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!