Arthropoda

Why are arthropods so speciose?

• Small, which allows populations to easily separate into different niches and undergo speciation

• Highly mobile

• Have invaded all habitats; marine, freshwater, terrestrial

• Short generation times and lots of offspring; higher likelihood of variation and speciation

• Innovative adaptions; exoskeletons, sensory systems, etc.

What clades are arthropods members of?

• Protostomes

• Coelomates

• Ecdysozoa; under go ecdysis and shed their cuticle (exoskeleton)

What are the advantages and disadvantages of an exoskeleton?

Advantages:

• Extremely protective

• Allowed for the invasion of land because it prevented them from drying out

Disadvantages:

• Exposed and vulnerable after molting

• Energy intensive to build a new exoskeleton

What are the 5 monophyletic groups of arthropods?

• Trilobites

• Myriapods

• Chelicerates

• Crustaceans

• Insects

What are the 5 arthropoda subphyla?

• Trilobitomorpha

• Chelicerata

• Myriapoda

• Crustacea

• Hexapoda

What are the differing characteristics among arthropods?

Crustaceans:

• 2 pairs of antennae

• 5 or more pairs of legs

Insects:

• 3 pairs of legs

• 1 or 2 pairs of wings

Arachnids:

• No antennae

• 4 pairs of legs

Myriapods:

• 1 or 2 pairs of legs per body segment

Describe the general arthropod morphology.

• Body segmentation with distinct head, thorax, abdomen

• Jointed appendages

• Open circulatory system

• Malpighian tubes: Kidney like structures that help with osmoregulation

• Gonochoristic with ovaries or testes

• Brain and nerve ganglia throughout the body

How do arthropods generally reproduce?

• Internal fertilization (including aquatic)

• Some can exhibit parthenogenesis

Describe general arthropod respiratory system.

• Spiracles: Openings on the exoskeleton where air passes through

  • Ductwork of tubes distribute oxygen throughout the body (trachea and tracheoles)

• Book Lung: Firm gill-like organ that absorbs oxygen present in arachnids

• Gills: Present in crustaceans

What is the class of subphylum Trilobitomorpha?

Trilobita

Describe class Trilobita.

• Extinct

• Over 20,000 species described in fossil record

• Highly successful group of arthropods

Describe trilobite morphology.

• Resource partitioning between species on different parts of the shore

• Predators and detritivores of the intertidal zone

What is the defining characteristic of chelicerates?

Chelicerae, which are fangs/special mouthparts

What are the 3 classes of subphylum Chelicerata?

• Arachnida

• Merostomata (horseshoe crabs)

• Pycnogonida (sea spiders)

What are the 3 orders of class Arachnida?

• Aranea (spiders)

• Scorpiones (scorpions)

• Acari (mites and ticks)

Describe the morphology of spiders.

• Cephalothorax; fused head and thorax

• Chelicerae with hollow fangs that inject venom

• Usually 8 compound eyes (number can differ)

• Spinnerets on the end of the abdomen produce silk strands

Describe spider web-making.

• Silk is made of proteins that interact with moisture in the air to become sticky

• A spider can have up to 7 different kinds of silk with different properties

• Spiderweb shape is characteristic of spider type (orb, funnel, etc.)

• Not all spiders build webs for hunting; some set traps on the ground or are ambush hunters

How do spiders reproduce?

• Gonochoristic with internal fertilization

• Males are usually much smaller, and females eat the male after mating

• The male fertilizes the eggs while being eaten, and his body nourishes the growing eggs

• Females carry the egg sac made of silk until the eggs hatch

Describe scorpion morphology.

• Pedipalps (pincers)

• Stinger that injects venom

Why are horseshoe crabs special in the medical industry?

Their blood contains amoebocytes for defense against pathogens, which are used by humans to make Limulus amoebocyte lysate (LAL), which can detect bacterial contamination

Why do horseshoe crabs have blue blood?

They use hemocyanin with copper to transport oxygen instead of hemoglobin with iron

What are the 4 classes of subphylum Myriapoda?

• Chilopoda (centipedes)

• Diplopoda (millipedes)

• Pauropoda (sometimes an order of diplopoda)

• Symphyla (sometimes an order of chilopoda)

Describe the morphology of centipedes.

• One pair of legs per body segment

• Ocellie

• Fangs and venom glands

• Tergites: Chitinous plates along the body that define the body segments and make up the exoskeleton

• Gonopods: External genitalia where sperm is delivered during internal fertilization

Describe the morphology of millipedes.

• Two pairs of legs per body segment

• Ocelli

• Tergites

• Gonopods

Describe the ecology of centipedes and millipedes.

Centipedes

• Venemous predators

Millipedes

• Non-venomous decomposers

What are the 4 classes of subphylum Crustacea?

• Branchiopoda (water fleas, brine shrimp)

• Maxillopoda (copepods, barnacles)

• Ostracoda (seed shrimp)

• Malacostraca

What is the common characteristic of class Branchiopoda?

Branchiopod: A feathery, gill-like appendage used for swimming, grasping, and respiration

How do barnacles eat?

They use feathery feeding appendages to catch floating particles (suspended filter feeding)

Who are the members of malacostraca?

Crayfish, shrimp, krill, prawns, mantis shrimp, sand hoppers, crabs, lobsters, isopods, amphipods (scuds)

Describe general crustacean morphology.

• Cephalothorax

• Pereiopods

  • Chelipeds (pincers or claws) and 4 pairs of legs; 5 pairs of walking legs total

• Pleopods

  • Swimmerets along the abdomen

  • Upper pair in males are gonopods for copulation

• Gills

• 2 pairs of antennae

• Multiple complex mouthparts

• Excretory organs near the mouth for osmoregulation

• Complete digestive tract

How do crustaceans reproduce?

• Majority: Gonochoristic with internal fertilization

  • Female carries the fertilized eggs against her pleopods

  • Life cycle can be complex with planktonic larval stages (ie. nauplius larvae)

• Cladocerans: Parthenogenesis

  • Diapause stage: dormant egg waiting to hatch

• Barnacles: Hermaphrodites

  • Long external genitalia deliver sperm to their neighbors

Describe crustacean ecology.

• Carnivores, herbivores, detritivores, filter feeders, parasites

• Freshwater, terrestrial, marine

• Can be part of zooplankton community

What are the two classes of subphylum Hexapoda?

• Entognatha (wingless hexapods)

• Insecta (winged hexapods)

What is an order of class Entognatha?

Collembola (springtails)

Describe the morphology of springtails.

• Cone around the mouthparts, unlike insects who have their mouthparts exposed

• Wingless and common in soil

• Not true insects

How speciose are insects?

Number of known species estimated to be 1.1 million, which is half of all organisms described

Why are insects important?

• Major economical and medical roles for humans

• Critical ecological roles in nature, such as pollination

What are the 10 orders of class Insecta?

• Ephemeroptera (mayflies)

• Odonata (dragonflies and damselflies)

• Orthoptera (grasshoppers, katydids, crickets)

• Plecoptera (stoneflies)

• Hemiptera (true bugs; stinkbugs, cicadas, aphids)

• Coleoptera (beetles)

• Diptera (flies)

• Trichoptera (caddisflies)

• Lepidoptera (butterflies and moths)

• Hymenoptera (ants, bees, wasps)

What are the 5 aquatic orders of Insecta?

• Ephemeroptera (mayflies)

  • 2-3 long cerci

  • 2 pairs of upright wings

  • Forewings longer than hindwings

• Odonata (dragonflies and damselflies)

  • 2 pairs of wings that lay perpendicular (dragon) or parallel (damsel) to body

  • Hindwings larger than forewings (dragon) or wings of equal size (damsel)

• Plecoptera (stoneflies)

  • 2 short cerci

  • 2 pairs of flat wings

  • Hindwings larger than forewings

• Diptera (flies)

  • No cerci

  • 1 pair of wings

  • Sucking mouthparts

• Trichoptera (caddisflies)

  • No cerci

  • 2 pairs of tent-like wings

  • Wings covered in tiny hairs

What are the 2 kinds of insect development?

• Holometabolous (diptera, lepidoptera, coleoptera)

  • Egg - larvae - pupa - adult

• Hemimetabolous (orthoptera, odonata)

  • Egg - larvae - adult

Describe general insect morphology.

• Segmented body with head, thorax, abdomen

• Jointed appendages

• Chitinous exoskeleton

• Undergo ecdysis as they grow

• Compound eyes; multiple lenses in the eye allowing them to see multiple images at once

• Antennae allowing them to sense chemicals, sound, taste, touch, and vibration

• Wings (1 or 2 pairs)

• Capability of producing and delivering venom (sometimes)

What is thought to be the origin of insect wings?

Option 1:

• Outcroppings of the exoskeleton for thermoregulation

Option 2:

• Gill where oxygen was absorbed for respiration

Both options:

• Muscles developed around the wing allowing it to be functional for flight

How do insects reproduce?

• Gonochoristic with internal fertilization

• Complex/elaborate genitalia to prevent different species from mating

• Egg depositing onto plants, soil, or water

  • Many lepidopterans need to lay eggs on a specific host plant for the larvae to survive

• Parasitoids: Lay their eggs in/on a host species using an ovipositor, and the larvae consume the host after hatching

Describe insect ecology.

• Found mainly in terrestrial areas, also in freshwater, brackish water, and salt marshes

• Abundant in soil, forest canopies, and can also be found in deserts and wastelands

• Most animals have insects as endo or ectoparasites