The document summarizes key arthropod groups - trilobites, crustaceans, chelicerates, and uniramians. Trilobites had segmented bodies and paired appendages. Crustaceans are diverse but generally have a hard exoskeleton, antennae, gills, and legs attached to gills. Chelicerates include spiders and have a cephalothorax, four pairs of walking legs, and specialized appendages like chelicerae. Uniramians include insects, centipedes, and millipedes, and have adaptations like wings, tracheal respiration, and specialized mouthparts and societies.

1. Trilobite
Subphylum Trilobita (trilobites)
Example members: trilobites (now extinct)
Key features:
-body composed of many segments
-each segment had 2 appendages (each appendage
was divided into 2 branches – a walking leg and a
feather-like gill)
Subphylum Crustacea (crustaceans)
Example members: crabs, shrimp, lobster, water fleas, barnacles, pill bugs, crayfish
Key features:
-35 000+ members
-members are primarily aquatic
-members vary in form and size
-3 body segments (head, thorax, and abdomen)  sometimes head
and thorax are fused into a cephalothorax
-hard exoskeleton (aka carapace) reinforced with calcium carbonate
(CaCO3) (aka limestone)
-2 pairs of antennae (“feelers”) and mandibles
-gas exchange with gills
-each walking leg is attached to a gill (like in trilobites)
-swimmerets – flipper-like appendages for swimming
Crustaceans have appendages that vary greatly. For example, crayfish have claws, walking legs,
swimmerets and uropods, as well as modified mouth parts.

2. Subphylum Chelicerata (chelicerates) Tick
Example members: spiders, scorpions, ticks, mites, horseshoe crabs
2 classes
1) Class Arachnida (arachnids such as spiders, scorpions, ticks, mites)
2) Class Merostomata (horseshoe crabs). A very ancient class (“living fossils”). Not really crabs, of
course.
Key features:
-body divided into 2 segments (a cephalothorax (head fused with a thorax) and an abdomen)
-4 pairs of walking legs on cephalothorax
-most are carnivores
-have air tubes and book lungs
-sensory bristles covering body instead of antennae
Unique to chelicerates are 2 pairs of appendages attached near mouth:
1) Chelicerae – spiders use these appendages to bite and paralyze prey
Spiders inject enzymes that liquefy the prey and they suck the “juice” out!!
2) Pedipalps – 1 pair of appendages usually used for handling prey
In scorpions, modified into huge claws
All spiders can produce silk (a tough protein that is 5x stronger than steel!). Some spiders spin webs
using spinnerets.
Ticks and mites are usually parasites. Ticks can carry diseases,
such as Lyme disease, which can cause joint inflammation, and
heart rhythm and neurological problems.

3. Subphylum Uniramia (uniramians)
Example members: millipedes, centipedes, insects
‘Uni’ – one, ‘ramus’ = branch
All uniramians have 1 pair of antennae and appendages that do not branch.
There are (at least) 3x more species of uniramians than all other groups of animals!
Centipede
3 classes
1) Class Chilopoda (centipedes)
-Predatory  carnivorous
-Head has 1 pair of antennae and a chewing mouth
-1st body segment has a pair of poisonous claws
-2 groups of simple eyes
-1 pair of legs per segment
2) Class Diplopoda (millipedes)
-Detritus feeders  scavengers
-Head has 1 pair of antennae and a chewing mouth
Millipede
-2 pairs of legs per body segment
3) Class Insecta (insects, such as bees, moths, grasshoppers, etc.)
-900 000+ species
-3 part segmented body: head, thorax, abdomen
-3 pairs of legs attached to thorax
-1 pair of antennae and 1 pair of compound eyes
-Often have 2 pairs of wings on the thorax
-Tracheal tubes for respiration
Anatomy of a wasp

4. Grasshopper mouthparts
Insect Adaptations
Feeding :
-3 pairs of appendages used as mouthparts including mandibles (cutting jaws)
-may secrete digestive enzymes or other chemicals
ex. mosquitoes – anticoagulants prevent blood clotting
bees – change nectar to honey
Movement :
-Legs have spines and hooks for defense
-Legs used for jumping, holding prey (ex. praying mantis)
-Unassisted flight with wings (variety of speeds and maneuverability)
Insect societies:
Society: collections of individuals of the same species
that live together
Individuals depend on one another (ex. ants, bees,
termites)
Division of labour: members of different castes (types
of individuals) have a body that is specialized for its
function (ex. reproductive females, reproductive males,
workers)
Termite castes
Communication:
-Use sound, visual, chemical signals for mating (ex. cricket chirp, firefly light)
Pheromones: convey info of food through a “waggle dance” (see p. 627)
Waggle dance

5. Compound eyes
Intriguing Structures in Class Insecta
Compound Eye
Many arthropods have compound eyes.
Compound eyes are made up of repeating units, the
ommatidia, each of which functions as a separate visual
receptor.
‘Microscope A’ shows a slide of a compound eye.
Spiracles
Insects and some more advanced spiders have
spiracles on their exoskeletons to allow air to
enter the trachea.
In insects, the tracheal tubes deliver oxygen
directly into the animals' tissues.
The spiracles can be opened and closed in an
efficient manner to reduce water loss.
‘Microscope B’ shows a slide of an insect
spiracle.
Honeybee mouthparts
Mouthparts
Many insects have mouthparts adapted for
feeding. Honeybees have a number of
adaptations for gathering, processing, and
storing food.
In honeybees, the mandibles are very small and
suitable for moulding wax. The labium is curved
downwards and inwards forming a tube used
for sucking up nectar.
‘Microscope C’ shows a slide of honeybee
mouthparts.