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Are enclosed in a “tunic” of secreted protein and cellulose-like material
Filter feeders Form and Function The adult form is barrel-shaped and the posterior region is attached to a surface
"tunic" - a transparent body covering made of cellulose
siphons - two holes that project from the body of the tunicate
incurrent siphon - water enters here and passes through the pharynx, where food particles are trapped
excurrent siphon - water exits the tunicate, bringing waste along CEPHALOCHORDATA Lancelets Reproduction GENERAL CHARACTERISTICS Tunicates are hermaphroditic.
asexual reproduction: budding
sexual reproduction: internal fertilization
To avoid self-fertilization, the sperm and eggs of the same tunicate may be designed not to accpet each other, or the sperm may mature before the eggs Notochords are present all throughout their lives
Internal segmentation of muscles and nerves (V-shaped)
Close relatives to fish Form and Function Movement Classes it has three openings:
uses a closed circulatory system
they undergo gas exchange in their pharyngeal slits Ascidiacea - the sea squirts; have a sac-like body (ex: Ciona intestinalis; common name: vase tunicate)
Thaliacea - pelagic tunicates; free-swimming (ex: Pyrosoma atlanticum)
Appendicularia - the larvaceans; retains the tail of its larval form (neoteny - evolution by retaining juvenile traits as an adult) (ex: Fritillaria borealis; common name: oikopleura) like the Urochordata, it is a filter feeder with exactly the same systems only this one has a mouth and smaller atrium
it has a swollen tip at the dorsal but not a brain
uses tentacles for sensory
no hemoglobin in blood FEEDING AND EXCRETION they are filter feeders which is why they have an enlarged pharynx
the excess water from the system is released thorugh atriopore MOVEMENT -they have segmented muscles allowing them to undulate Members of the class Ascidiacea are sessile in their adult stage, while members of classes Thaliacea and Appendicularia are free-swimming.
Larvae are generally free-swimming. Ecology Etymology New Latin cephalo, "head" + Latin chorda, "cord" atrium - a cavity that surrounds the pharynx dorsally and laterally
pharynx - where small particles are filtered out before the water leaves the excurrent siphon
have an open circulatory system invasive species; can crowd out other organisms in the ecosystem
also cause economic damage by growing on fishing nets, docks, and buoys Ecology Reproduction Lancelets are gonochoristic, meaning they can either be male or female.
Lancelets only reproduce sexually. their muscles are very weak so they usually stay buried in the sand EXAMPLES Branchiostoma belcheri
a type of lancelet found in the Philippines Yunnanozoon
an ancient species found as a fossil They're a time machine into the past to see how the first chordates would have looked like and how they lived.