Vertebrates

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The notochord is a longitudinal, flexible rod between the digestive tube and nerve cord.

It provides skeletal support throughout most of the length of a chordate.

In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord.

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Dorsal, Hollow Nerve Cord

The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord.

The nerve cord develops into the central nervous system: the brain and the spinal cord.

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Pharyngeal Slits or Clefts

In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body.

Functions of pharyngeal slits:

Suspension-feeding structures in many invertebrate chordates

Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods)

Develop into parts of the ear, head, and neck in tetrapods.

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Muscular, Post-Anal Tail

Chordates have a tail posterior to the anus.

In many species, the tail is greatly reduced during embryonic development.

The tail contains skeletal elements and muscles.

It provides propelling force in many aquatic species.

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Lancelets are named for their bladelike shape. They are marine suspension feeders. Adults retain characteristics of chordate body plan.

Dorsal, hollow

nerve cord

Notochord

Tail

Cirri

Mouth

Pharyngeal slits

Digestive tract

Atrium

Atriopore

Segmental

muscles

Anus

2 cm

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Tunicates (Urochordata) are more closely related to other chordates than are lancelets. They are marine suspension feeders commonly called sea squirts. As an adult, a tunicate draws in water through an incurrent siphon, filtering food particles. Juveniles, not adults, have a notochord.

Tunic

Water flow

Excurrent

siphon

Atrium

An adult tunicate

Pharynx

with

slits

Anus

Atrium

Excurrent

siphon

Incurrent

siphon

to mouth

Dorsal, hollow

nerve cord

Incurrent

siphon

Excurrent

siphon

Muscle

segments

Notochord

Tail

Stomach

Intestine

Intestine

Esophagus

Stomach

Pharynx with slits

A tunicate larva

Slide 13

Fossil of an early Chordate

Segmented muscles

Pharyngeal slits

5 mm

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