the cambrian explosion

multicellularity

many cells and more than one cell type

colonial

many cells and only one cell type

when was the proterozoic eon?

2.5 billion to 540 million years ago

when was the phanerozoic eon?

540 million years ago to present

what was the cambrian period?

appearance of abundant fossils 540 million years ago and diversification of multicellular animal life in the oceans

porifera

tissue absent, asymmetrical (sponges)

placozoa

blob-like aggregations of cells with six cell types, no tissues, engulf food, divide by fission or fragmentation

cnidaria

2 cell layers, no gut or head, O2 via diffusion, decentralized nervous system, asexual reproduction, some sexual reproduction, predatory via stinging. e.g. corals, jellyfish, anemones

bilateria

symmetrical bilaterally with a gut for flow-through feeding/digestion and development of head for sensory and mechanical functions

protostome

forms mouth first during development

deuterostome

forms anus first during development

lophotrochozoa

protostome development with spiral cleavage

molluscs

diverse group, can be sedentary or mobile, often shelled but can secondarily lose shell, capable of complex cognition

cephalopods

includes octopus and squid, largest brain size for body of an invertebrate, known for tool use

platyhelminths

flat worms, free living or parasitic, no body cavity, digestive cavity with mouth and anus

annelids

segmented worms, found in marine and freshwater environments, have a collagen cuticle

ecdysozoa

group characterized by molting

anthropods

have a chitinous exoskeleton, segmented bodies, and paired appendages. e.g. spiders, lobsters

nematodes and nematomorphs

bacteriavores, act as micro predators. e.g. pinworm, whipworm

tardigrades

'water bears', segmented, found in marine, freshwater, and moss environments, highly resistant

echinoderms

marine invertebrates with a mesodermal skeleton, no central nervous system, capable of regeneration. deuterostomes. e.g. starfish

hemichordates

invertebrates with some shared characters with chordates, such as gill slits and a dorsal nerve chord. deuterostomes. e.g. acorn worm

chordates

characterized by notochord, dorsal nerve chord, pharyngeal slits, and post-anal tail. anything with a spine. deuterostomes.

tunicates

marine filter feeders known as sea squirts. deuterostomes.

global temperature changes

earth was cold before the Ediacarian, high glaciation, ended by volcanic activity and CO2 input. drove Cambrian explosion.

global oxygen changes

higher oxygen levels enable multicellular animal function and support larger sizes

why did evolution of vision drive the Cambrian explosion?

by enabling predation

hox genes

genes that provide positional information during development, orchestrating the transition from single cell to complex organism