General characteristics of Cephalochordata
The sub-phylum
Cephalochordata comprises a single class, Leptocardii, which includes only one
family: Branchiostomidae. This family contains two genera: Branchiostoma and
Asymmetron. Initially described by Pallas, these organisms were named Umax
lancealatus and classified within Mollusca. In 1834, Costa identified their
chordate characteristics, and in 1836, Yarrell renamed them Amphioxus. Later,
some specimens were reclassified under the genus Asymmetron, distinguishing two
genera. General characteristics of Cephalochordata can be discussed in the
following two head -
Chordate
Features of Cephalochordata (Amphioxus)
1.
Dorsal
Tubular Nerve Cord: Cephalochordates possess a dorsal
tubular nerve cord.
2.
Notochord:
They have a long notochord extending from the anterior to the posterior end
along the dorsal side. This notochord reaches the cephalic region, hence the
name Cephalochordata.
3.
Gill
Slits: Gill slits are present in the pharynx.
4.
Post-anal
Tail: A post-anal tail is a distinctive feature.
5.
Liver
Diverticulum: Cephalochordates have a liver
diverticulum.
6.
Hepatic
Portal System: They exhibit a developed hepatic portal
system.
7.
Myotomes:
Myotomes are present and aid in locomotion.
8.
Fins:
Dorsal, caudal, and ventral fins are present.
Primitive
Characters of Cephalochordata
1.
Excretory
System: The excretory system contains protonephridia.
2.
Solenocytes:
Unlike other chordates, Amphioxus has solenocytes associated with the
nephridium.
3.
Heart
and Kidneys: Cephalochordates lack a heart and
kidneys.
4.
Paired
Limbs or Fins: There are no paired limbs or paired
fins.
5.
Distinct
Head: Cephalochordates do not have a distinct head.
6.
Sense
Organs: They lack distinct paired sense organs.
7.
Gonads:
Their gonads are without gonoducts.
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