Phylum Chordata: Subphylum Urochordata

Question 1

Chordate Characteristics (4)

Answer 1

Perforated pharynx
Notochord
Hollow dorsal nerve chord
Muscular post-anal tail

Question 2

Urochordata Characteristics (3)

Answer 2

Tunic (tunicin is cellulose-like fibrous material)
No metamerism
Eucoelom as pericardium (major second body cavity is hemocoel)

Question 3

Asidiacea Tunic

Answer 3

Made of living and non-living tissues
The tunic is never shed, just constantly enlarged and remodelled
Tunicin (cellulose-like) and protein
Hemal channels with blood cells

Question 4

Ascidiacea Colonial Forms (3)

Answer 4

Zooids interconnected by stolons
Zooids arise from a basal mat of shared tunic
Zooids entirely embedded in a shared tunic (sometimes clusters of zooids share atrial siphon)

Question 5

Ascidiacea Sexual Reproduction

Answer 5

Hermaphroditic

Generally broadcast spawn sperm and eggs simultaneously

Question 6

Ascidiacea Larvae

Answer 6

Short-lived, non-feeding, tadpole larvae
Tail with: notochord, hollow dorsal nerve cord, muscles
Attaches to substrate with adhesive papillae, apoptosis of tail and 90-degree rotation of viscera

Question 7

Ascidiacea Feeding

Answer 7

Beating lateral cilia draws water into the buccal siphon and the phytoplankton are trapped by a mucous net created by the endostyle and moved by frontal cilia
The food is moved to the dorsal lamina where it is transferred to the stomach.
The water flows out of stigmata and leaves via the atrial siphon

Question 8

Class Larvacea Characteristics

Answer 8

Holoplanktonic
Pharynx with 2 stigmata
Tail with a notochord, dorsal hollow nerve cord and muscles

Question 9

Larvacea feeding

Answer 9

They secrete a house outside of their body
Pre-filters sift out large particles before entering the house, then pass through finer food-concentrating filters before passing through the body and out excurrent opening
Water current is created by the beating of tail

Question 10

Heterochrony and how it relates to paedomorphosis

Answer 10

If the ancestral state is ascidians then if the rate of sexual maturity became faster than the rate of body growth in the tadpole larva, they would reach sexual maturity before an adult body form is achieved
This would make larvaceans and other chordates paedomorphic

Question 11

Peramorphosis

Answer 11

If ascidian life cycle is derived they represent a terminal addition on the body form and lifestyle of chordates