Phylum Nematoda

Clade Ecdysozoa

-Animals that molt a
cuticle

-Cuticle is an outer
body covering

-Both coelomate
and pseudocoelomate
phyla represented

-Most constrained
body plans among
metazoa

Phylum Nematoda – the roundworms

-Most constrained body plan – pressurized pseudocoel

-Elastic cuticle contains spacious pseudocoel under pressure

-Only longitudinal muscles present – excel at moving through
tight spaces (interstitial fauna) – “writhe” when removed from
environment

-Largest number of individual metazoans

Phylum Nematoda – Body Plan

-Highly constrained plan

-Must swallow against
hydrostatic pressure (~7 psi)

-Must form shelled eggs
internally – mostly dioecious
with internal fertilization

-No respiratory structures –
limits size and thickness

Nematode parasites

Unlike platyhelminth parasitic worms that absorb food
through their tegument, nematode parasites must
swallow food because their cuticle is a barrier.

Guinea worm – Dracuculus medinensis

Ingest eggs in contaminated water

Phylum Nematoda Germ layers

Triploblastic, but pseudocoelomate

Phylum Nematoda-symmetry

Bilateral

Phylum Nematoda- Skeleton system

Hydrostatic- using pseudocoelom

Phylum Nematoda-Mode of Locomotion

Writhing, longitudinal muscles working
against pseudocoel

Phylum Nematoda-Distinguishing Characteristic(s)

Elastic cuticle, hydrostatic skeleton, only
longitudinal muscles, writhe