bio 205 chapter 14: the arthropods part 1

phylum arthropoda

largest phylum in kingdom animalia
75% of all animal species
1.5-3 million species
jointed body → indication of segmentation
unequal segmentation
believed to have evolved from a group of annelid worms
bilaterally symmetrical
triploblastic coelomates
protostomes
complete digestive tract (gut)

crustacean body regions

cephalothorax and abdomen

cephalothorax

the head and thorax are fused, antennae and legs extend off

abdomen (crustacean)

swimming appendages extend off

insect body regions

head, thorax and abdomen

head

antennae extend off

thorax

legs and possibly wings extend off

abdomen (insect)

sits posterior to the thorax and does not possess appendages

antennae

chemosensory and/or photoreceptive

walking legs (pereopods)

for motility, leg number varies amongst the arthropods

pleopods (swimmerets)

in most aquatic arthropods, keep the abdomen elevated

wings

for flight, either one or two pairs, only in select insect species

mandible

jaws

chelicerae

feeding appendages outside of the mouth

exoskeleton

an acellular “armor-like” body covering that is comprised of chitin and protein

sclerotization of protein

results in the hardening of an exoskeleton, hardened with minerals in terrestrial species and calcium carbonate in aquatic species

ecdysis (molting)

the removal of the exoskeleton to allow for body growth and is hormonally controlled

apodemes

internal folds of the exoskeleton where muscles attach, allows for the exoskeleton to cover separate body regions and appendages while keeping the arthropod jointed

epicuticle

thin outermost protein layer, covered by a layer of wax which is water resistant or helps retain water, may contain pigments

procuticle

consists of an outer exocuticle and an inner endocuticle

exocuticle

an interwoven network of chitin and protein, hardened through biomineralization

endocuticle

an interwoven network of chitin and protein, more flexible than the exocuticle

simple columnar cells

comprise the bulk of the epidermis and are responsible for secreting the molting fluid consisting of chitinases and proteinases

gland cells

secrete wax for the epicuticle

trichogen cells

setae (chaetae) forming cells

tormogen cells

sensory socket-like cells surrounding the base of a trichogen cell

ecdysone

hormone that triggers ecdysis (molting)
secreted by the Y-organ in the head of crustaceans and the prothoracic glands in the thorax of insects, and causes simple columnar cells to secrete molting fluid

Y-organ

in the heads of crustaceans and prothoracic glands in the thorax of insects, secretes ecdysone to trigger ecdysis (molting) to begin

X-organ

in the eyestalks and secrete another hormone to turn off the secretion of ecdysone by the Y-organ or prothoracic glands

instar (intermolt)

the period of time between molts and the arthropod is most active during this time

proecdysis

1) ecdysone triggers the simple columnar cells to begin secreting molting fluid
2) molting fluid begins to degrade old endocuticle
3) new epicuticle starts to form when gland cells begin secreting wax and protein - repels molting fluid so it is not digested

true ecdysis

1) molting fluid continues to degrade old endocuticule and begins to degrade old exocuticle
2) new exocuticle begins to form
3) old exoskeleton cracks at ecdysial lines
4) soft bodied arthropod exist old exoskeleton

ecdysial lines

weaker portions of the exoskeleton

postecdysis

1) new exocuticle continues to form
2) new endocuticle begins to form
3) arthropods is able to resume normal activity

arthropod nervous system

cephalic (cerebral) ganglia, ventral nerve cord, segmental ganglia

cephalic (cerebral) ganglia

comprise the brain

ventral nerve cord

extends posteriorly from the brain

segmental ganglia

found along the ventral nerve cord

crustacean brain regions

protocerebrum, deutocerebrum, tritocerebrum

protocerebrum

the anterior portion, possesses optic nerve that run to the eyes

deutocerebrum

the middle portion, possesses nerves that run to the first pair of antennae

tritocerebrum

the posterior portion, possesses nerves that run to the second pair of antennae and has a hole in it that allows for the esophagus to pass through it

chelicerate and uniramian brain regions

protocerebrum and tritocrerburm

compound eyes

consists of multiple lenses allowing for a highly peripheral vision

arthropod circulatory system

open circulatory system consisting of a hemocoel, (sometimes) multiple hearts, and 2 ostia in the heart

hemocoel

the cavity in which vessel empty blood into

ostia

holes in the heart through which blood can enter the heart and re-enter the circulation

arthropod digestive system regions

foregut, midgut and hindgut

foregut

for the intake and storage of food

midgut

for the mechanical and chemical digestion of food and for the absorption of nutrients

hindgut

for the reabsorption of water and for fecal formation

foregut structures

mouth, pharynx, esophagus, crop

mouth

for ingestion of food

pharynx

a temporary storage chamber for ingested food

esophagus

a muscular organ that carries food from the pharynx to the crop

crop

the primary storage chamber for food

midgut region structures

proventriculus, digestive (gastric) ceca, midgut organ

proventriculus

a muscular valve that moves food from the crop to the midgut

digestive (gastric) ceca

produces and secretes enzymes into the midgut to break down the food

midgut organ

the organ in which digestion occurs followed by nutrient absorption

hindgut structures

malpighian tubules, intestine, rectum, anus

malpighian tubules

excretory tubules off of the intestine that remove liquid and gaseous waste from the blood and places it into the intestine

intestine

allows for the reabsorption of water

rectum

forms solid fecal matter

anus

allows for the release of fecal matter and waste collected by the malpighian tubules

testes

produce sperm through meiosis

vas deferens

carry sperm from testes to seminal vesicles

seminal vesicles

store organisms own sperm

ejaculatory ducts

carry sperm from seminal vesicles to aedeagus (penis) during mating

aedeagus (penis)

inserted into the vagina of a female to deliver sperm

accessory glands

produce lubricating fluid (semen)

ovaries

produce eggs through meiosis

lateral oviducts

run from each ovary to common oviduct

seminal receptacle (spermatheca)

stores collected sperm

vagina

where aedeagus (penis) is inserted and eggs are released

accessory glands

produce advesive substance for egg deposition or keeping groups of eggs together

gradual metamorphosis

paurometabolous development, the juvenile resembles the adult but is smaller in size
egg → nymph → adult
performed by true bugs and grasshoppers

complete metamorphosis

holometabolous development, a complete change occurs in the development
egg → larva → pupa → adult
the larva looks nothing like the adult and does not compete with the adult
must be genetically complex having genes for the larval stage and for the adult
performed by beetles, butterflies and moths

pupation

the change from larva to an adult

queens

the only fertile female capable of producing eggs that possesses a growly enlarged ovary, present in termite and honeybee colonies

worker termites

sterile females that feed the developing offspring

soldiers

sterile female termites that protect the colony with their enlarged mandibles

male termites

winged fertile males responsible for fertilizing the queen’s eggs, possibly fertilize the eggs of other populations

worker honeybees

sterile females that feed the developing offspring, collect the nectar to produce honey and protect the time, and these are the bees with stingers

female bees

produced through sexual reproduction and are diploid

male bees

produced through parthenogenesis and are haploid