The Cephalochordata are a small subphylum (about 28 species) of small, 5 to 10 centimetres long. All known species are marine. They occur all around the world in both temperate and tropical waters. Cephalochordates live in shallow marine or brackish water all over the world. They can actively swim around, but most of the time are sedentary, buried in sand.

1. SUBPHYLUM
CEPHALOCHORDATA

2. CEPHALOCHORDATA
• The Cephalochordata are a small subphylum (about 28
species) of small, 5 to 10 centimetres long.
• All known species are marine. They occur all around the
world in both temperate and tropical waters.
• Cephalochordates live in shallow marine or brackish
water all over the world. They can actively swim around,
but most of the time are sedentary, buried in sand.

3. • The dorsal nerve cord is supported by a muscularized
rod, or notochord.
• The pharynx is perforated by over 100 pharyngeal slits
or "gill slits", which are used to strain food particles out of
the water.
• The musculature of the body is divided up into V-shaped
blocks, or myomeres, and there is a post-anal tail.

5. • Body is fish -like and is useful for burrowing and
swimming. It has a head and It shows a tail.
• Appendages are absent.
• Dorsal, caudal and ventral fins are present.
• Body wall shows one cell thick, non-ciliated epidermis,
dermis, connective tissue, striated muscle and parietal
peritoneum.

6. • It has no exoskeleton.
• Notochord extends from the anterior end to posterior end
• Enterocoelic coelom is present. However, it is reduced in
the pharyngeal region . In enterocoely, a mesoderm
(middle layer) is formed in a developing embryo, in which
the coelom forms from pouches "pinched" off of the
digestive tract (also known as the embryonic gut, or
archenteron).

7. • Alimentary canal is long. It includes a large pharynx with
many gill-slits ciliary mode of feeding is developed.
• Respiration is through gills.
• It exhibit closed circulatory system.
• Heart and respiratory pigments are absent.

9. • Hepatic portal system is present.
• The hepatic portal system is the system of veins
comprising the hepatic portal vein and its tributaries. It is
responsible for directing blood from parts of the
gastrointestinal (GI) tract to the liver.
• Excretory system shows paired protonephridia with
solenocytes [an excretory organ consisting of a hollow
cell with branched processes with bunches of beating
cilia in the lumen which maintain a current of liquid].

10. • Brain is not present.Two pairs of cerebral and several
pairs of spinal nerves are present.
• Sexes are separate.
• Asexual reproduction will not take place.Fertilization is
external.
• Cephalochordates reproduce by releasing their eggs and
sperm into the water, where they are fertilized externally.
• The fertilized eggs develop into free-swimming larvae
that drift in the water for up to 200 days, feeding on
plankton and other suspended matter, before settling
down as adults.