Holothuroidea and Echinoderm phylogeny

Question 1

Holothuroidea morphology

Answer 1

Ossicles very small or absent
Bilateral symmetry - mouth at one end, anus at other
-show slight radial pattern with podia
Mouth surrounded in tentacles - modified podia for feeding (suspension or deposit)
Dorsal surface has smaller podia
Ventral surface the podia are bigger - used in crawling and gripping substrate

Question 2

Holothuroidea defence

Answer 2

Can produce nasty chemicals - form of protection
Produces sticky tubules through anus which can produce toxin - holothurin
Some release their viscera to escape predators - under control of mutable connective tissue (can regenerate viscera)
Pearl fish can live in anus… may cause damage making them parasitic or are not harming - different spp?

Question 3

Holothuroidea respiration

Answer 3

Anus leads to series of canals - respiratory trees

• sucks water into anus where trees expand
• gaseous exchange takes place here
• literally breathes through anus

Question 4

Phylogeny

Answer 4

Crinoids most ancient
Asteroids next branch off
Ophiroids following asteroids
Most derived are echinoids and holothuroids