M18 Non-Vertebrate Chordates

Question 1

Phylum chordata sub-phyla

Answer 1

-Craniata (vertebrates)
-Cephalocordata (lancelets)
-Urochordata (or Tunicata, tunicates sea squirts)
-Hemichordata (acorn worm, not a chordate)

Question 2

Cephalocordata

Answer 2

33 species
-10cm long, lancelets
-Morphology, body fishlike (no paired fins, no differentiated head/paired sense organs)
-Free-living, benthic filter feeders with buccal cirri (marine)
-Bilateral symmetry
-Chordate characteristics typified by; hollow dorsal nerve cord, notochord, pharyngeal slits, post-anal tail
-Closest relatives are urochordates/tunicates

Question 3

Urochordata (tunicates)

Answer 3

-Body enclosed in a tunic
-Sessile or free living, solitary or colonial filter feeders. U-shaped gut and large pharynx, separate anus.
-Bilateral symmetry, no specialised organs of gas exchange, excretion or osmoregulation.
-Tunicates have notochord during early development, then lost by metamorphosis.

Question 4

3 tunicate classes

Answer 4

-Ascidiacea (2000 species, sea squirts). Only larvae have chordate characteristics Metamorphosis to sessile, adult, filter-feeder (inhalant and exhalant siphon). Heart with a two-way pump, green blood (high levels of vanadium and cells called vanadocytes, unknown function). Solitary or colonial.

-Thaliacea (70 species, pelagic tunicates/salp). Solitary or colonial, sexual/asexual reproduction (budding).

-Appendicularia (20 species, larvaceans). Planktonic lifestyle retained larval features (retain large tail with notochord as adults). All solitary, sexual reproduction. Can secrete a gelatinous house involved in filtration.