CHORDATES
Chordates are animals characterized by the presence of notochord at
some stage during their development. Members possess a hollow
nerve cord and pharyngeal gill slits. The other general characteristic
features of Chordates are as follows:
They are bilaterally symmetrical, triploblastic, and coelomate
with the organ-system level of organization.
 They hold a post-anal tail
 The body includes a closed circulatory system.
 In some members of Phylum Chordata, the notochord is present
only in the larval tail, and in some, it is present throughout their
life from head to tail region.
 Chordates have many sub-divisions and Protochordates are one
of the earliest to evolve.
Phylum Chordata is divided into three subphyla: Urochordata,
Cephalochordata, and Vertebrata.
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 Subphylum – Urochordata
It is also referred to as Tunicata which are marine animals. The
body of these animals is surrounded by a leathery covering (similar
to a tunic, hence the name). Larvae are free-swimming, the
notochord is present only in the tail of larvae and after settling on
the seabed, they get transformed into sessile adults. They are
generally hermaphrodites.
Examples include – Ascidians, Doliolum, Oikopleura, etc.
 Subphylum – Cephalochordata
It mainly consists of small, fish-like marine animals in which the
notochord is extended along the entire body. The animals also have
pharynx, which is large with numerous gill- slits. Members of this
subphylum have separate sexes.
Example include – Amphioxus or lancelet.
 Subphylum – Vertebrata
In this subphylum, the notochord is present in the embryonic stages
and is replaced by a vertebral column in the adult. They have 2, 3
or 4 chambered heart, paired appendages for locomotion and
kidneys for excretion or osmoregulation.
NON-CHORDATES
Non-chordates are animals without a notochord – the rod-like elastic
structure that supports the body. This phylum consists of a small
group of worm-like, marine species with an organ-system level of
organization.
The majority of animal species are invertebrates; one estimate puts
the figure at 97%. Many invertebrate taxa have a greater number and
variety of species than the entire subphylum of
Vertebrata. Invertebrates vary widely in size, from 50 μm (0.002
in) rotifers to the 9–10 m (30–33 ft) colossal squid. Some so-called
invertebrates, such as the Tunicata and Cephalochordata, are more
closely related to vertebrates than to other invertebrates. This makes
the invertebrate’s paraphyletic, so the term has little meaning
in taxonomy.
Members of phylum Porifera, Coelenterata, Ctenophora,
Platyhelminthes, Aschelminthes, Annelida, Arthropoda, Mollusca,
Echinodermata and Hemichordata fall under Non-chordates.
The general characteristic features of Non-Chordates are:
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They are cylindrical, triploblastic, coelomate, or
pseudocoelomate animals.
Respiration in these animals takes place through gills, trachea or
body surface.
Most of the times, sexes cannot be distinguished among the
members.
Modes of reproduction involve sexual and asexual
Fertilization is external, though internal fertilization also occurs
in some species.
The body of non-chordates generally includes an open type
of circulatory system.