Distinguishes: 2 clades within protostomes
(Lophotrochozoans & Edysozoans)
Lophotrochozoans – named for feeding apparatus.
Includes flatworms, molluscs, & annelids.
Edysozoans – include nematodes
& arthropods. Both have
exoskeletons that must shed in
order to grow. Moulting process
Both represent hypothesis for key events in
the evolutionary history that led to animal
phyla on earth..
“The animal kingdoms great
diversity arose through the process
of evolution, & all animals exhibit
features reminiscent of their
Compare placement of Annelids,
Arthropods, & Molluscs & how they differ:
Morphology based tree:
Annelids & Arthropods
hypothesized to be more
closely related to each other
than molluscs, largely based
on segmented bodies.
Molecular based tree:
Arthropods are separated from both Annelids &
Molluscs & are placed in Ecdysozoans clade.
TERMS TO KNOW Anterior: Pertaining to the front, or head, of a
bilaterally symmetric animal. Posterior: Pertaining
the rear; or tail of a bilaterally symmetric animal.
Dorsal: Pertaining to the back of a bilaterall