Phylum Chordata Flashcards
(41 cards)
Basic characteristics of phylum chordata
- Bilateral symmetry
- A true coelom
- Deuterostome development
- Radial, indeterminate cleavage
- Enterocoelous coelom development
- Metamerism
- Conspicuous Cephalization in some species
Metamerism
Property of having repeated segments
Cephalization
Concentration of sense organs in head region
Enterocoelous coelom development
Mesoderm is formed in which coelom forms from pouches pinched off to form digestive tract.
Unique features of phylum chordata
4 major features - Possession of:
- Notochord
- Dorsal Tubular Nerve Cord
- Pharyngeal Pouches and Gill Slits
- Post Anal Tail
2 minor features - Possession of:
- Endostyle or Thyroid Gland
- Ventral Heart
What is the notochord?
It is a flexible rod-like structure; extending length of body, and skeletal in function.
Composition of the notochord
It is made up of gelatinous matrix surrounded by outer fibrous or inner elastic notochordal sheath.
The only structural feature of protochordates
Notochord
What replaces the notochord in adult vertebrates?
It is completely replaced by vertebral column in adult Vertebrates
Functions of the vertebral column
It:
- protects the spinal cord and nerve cells,
- gives support to the body, and
- serves as point for articulation of muscles
What is the Dorsal tubular nerve cord?
It is a hollow structure located dorsally (at the back). The anterior part later develops into the largest ganglion referred to as the brain.
How is the dorsal tubular nerve cord formed?
The hollow cord is produced by the in-folding of ectodermal cells that are in contact with the mesoderm in the embryo
What is the protective covering bone that covers the brain?
The cranium
The posterior length of the dorsal tubular nerve cord is called…
…the spinal chord
What are pharyngeal pouches and gill slits?
These slits or openings lead from the pharyngeal cavity to the outside. In lower chordates they are used for filter feeding and respiration.
In tetrapods, the pharyngeal pouches give rise to the eustachian tube, middle ear cavity, tonsils, and parathyroid glands
The post-anal tail…
- Extends beyond anus
- Together with the muscles this supports the free swimming movements in lower chordates
- It helps for balancing in many Mammals
- In human beings, it is vestigial (non-functional) and reduced to coccyx
Functions of the endostyle or thyroid gland
- Secretes mucous that traps food particles in pharyngeal cavity
- They secrete iodinated proteins into the body
Classes under Phylum chordata
Subphylum Hemichordata- Lower Chordates
Subphylum Urochordata
Subphylum Cephalochordata
Subphylum Vertebrata
Which subphyla make up the protochordates (first chordates)?
Subphylum Urochordata
Subphylum Cephalochordata
Sub-phylum Hemichordata
- Generally half-chordates (acorn worms)
- A conspicuous dorsal extension of the pharynx forms an anterior buccal tube.
- Body is divided into three parts: Proboscis, collar, and trunk
- Unique larvae called – Tornaria
- Found on the surface or in the mud flats of streams and creeks
- Burrow through sediment and ingest/assimilate nutrients (detritivores)
- Separate sexes
Which sub-phylum of chordates have tornaria?
Sub-phylum hemichordata
Classification of hemichordates
Class Enteropneusta
- e.g. Balanoglossus, Sarcoglossus
Class Pterobranchia
- e.g. Cephalodiscus, Rhabdopleura
Subphylum Urochordata
- Generally called Sea Squirts or Tunicates
- Have a non-living cellulose tunic covering their body
- Most chordate features found in the free-living ascidian larva
- Adult individuals have just one chordate feature, and are sessile filter feeders
- This phenomenon is called Retrograde metamorphosis
Who first coined the word, ‘chordata’? When?
The word chordata was first coined by Balfour in 1880.
