Week 6: Arthropods

3 main arthropod characteristics

segmented body, jointed appendages, exoskeleton

open circulatory system

system in which blood is not always contained within a network of blood vessels, contains hemolymph

hemolymph

mix of blood and interstitial fluid

hemocoel

body cavity that hemolymph flows through

tagmata

segments arranges in a row and fused together

pros of exoskeleton

protection from predators, prevent desiccation

cons of exoskeleton

limits size (heavy), vulnerable after molting

Ecdysis

periodic shedding of the cuticle in arthropods or the outer skin in reptiles

Clade Chelicerata

includes Merostomata and Arachnida, characterized by chelicerae

chelicerae

paired mouth parts (pincers or fangs)

Clade Merostomata example organism

horseshoe crabs

Clade Merostomata respiration

book gills

Merostomata: carapace

protection, covers the cephalothorax

Merostomata: opisthosoma

protection of abdomen

Merostomata: chelicera

manipulate food, first pair of appendages

Merostomata: gill opercula

protects gills (hard covering)

Merostomata: telson

assist with flipping over, anchoring

Merostomata: compound eyes

photoreception

Merostomata: simple eyes (ocelli)

UV/visual light detection

Merostomata: pedipalps

assist in movement, 2nd set of clawed appendages

Clade Arachnida example organism

SPIDER, scorpion, ticks, mites

Clade Arachnida respiration

book lungs

spider: cephalothorax

the anterior tagma where legs attach

spider: abdomen

possess reproductive, digestive, respiratory and web spinning functions

spider: chelicera/fangs

manipulate food, inject venom

spider: spinnerets

spin silk (on abdomen)

spider: pedipalps

handle food

Clade Myriapoda

includes clades Diplopoda and Chilopoda

Clade Diplopoda

millipedes, 2 pairs of legs per segment (diplo = 2)

Clade Chilopoda

centipedes (one pair of legs per body segment) (think C and C)

Clade Crustacea --> Malacostraca --> Decapoda

contains crayfish, use gills for respiration

crayfish: rostrum

protects stalked eyes and cerebral ganglia

crayfish: antennae

longer sensory organs

crayfish: antennules

shorter sensory organs

crayfish: compound eyes

under rostrum, vision

crayfish: carapace

covers/protects cephalothorax

crayfish: swimmerets

for females, holds and aerates fertilized eggs

crayfish: copulatory swimmerets (male)

modified swimmeret for sperm transfer

crayfish: seminal receptacle (female)

receive sperm

crayfish: telson

central tail fin, propulsion

crayfish: uropods

lateral portions of tail, propulsion

crayfish: chelipeds

catch prey, defense

crayfish: walking legs

biramous, locomotion

crayfish: gastric muscles

attach from stomach to carapace, help move food

crayfish: cardiac stomach

food storage

crayfish: pyloric stomach

chemical breakdown of food

crayfish: gills

gas exchange

crayfish: intestine

chemical digestion

crayfish: green glands

osmoregulation

crayfish: digestive glands

secrete digestive enzymes into intestine

Clade Hexapoda

six-legged arthropods, includes Clade Insecta

Clade Hexapoda respiration

tracheal system (trachea and spiracles)

insect land adaptations

exoskeleton, walking appendages, internal fertilization, cuticle, specialized respiratory, excretory and digestive structures, wing

hemimetabolous life cycle

incomplete metamorphosis, nymphs look like adults

holometabolous life cycle

complete metamorphosis, egg to larva to pupa to adult

Clade Coleoptera

beetles, holometabolous

Clade Diptera

flies, mosquitos, holometabolous

Clade Hymenoptera

wasps, ants, bees, holometabolous

Clade Lepidoptera

butterflies, moths, holometabolous

Clade Hemiptera

true bugs, hemimetabolous

Clade Orthroptera

grasshopper, crickets, hemimetabolous

grasshopper: compound eyes

produce image, sight in all directions

grasshopper: antennae

sensory organs

grasshopper: spiracles

regulates gas exchange, prevents water loss

grasshopper: forewings

flight, protect hindwings

grasshopper: hindwings

flight

grasshopper: ovipositor

lay eggs (female only)

grasshopper: tympanum

detect sound

grasshopper: mandible

mastication

grasshopper: maxilla

food manipulation

grasshopper: labrum

top lip

grasshopper: labium

bottom lip

grasshopper: gastric ceca

secrete digestive enzymes (2 in pic)

grasshopper: testes

produce sperm

grasshopper: ovaries

store eggs

grasshopper: crop

food storage and digestion (1 in pic)

grasshopper: malpighian tubules

excretory, used to eliminate waste, osmoregulation (3)