Ecdysozoa includes both pseudocoeolmate and coelomate animals.
Formation of a true coelom via schizocoely is currently considered to be derived with respect to formation of a pseudocoelom (persistent blastocoel).
Ecdysozoans undergo ecdysis, the shedding and replacement of the external cuticle as the animal grows.
The main structural component of the cuticle is chitin.
Current Ecdysozoan Phylogeny:
We will visit just a few of these hugely successful animals.
live in aquatic (freshwater and marine) and moist terrestrial environments
lumber around like little, weird bears (according to their discoverer, Johann August Ephraim Goeze, who described them in 1773)
Tardigrades have an amazing ability to survive
physical conditions that would kill any other organism.
extreme heat and cold
nearly 100% desiccation
vaccuum conditions (zero oxygen!)
desiccation for hundreds of years
...don't seem to faze them!
Investigators are studying the tardigrades' amazing abilities to
Discovering their secret could help us learn how to protect mammalian
cells from extreme conditions.
Could discovering the tardigrades'
secrets help us prevent damage to mammalian cells under such extreme conditions?
Maybe we could travel through space and colonize other planets (so we can wreck them, too).
Arthropods inhabit every conceivable environment, from the open
ocean, to the bodies of other animals, plants, and fungi (even your eyelash
follicles, home to Sarcoptes mites that feed on your dead skin).
Their evolutionary relationships have undergone a great deal of revision in the past decades.
The Arthropod Bauplan
protostome coelomate characteristics
internal and external metamerism
fusion of body segments into functional units (tagmosis)
chitinous exoskeleton sometimes fortified
with calcium carbonate (especially in marine crustaceans)
one pair of jointed appendages per each true body segment
many forms have at least one pair of lateral, compound (faceted)
eyes composed of individual photoreceptor units called ommatidia (singular = ommatidium)
coelom is reduced to a gonocoel surrounding the gonads and heart (In what other animals did you see this?)
also like mollusks, the main body cavity is a hemocoel, part of the open circulatory system (In what other animals did you see this?)
Muscles striated and arranged in segmental bands linking the
plates of the exoskeleton for highly efficient locomotion
Development and metamorphosis (changing from juvenile to adult
form) may be
Arthropods (and other animals) that undergo direct development do not
have a free-living larval form. Rather, the parent animals care for
the babies, usually by brooding or encapsulating them (in eggs), and
the young have the same form as the adult, but smaller. A small
version of the adult is sometimes called a nymph.
Arthropods (and other animals) undergoing complete development
have larvae that looks distinctly different from the
adult, and which must undergo a distinct change in morphology from larva to adult.
Arthropods (and other animals) that undergo mixed development brood or
encapsulate the zygotes in eggs, which hatch as larvae with a form
somewhat--but not drastically--
different from that of the adult.
Subsequent metamorphic changes generate the fully adult form.
(Note: an aquatic nymph larva--like that of a dragonfly or damselfly--is called a naiad)
What are the relative advantages of each of these types of