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Phylum Nematoda (Body Structures (parasitic adaptations (many) (complex…
Phylum Nematoda
Body Structures
thin, tubular (cylindrical) body
taper at both ends
worm-like
lack segmentation & appendages
longitudinal muscles only
works a/g hydrostatic skeleton
no introvert
thick & multi-layered cuticle
secreted by syncytial epidermis
capable of withstanding high hydrostatic pressure within blastocoel
exhibit eutely or constancy in # of cells
triploblastic
extensive & unsegemented blastocoel
blastocoel acts as N-waste receptacle, circulatory fluid, & hydrostatic skeleton
organs have no mesenteries
float in blastocoel
hydrostatic skeleton
support and movement
longitudinal muscles arranged into 4 quadrants
contractions create s-shaped or whip-like movement
muscle arms connect to nerve cords
parasitic adaptations (many)
complex life cycles w/ different hosts
may manipulate host behavior
penetration or adhesion organs
specialized body surface
high reproductive capacity
reduced sensory and/or digestive organs
Body Systems
blastocoelomate body plan
Digestion & Feeding
complete digestive system
tube-within-a-tube design
mouth at terminal anterior end
anus is subterminal (before tip) at posterior end
alimentary canal
w/ muscular pharynx
linear & unsegmented
no mechanism to move food through
must ingest more food
Circulation & Respiration
lack an actual circulatory system
use fluid in blastocoel
transport gases and nutrients
organs bathed in fluid
cells exchange materials w/ fluid
body contractions mix around fluid
gas exchange (mixture)
diffusion
cells near external surface exchange directly w/ environment
cutaneous
internal cells exchange w/ blastocoel fluid
exchanges w/ environment across cuticle & epidermis
Excretion & Osmoregulation
Nitrogenous waste from cells
collects in blastocoel fluid
empty through 1 excretory pore
near pharynx
have either 1 of 2 different systems to filter fluid
glandular system
Rennette glands
remove N-waste from fluid
tubular system
H-glands & excretory canals
remove N-waste from fluid
Nervous & Sensory
nerve ring & ganglia
surround pharynx
act as a brain
dorsal & ventral longitudinal nerve cords
lateral pair of amphids
anterior end
chemo-sensory
mechano-sensory
Sensory papillae
anterior
posterior
mostly mechano-sensory
Reproduction
Life Cycles
4 larval stages
eggs hatch into 1st larval stage (L1)
L1 develops & molts into L2
L2 develops & molts into L3
L3 develops & molts into L4
L4 develops & molts into adult
1 adult stage
sexually produce fertilized eggs
each separated by molting via ecdysis
sexual only
dioecious
internal fertilization
sexual differences
male
hooked or fanned end
copulatory spicules
hold open female gonopore as sperm is deliverd by penis
posterior end
1 continuous reproductive tube within blastocoel
thinnest end makes sperm
testis
next thickest part is hollow & carries sperm
vas deferens
thickest part stores sperm
seminal vesicle
female
ventral gonopore (genital aperture)
toward anterior
2 continous reproductive tubes within blastocoel
thinnest ends make eggs
ovaries
next thickest part is hollow & carries eggs
oviduct
thickest part stores eggs until fertilization
uteri
2 uteri combine at vagina through which sperm is carried to the eggs
opening through which sperm enters vagina is the gonopore
Taxonomic Divisions
*see tables