Question

Choose the correct answer from the alternate given
The three defining characteristics of chordates are
a. Segmentation, dorsal hollow nerve cord, gill arches or pharyngeal pouches
b. Dorsal hollow nerve cord, notochord, bilateral symmetry
c. Well developed coelom, gill arches or pharyngeal pouches, notochord
d. Gill arches or pharyngeal pouches, dorsal hollow nerve cord, notochord

Answer 1

A chordate is an animal belonging to the phylum Chordata, which is part of the kingdom of the Deuterostomes. In the kingdom of Deuterostomes, species have a distinct feature: their anus grows in early embryonic stages before their mouth.

Complete answer:
A broad variety of species form the phylum Chordata, since it is composed of all vertebrates, which are backbone species, and many invertebrates; organisms that do not have a backbone. There are three Chordata subphylums: Cepahlochordata, Vertebrata, and Urochordata. In general, chordates have bilateral symmetric bodies, although there are a few exceptions, and they share distinct features. Chordates, at least at some stage in their lives, have all these features. These characteristics occur in many cases only during embryonic development.

Pharyngeal Slit- This is used as a philtre in invertebrates while feeding, while it grows into gill arches in vertebrate fish, the purpose of which is to support gills. There are gill slits in human embryos, but they vanish before we are born and the tissue grows in the head and neck into other structures. Generally, in terrestrial vertebrates, the tissue is adapted for different reasons, such as for the jaws and the Eustachian tube connecting the ear to the throat.

Cord of the Dorsal Hollow Nerve - This is a tube formed from nerve fibres that in vertebrates form into the central nervous system, consisting of the brain and spinal cord. The vertebrae, which are the bones that form our backbone, protect this nerve cord. What distinguishes chordates is that the nerve cords in non-chordates are strong and are either ventral or lateral inside the body.

Notochord- This cartilage-made flexible skeletal rod is what gives its name to chordates. The notochord passes between the digestive tube of an animal and its nerve cord and provides body support. It is the precursor to a vertebrate backbone, or spine.

Hence, the correct answer is option (D).

Note: A chordate that belongs to the subphylum vertebrata is the lamprey. In its many larval years, it is a jawless fish that lives as a philtre-feeder, then transforms into a parasitic adult with an oral disc filled with teeth that it uses to latch onto other fish. The adult has external breathing gill slits, a cartilaginous skeleton, a nerve cord and a notochord. For the trapping of food particles in their pharynx, larval lampreys use a mucus-secreting gland.