Cordates Flashcards
(24 cards)
What are the three defining characteristics of all chordates?
Dorsal hollow nerve cord
Notochord
Pharyngeal gill slits
What additional features are often found in chordates?
Muscular post-anal tail
Endostyle or thyroid gland
Complete, regionally specialized gut
Ventral contractile heart
Bilateral symmetry
Which subphylum includes the majority of chordate species?
Vertebrata (~66,000 species)
Which subphyla make up the invertebrate chordates?
Urochordata (Tunicata) and Cephalochordata
What is the function of the notochord?
Provides a rigid yet flexible structure for muscle attachment, allowing lateral movement.
What becomes of the notochord in vertebrates?
It’s replaced or surrounded by cartilage or bone; remnant is the nucleus pulposus in intervertebral discs.
Where are the notochord and nerve cord found in tunicates?
Only in the larval stage; both are reabsorbed during metamorphosis.
What are the three classes of Urochordata?
Ascidiacea
Thaliacea
Appendicularia
What are the three forms of ascidian structure?
Solitary (e.g., Styela, Ciona)
Social (e.g., Clavelina)
Compound (e.g., Botryllus, Aplidium)
What structure covers the body of ascidians?
A test or tunic made of tunicin (a cellulose-like material), protein, and sometimes calcium carbonate.
How do ascidians feed?
Filter-feeding using a pharyngeal basket and mucus net produced by the endostyle.
How do ascidiacea reproduce?
Mostly hermaphroditic; cross-fertilization; lecithotrophic larval stage (tadpole larvae) with notochord.
How do thaliaceans move?
Jet propulsion using circular muscles and ciliary currents.
Name and describe the three orders of Thaliacea:
Pyrosomida – colonial, bioluminescent, tropical
Salpida – chain-forming, swims ventral-side-up
Doliolida – complex life cycle, thick muscle bands
What chordate features are retained in larvaceans as adults?
Notochord and nerve cord (paedomorphosis)
What is the “mucus house” used for?
Filtering food from water; discarded and rebuilt frequently, contributes to marine snow.
What distinguishes cephalochordates from other chordates?
Notochord extends past nerve cord to anterior tip
Notochord is contractile, made of muscle-like cells
Lack specialized head and vertebrae
How do lancelets feed?
Filter feeding via pharyngeal gill slits and mucus net from the endostyle.
What is the function of the hepatic caecum?
Digestive organ for extracellular digestion.
What type of fertilization and development do cephalochordates exhibit?
External fertilization, vertebrate-like neurula stage, free-swimming larvae.
What is Hatschek’s pit hypothesized to be homologous with?
The vertebrate pituitary gland.
What do cephalochordates suggest about vertebrate origins?
Homologous Hox gene expression in the nerve cord suggests the vertebrate brain evolved from the cephalochordate nerve cord.
What early fossil supports chordate ancestry?
Pikaia from the Burgess Shale — shows dorsal nerve cord, notochord, and pharyngeal slits.
What are the inferred characteristics of the ancestral deuterostome?
Bilaterally symmetrical, dorsal hollow nerve cord, and pharyngeal gill slits.
