The subphylum - Cephalochordata
includes Amphioxus or
Branchiostoma.
1., Pallas described this animal first.
He named it as Umax lancealatus, He
included this in Mollusca.
2. In 1834, costa described its
chordata features.
3. In 1836, Yarrel named it as
Amphioxus.
CHORDATE FEATURES OF
CEPHALOCHORDATA (AMPHIOXUS):
1. Presence of dorsal tubural nerve
cord.
2. Presence of a long notochord
from anterior end to posterior end
on the dorsal side. Because, it
extends to the cephalic region.
Hence it is called Cphalochordata.
3. Gill silts are present in the
4. Presence of post anal tail.
5. The presence of liver diverticulum.
6. The development of hepatic portal
system.
7. Presence of Myotomes and which
are useful for locomotion.
8. The presence of dorsal, caudal
and ventral fins.
In these characters
Cephalochordata resembles
chordates.
CEPHALOCHORDATA PRIMITIVE
CHARACTERS:
1. The excretory system contains
protonephrldia.
In the chordate world, the presence
of solenocytes is not report-ed. But,
in Amphioxus solenocytes are
associated with Nephridium)’
2. Absence of heart and kidney.
3. Absence of paired limbs or paired
fins.
4. Absence of distinct head.
5. Absence of distinct paired sense
organs.
6. Gonads are without gonoducts.
Thus cephalochordates will show
many primitive characters
SPECIAL CHARACTERS
OFCEPHALOCHORDATA:
1. Because of its ciliary mode of
feeding, the pharynx is elaborated
with many gill slits. .
2. Oral hood is well developed for
ciliary mode of feeding.
3. Because of its ciliary mode of
feeding the atrium is very well
developed.
Thus, Amphioxus shows some
special characters which are
developed because of its ciliary
mode feeding.
CEPHALOCHORDATES
RELATIONSHIP WITH
UROCHORDATES:
Cephalochordates show many close
relationship with urochordata.
In some points they differ
Similarities:-
1. Presence of gill slits In pharynx.
2. Presence of Endostyle in Pharynx.
3. Presence of Ciliry mode of
Feeding.
4. Presence of atrium.
Difference. :
1. Absence of test.
2. Absence of distinct heart
3. Presence of notoçhord and
nervecord in the adults.
4 Presence of Myotomes in the
adult.
In this way Cephalochordates differ
with Urochordates.
Cephalochordates show some
invertebrate features,
They are,
1. Presence of paired nephridia like
annelids.
2. Presence of flame cells like
Helminths.
3. Presence of soft body and slug
like appearance like molluscans.
By considering the above facts we
come to a conclusion that
Amphioxus is a chordate animal.
Amphioxus is a degenerate jawless
chordate animal. It mainly shows
chordate features. It differs from
urochordates in some aspects.
Hence, It is separated and kept in a
separate sub phylum called
Cephalochordate.

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