella, which showed features like a notochord, pharynx, and dorsal nerve cord.
What is Subphylum Urochordata?
Also known as “tail chordates,” they include tunicates and are mostly sessile as adults. They exhibit chordate characteristics in their larval stage.
What are sea squirts?
Members of Class Ascidiacea, they are filter feeders with an excurrent and incurrent siphon, often forming colonies or living solitarily.
What are the three classes within Subphylum Urochordata?
Ascidiacea (sea squirts), Thaliacea (salps), and Appendicularia (larvaceans).
What are salps?
Free-swimming members of Class Thaliacea, they use jet propulsion for locomotion and filter-feed using a mucus net.
What are larvaceans?
Tiny, pelagic members of Class Appendicularia that retain all five chordate characteristics as adults and secrete a mucous house for suspension feeding.
