Lecture 16: Deuterostomes and Chordates Flashcards
Deuterostomes: two major classes
Echinoderms
Chordates
Echinoderms
Invertebrates such as sea stars and sea urchins
Chordates
Vertebrates such as fish, reptiles and mammals as well as some invertebrates
Chordata members
- Members of Deuterostomia with four derived traits
- Invertebrates (lancelets and tunicates) as well as all vertebrates
Members of Deuterostomia with four derived traits
- Notochord
- Dorsal, hollow nerve cord
- Pharyngeal slits or clefts
- Muscular, post-anal tail
Notochord
- A longitudinal, flexible rod found between the digestive tube and the nerve cord
- Skeletal support for the body
- NOT a calcified-hardened ‘skeleton’
In vertebrates, the backbone develops around the
embryonic notochord
* In many species the backbone almost completely replaces the notochord
* In humans, embryonic notochord reduces and becomes part of the intervertebral discs
Dorsal, hollow nerve cord
- Nerve cord of chordate embryo develops from a specific surface of the ectoderm (neural plate) that rolls and internalizes into a neural tube
- Neural tube is dorsal to the notochord
- The nerve cord of the vertebrate develops
into the brain/spinal cord - Other animal phyla has a solid nerve cord that are, in many cases, ventral
Pharyngeal slits or clefts
- Pharynx: Region just posterior to the mouth (i.e., towards the back of the mouth)
- Pharyngeal clefts: Chordate embryos has arches and grooves that forms along the outer surface of the pharynx
For some chordates, pharyngeal clefts develop into
pharyngeal slits
* Allow water to pass through the body without passing through the entire digestive tract
* Feeding for may invertebrate chordate
* Develops into gill slits of fish
Pharyngeal clefts do not develop into
open slits/gills in adult tetrapods
In humans, pharyngeal clefts differentiate and
form various muscle, nervous and skeletal tissues around the face and neck
Muscular, post-anal tail
- Chordates have a muscular tail that extends post anus
- In many species, the tail is greatly reduced/lost during embryonic development
- In contrast, non-chordates have digestive tract which extends nearly to the whole length of the body
Lancelets are
invertebrates
Do Lancelets have the features of a Chordate?
- Have all features of a Chordate
- Notochord
- Dorsal, hollow nerve-cord
- Pharyngeal slits
- Post-anal tail
Adult Lancelets have
- Adult has cilia around their mouths
- Adults burrow their tail-ends into sand and use cilia to draw water into their mouths to capture food
Tunicates
- More closely related to vertebrates than lancelets
- Larvae resembles a ‘normal’ Chordate with all four Chordate traits
Tunicates larvae settle and go under what?
- Larvae settles at a suitable location and goes under radical metamorphosis
- Notochord and tail resorbed
- Nervous system degenerates
Tunicates feeding system
Filters water through the enlarged pharynx-slits to get food
Huge diversity in Chordate body
- The four derived traits of Chordates are absent in adults of many members of this clade
- These organisms are still Chordates
- In most cases, the four traits are still observed in the embryos of chordate animals
Human embryo has all four derived features of Chordates. During development:
- Notochord gets replaced by the vertebra
- Nerve chord develops into spinal chord and the brain
- Pharyngeal slits develop into various tissues of face and neck
- Post-anal tail recedes
