### animal | arthropod | tardigrade:

Terrestrial tardigrade
* become active only when surrounded and rehydrated by water.
* require a film of water around the body to conduct an active life.

Terrestrial arthropod
* Most terrestrial arthropods have structures.
* Some terrestrial arthropods excrete waste
  - have tubules
  - possess tracheae
* have an excretory system that conserves water and eliminates waste
  - internal surfaces that are specialized for gas exchange, via air sacs

### animal | arthropod:

Trilobite
* Most trilobites are small, the average size being perhaps about two or three inches
  - burrow into sediments
* Most trilobites have backs
  - characteristics
  - other characteristics
  - spines
* Most trilobites share certain features
  - unique features
* Some trilobites belong to extinct phyla
  - develop eyes
  - eat organisms
* Some trilobites have antennas
  - attributes
  - compound eyes
  - heads
  - projectiles
  - sex
  - live during periods
* Some trilobites live in environments
  - shallow water
  - survive fossilization
  - thrive in environments.
  * Underneath and rarely preserved are three pairs of legs for the head and paired legs for each pleural groove. Trilobites are the earliest known animal to have vision. Some possessed eyes and some seem to have no eyes at all, while others had eyes made up of many parts that could see all around the animal. Trilobites ranged in length from to , with a typical size range of. The world's largest trilobite, 'Isotelus rex', was found in 1998 by Canadian scientists on the shores of Hudson Bay
* appear to be the first form of life to have complex eyes.
* are Arthropods
  - a well-known fossil group of extinct marine arthropods that form the classTrilobita
  - an important group of extinct marine arthropods characterized by a segmented body
  - arthropods that no longer live anywhere on earth
  - arthropods, in the same alliance as modern insects
  - available in different materials, sizes, and time periods
  - by far the most abundant of all skeletonized Cambrian metazoans
  - common, but different fossil assemblages are found in successively younger rocks
  - comparatively rare after the Devonian
* are extinct arthropods known only in fossil form
  - marine animals which lived gazillions of years ago
  - famous for their eyes
  - found as fossils throughout the world
* are important guide fossils because their morphology changed frequently
  - in the stratigraphic subdivision of the period
  - kind of like a big version of roly-polys
  - long extinct but jellyfish still swarm the oceans
  - much larger than the ostracodes
  - one of the most successful animals to live on Earth
  - perhaps the most distinctive Palaeozoic fossil
  - quite popular among fossil collectors and enthusiasts
  - rare, represented only by the proetids
  - small marine creatures that are now extinct
  - the earliest arthropods and are the first known fossils with eyes
  - possess vision
  - first, most frequently, discovered lifeforms on Earth
  - useful in determining the relative age of some sedimentary rocks
* become increasingly rare.
* first appear in rocks of lower Cambrian age.
* have a segmented body that is divided by into three vertical lobes
  - an older history than the famous dinos, and tell a greater picture of their times
  - two pleural lobes and an axial lobe in the center
* include predators.
* includes brains
  - carapaces
  - cell membranes
  - cells
  - corpi
  - cytoplasm
  - faces
  - nuclei
  - plasma membranes
  - sections
  - shells
  - skulls
  - thoraxes
  - vacuoles
* is an arthropod
* make their entrance onto the earth's stage during the late Cambrian Period
  - up one of the most fascinating and diverse groups in the fossil record
* possess eyes.
* rank among the most important of early animals.
* scavenge the ocean bottom for worms and other food.
* shed their skin as they grew by molting.