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What is the largest phylum of the animal kingdom?
- spiral cleavage
- initial pore is forms the mouth
- coelem forms from blocks in mesoderm
Two groups of protostomes
- grow by adding increments to their bodies
- feeding structure called "lophophore" (cilia that help in suspension feeding)
- larvae called "trochophore" (swim and feed using cilia)
grow by molting (sheds cuticle if soft skin, exoskeleton if hard skin)
What are the similarities between the Protostome phyla?
- bilaterally symmetric
- similar embryonic development
What are the differences between the protostome phyla?
- reversion to acoelomate body
- pseudocoelem (it's ancestors had it but they don't)
- drastic reduction of coelem --> thus, it is more morphologically complex
prominent body section in arthropods
How do arthropods move?
muscles apply force to the exoskeleton
- space for internal organs and circulation of fluids
- in larva, it is also the hydrostatic skeleton
The mollusc body plan (3)
- the foot = large muscle used for mvt on bottom of animal
- visceral mass = region with main internal organs and external gill
- mantle = tissue layer that covers visceral mass
- gutter leading to the mouth (burrow)
- secrete mucus to capture pieces detritus
Did the ability to live in terrestrial environments develop independently in arthropods?
- movement from water to land occurred many times
What adaptations did protostomes make to live on land?
- exchange gases
- avoid drying out
How do worms keep themselves moist?
they live in moist soil
How do arthropods keep themselves moist?
they have a watertight exoskeleton/shell
What is the benefit of moving from water to land?
it opens up new habitats and new types of resources
trait that increases fitness of individuals relative to those without the trait
What are some adaptations for moving?
- presence/absence of limbs
- type of skeleton present
How do worms/caterpillars/maggots move?
manipulate the hydrostatic skeleton
Important adaptations that have allowed protostomes to spread
- insect wing (2/3 of multicellular species are winged)
- waves of muscle contraction to glide among a surface (molluscs)
- jet propulsion (a mantle filled with water, water forced outward through siphon during contraction)
- unfertilized eggs develop into offspring
Important reproductive innovations (2)
- evolution of metamorphosis
- egg that won't dry out on land