Lancelets, Tunicates & Sea Squirts
Lancelets, Tunicates & Sea Squirts
Key Characteristics
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Deuterostome – possessing a notochord
Includes the subphyla Vertebrata
 Mammals
 Fishes
 Amphibians
 Reptiles
 Birds
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Tunicata – salps, sea squirts
Cephalochordata – lancelets
Tunicates and lancelets do
not have any back bone
Anatomy
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Oral Siphon
Atrial Siphon
Notochord – flexible
rod of tissue
Dorsal nerve chord
Pharyngeal slits
Digestion
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Suspension feeders
Filtering through siphon
 Incurrent – takes in water
and food
 Excurrent – expels
wastes
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Pharyngeal slits
Action of cilia passes
food
Esophagus and anus
opening
Respiration
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No respiratory system
Lancelets breathe through their skin
Their skin consists of a simple
epithelium
Little respiration occur in the gill slits
They have no blood
cells like regular fish
Internal Transport
Digestive tube running from
mouth to anus
 Communal vascular system
 Pharyngeal slits – serve as
feeding structures
 Can serve as respiratory
structures
 Takes place along external
body surfaces
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Response
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Elaborate systems that allow them to
respond to stimuli in their environment
Relatively simple nervous system
Do not have specialized sensory
organs
Lancelets have a hollow brain and
small eyespots that detect light
Sensory cells in tunicates may help
control water passing through the
pharynx
Movement
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Rod-like structure in tail called
notochord
A part of the tails musculature
Allows the Tunicate Larvae to
swim more efficiently
Only the Larvae retain the
tadpole shape of the tail
Notochord is only found
in the Larvae
Reproduction
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Sexual reproduction
Two sexes in each species
Sperm and egg are released
into the water
Fertilization occurs
Can reproduce asexually
Examples
Lancelet
Tunicate
Sea Squirt
Facts
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There are 60,000 living
species of chordates
There are about 30
lancelet species
Around 896 – 900
million years old
Lancelets can grow up
to about 2.8” long
Sea Squirts can get up
to 3.9” in size
Literature Cited
http://en.wikipedia.org/wiki/Chordate
 http://www.cliffsnotes.com/study_guide/
Chordata.topicArticleId-8741,articleId8694.html
 http://en.wikipedia.org/wiki/Lancelet
 Biology Book
 http://www.mcwdn.org/Animals/Chordate
.html
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