52 |
A Handbook of Biology
5.
The larvae of echinoderms are bilaterally symmetrical while adult
echinoderms exhibit radial pentamerous symmetry (AIPMT 2004)
6.
Important characteristic that hemichordates share with chordates is
pharynx with gill slits (NEET 2017)
PHÝLÜM ÇHØRDÅTÅ
It
includes
animals
with
notochord,
dorsal tubular nerve cord and paired
pharyngeal gill slits. Notochord is a flexible
rod located in the mid dorsal line between
the alimentary canal and the nerve cord
in the embryo.
Differences between Chordata and Non-Chordata
Chordata
Non-Chordata
Notochord is found in the embryonic
stage
Notochord is absent
Central nervous system is dorsal,
hollow and single
Central nervous system is ventral,
solid and double
Pharyngeal gill slits present
Gill slits are absent
Ventral heart
Dorsal heart (if present)
A post-anal part (tail) is present
Post-anal tail is absent
Phylum
Chordata
is
classified
into
3
subphyla:
Urochordata,
Cephalochordata & Vertebrata.
Urochordata
(tunicata)
Cephalochordata
Vertebrata (craniata)
Notochord present
only in larval tail.
Body is covered by
test made up of
tunicin.
Exclusively marine.
Hermaphrodite.
E.g. Ascidia, Salpa &
Doliolum.
Notochord
from
head to tail region
and is persistent
throughout the life.
Fish- like body.
Exclusively marine,
sexes are separate.
E.g. Branchiostoma
(Amphioxus or
Lancelet).
Possess notochord during the
Embryonic period. (NEET 2020)
Notochord is replaced by a
cartilaginous or bony vertebral
column in the adult.
Ventral muscular heart.
Kidneys
for
excretion
&
osmoregulation
Paired appendages (fins or
limbs). E.g. Homo sapiens and
Myxine
