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LECTURE Chordata
Major Characteristics found in all chordates:
• Notochord – a stiff but flexible rod along the length of the body
• Dorsal hollow nerve chord – neural structure that develops into the brain and and central nervous system
• Pharyngeal gill slits – openings or grooves found on the cavity behind the mouth (found in all chordates at least at some stage of their life cycle)
• Post-anal tail
1. Eukaryote2. Multicellular3. Bilateral- deuterstomes4. Heterotrophic
General Features Shared by Chordates:
Phylum ChordataSubphylum Urochordata - Tunicates
Class Ascidiacea - Sea SquirtsSolitary e.g. Styela montereyensisColonial - in groups but with own tunicCompound Colonial - colonial with sharedtunic
Class Thaliacea - Salps (free swimming), planktonicClass Larvacea - Gelatinous house, planktonic
Subphylum Urochordata :
Tunicates - ~1400 entirely marine species, including sea squirts.
The name, "tunicate" comes from the firm, but flexible body covering, called a tunic, a leathery outer protective layer
Sessile, filter feeders…
Tunicate - also called 'sea squirt' • notochord is confined to the tail • notochord is lost during metamorphosis into
sessile adult • possess pharyngeal slits • Reproduction- sexual (hermaphroditic) &
asexual (budding)
Subphylum Urochordata = tunicate
Subphylum UrochordataAlthough urochordates are sessile, they typically have motile larvae that truly exhibit all the chordate characteristics…
In a few cases however (i.e. salps); the urochordates retain the larval form even as adults, remaining motile…
Tunicate Adult Anatomy
Class Ascidiacea - Sea Squirts
Class Larvacea (APPENDICULARIANS)-planktonic
Oikopleura
Oikopleura
Jelly-like house
Marine snow
Class Larvacea - Gelatinous house, planktonic
Water flow direction
Emergency exit
• http://planktonchronicles.org/en/episode/larvaceans-their-houses-are-nets/
• The red line shows the water flow (through one entrance) created by the undulating tail of the larvacean. Large particles are blocked by protective grids. The filters on the left, filter tiny organisms from the water which are then passed to the mouth.
https://www.geol.umd.edu/~jmerck/geol431/lectures/03craniata.html
Larvaceans - reproduction
• Larvaceans are entirely sexual in their reproduction, most species are hermaphroditic (each animal is both male and female), but at least one species is gonochoristic (meaning each animal is either male or female).
• In the hermaphroditic species the testis mature before the ovaries thus preventing self fertilisation. The sperm are released into the sea, and then the eggs (ova) are released.
• The release of the ova is by means of rupture of the body wall, thus the animal dies in the process.
Pyrosoma- bioluminescentColonial salp
Class Thaliacea - Salps (free swimming), planktonic
lancet
• Strictly marine• Live buried in sand with head sticking out• Filter feeders
Cephalochordata
Mouth
Cirri
Pharyngeal slitsAtrium
Digestive tract
Atriopore
Segmentalmuscles
Anus
Notochord
Tail
Dorsal,hollow
nerve cord
1 cm
• Lancelets (Cephalochordata) are named for their bladelike shape
• They are marine suspension feeders that retain characteristics of the chordate body plan as adults
Cephalochordata
Fill tunic with Soju!