Complex Animals: Annelids & Arthropods - CrashCourse Biology #23
chitin
A structural polysaccharide, consisting of amino sugar monomers, found in many fungal cell walls and in the exoskeletons of all arthropods.
Class Polychaeta
Almost all of these are marine species, and they're really diverse, but the ones you've probably seen evidence of are the lugworms, the ones that dig holes at the beach and leave piles of castings on the sand. ex. bristle worms.
chaetae
Bristle-like extensions found in some annelids.
Subphyla Chelicerata
Greek for "arm-lips," which refer to their long fang-like pincers. they have simple eyes with just one lens and lack antenna. Includes spiders and scorpions, horseshoe crabs, ticks, and mites
class oligochaeta
Name refers to the synapomorphy "chaetae", or bristles, but only an "oligo", few of them. They eat soil and crap it out the other end, allowing air and water to circulate in soil. ex Earthworms
phylum Crustacea
The animal group that includes mostly aquatic animals such as crabs, lobsters, crayfish, and shrimp., two body parts; two pairs of antennae on the head; aquatic
Phylum Annelida
They are segmented and have little bristles on their bodies called chaetae that provide traction and help them move through the dirt. ex segmented worms, earthworms, leeches
phylum arthropoda
They have segmented bodies that, in most cases, are broken up into three segments: head, thorax and abdomen. They have an exoskeleton, paired and jointed appendages. ex. insects
Class Arachnida
They have what's called a cephalothorax, which is a head segment and a thorax segment fused together, with eight legs and an abdomen behind. Most arachnids are carnivorous or parasitic and they're very skittery. Includes spiders, scorpions, ticks, mites
metamorphosis
a transformation or dramatic change
80% of known animal species are
arthropods
Meganeura
giant dragonflies from the Carboniferous period (approximately 300 million years ago)
Segmentation
is the repetition of anatomically identical units that can be added to and modified to serve different purposes as animals evolve
class Hirudinea
leeches, a lot of which are parasitic . Their powerful suckers they've got them on both ends of their body, the posterior one being used to anchor itself while the anterior one that surrounds its mouth attaches to its host. All leech species are carnivorous and they are hermaphrodites like earthworms.
synapomorphy
traits that set one group of animals apart from its ancestors and from other groups that came from the same ancestors
Plesiomorphy
very basic traits that are shared by animals with a common ancestry
Phylum Myriapoda
"many feet" Terrestrial and have antennae and jaw-like mandibles. ex. the millipedes and centipedes
phylum Hexapoda
"six feet" three-part bodies, consisting of a head, a thorax, and an abdomen, three pairs of jointed legs that come off the thorax, compound eyes, and two antennae
centipede
(literally, "hundred-legged" creature); wormlike animal with one pair of legs on most of its segments; carnivores and have poisoned claws to paralyze their prey; generally have between 20 and about 350 legs; don't cuddle
millipede
(literally, "thousand-legged" creature); wormlike animal with two pairs of legs on most of its segments; vegetarians; actually got anywhere between 94 and 394 legs
Carboniferous period
354 to 290 mya. refers to the rich coal deposits found in rocks of this age. Cooler period, much of the land covered by forest swamps. Very large plants and trees became prevalent. Terrifyingly big insects.
