60: Animal evolution before vertebrates Flashcards
What does Phylum Chordata encompass?
Vertebrates and their kin, characterized by having a notochord at some developmental stage.
Which organisms are included in Phylum Echinodermata?
Marine organisms like sea stars, sea urchins, and sea cucumbers.
What does Phylum Hemichordata consist of?
Acorn worms and graptolites.
What creatures are in Phylum Xenoturbellida?
Worm-like creatures with simple structures.
What is the notochord in chordates?
A flexible rod along the dorsal side of the gut, present at some stage in all chordates.
What happens to the notochord in adult chordates?
It provides embryonic support and is replaced by vertebral disks in adults, remaining as intervertebral disks.
What is the function of the dorsal nerve cord in chordates?
It develops beneath the dorsal surface and differentiates into the brain and spinal cord post-gastrulation.
What is the role of pharyngeal slits in chordates?
They connect the pharynx to the exterior and are functional as gills in aquatic chordates, present in embryonic stages of terrestrial animals.
How does the postanal tail develop in chordates?
It extends beyond the anus during embryonic development and regresses to become the coccyx (tailbone) in humans.
What is segmentation in chordates evident in?
The arrangement of muscles and vertebral columns.
How did the thyroid gland evolve in chordates?
From a ventral groove in the pharynx of primitive chordates, and in vertebrates, it develops into the thyroid gland, regulating metabolism and growth.
What is the origin of neural crest cells?
Cells derive from the lateral edges of the neural plate during neurulation.
How are neural crest cells formed?
These cells form the neural folds, which then produce the neural crest between the neural tube and epidermis.
What influences the functionality of neural crest cells?
Molecular signals from adjacent mesoderm and ectoderm.
What do neural crest cells become and what do they migrate into?
Neural crest cells become mesenchymal, migrate ventrally, and differentiate into:
- peripheral nervous system ganglia
- pigment cells
- adrenal medulla
- various endocrine tissues
- cartilages of the visceral skull.
What does the axial mesoderm form?
The notochord.
Where is the paraxial mesoderm located and what does it form?
Adjacent to the notochord and neural tube, subdivides into somites as neurulation progresses.
What are the two layers of the lateral plate mesoderm?
Visceral (Splanchnic) Mesoderm (inner layer) and Parietal Lateral Mesoderm (outer layer).
What are the functions of the lateral plate mesoderm?
Lines the body cavity, develops into the circulatory system, forms smooth muscles of the digestive tract, and contributes to the bulk of the connective tissue.
What does each somite divide into?
Dermatome, Myotome, and Sclerotome.
What is the function of the dermatome in somite subdivision?
Forms the dermis of the dorsal part.
What is the function of the myotome in somite subdivision?
Develops into skeletal muscles.
What is the function of the sclerotome in somite subdivision?
Generates the vertebrae and ribs.
What is the monophyletic origin of chordates?
Chordates derive from a single common ancestor.
