Intro to Ecdysozoa Lecture 13 Flashcards
support structure in Ecdysozoans
Exoskeleton
why is exoskeleton important
- barrier to desiccation
protection
shape of animal
frame for muscle attachment
features of Ecdysozoa
periodic molting (Ecdysis)
three layered cuticle
lack cilia for locomotion
amoebid sperm
Cycloneuralia (5) within Ecdysozoans
Priapulida Kinorhyncha Loricifera Nematomorpha Nematoda (named for position of brain around the pharynx)
Molting (Ecdysis)
periodic replacement of exoskeleton (believed to have only evolved once)
cuticle layers (3)
epicuticle (outside)- thin protein
exocuticle- protein, calcium, chitin
endocuticle (inside)- thick calcium, thick membranous layer
(secreted by epidermis)
Process of Ecdysis (3 steps)
- epidermis undergoes round of cell division and separates from exoskeleton (apolysis)
- new exoskeleton is secreted by epidermis, remains soft until old cuticle is shed
- new cuticle expands and hardens
Cycloneuralia also known as Introverta
spiny retractable proboscis (introvert) present in all phyla
Nematoida
Nematoda and Nematomorpha
traits of Nematoida
cuticle made of collagen
reduction of circular muscles
epidermal longitudinal nerve cords
amoebid sperm (tailless)
Nematodes
ecto and endoparasites of crops, animals and humans
impermeable cuticles good for parasitic nematodes
most common nematode parasite?
Pinworm
Cryptobiosis
Suspension of life processes in situations of unfavorable conditions into resistant states (nematodes, rotifers and tardigrades)
The model Nematode?
C. elegans
- soils, in temperate regions
- first multi-celled animal to have its genome completely sequenced
Nematode bauplan
adult nematodes have 1,000 somatic cells
tube within a tube (mouth at anterior extends back to the anus)
lack circulatory or respiratory systems
free-living vs parasitic forms
4 molts of the cuticle during growth
complicated lifestyle, usually with several different hosts
Human diseases caused by Nematodes
Elephantiasis (filarial nematodes)
African river blindness
Hook worms and Whip worms
One host parasites
Intestinal roundworm
Hook worm
Whipworm
Two host parasites
Blood-sucking insect acts as intermediate host
Heartworm
Guinea worm
How to get rid of parasites?
Finding out the specifics of the different molting processes in the parasitic nematodes and disrupting some stage of molting
molting in nematodes
Relatively little is known about molting in nematodes, but making comparisons to molting in Arthropods may uncover aspects that constrain molting
Difficulties in Nematodes and Arthropods
hard to connect similar underlying control of molting in both
Nematodes lack key enzymes (sterols)
cuticle is collagen rather than chitin
enzymatic cascade that mediates release of exoskeleton in nematodes may be distinct from arthropods
Altering molting
Determine what genes are responsible for molting and inactivate them, killing the parasite and not affecting the host (RNA interference)
Regulation of molting in Nematodes and Arthropods
Master regulators of molting may function in similar systems between the two
regulation of molting is conserved in Arthropods
(supports hyp that molting only evolved once)
Nematomorpha
horsetail worms very long and slender terrestrial and fw single pseudocoelom lack of circular muscles Semi-parasitic (Larvae parasitic in insects, adults free-living in fw)
Scalidophora or Cephalorhyncha
Kinorhyncha
Priapulida
Loricifera
Priapulida
- bottom dwelling, predatory worm
large spiny eversible head end (introvert)
distinctive plumose caudal appendage in some
few species, but common in Cambrian Sea and fossils well known
Large pseudocoelom
Loricifera
recently discovered
occupy interstitial marine shell gravel, and deeper sediments (annoxic environments)
very tiny
Bauplan of Loricifera
Head region Trunk region (6 plates that compose lorica) Neck region (between head and trunk) withdraw head into neck and both into trunk
Scalids
spine on the head region that stick out protectively when head is extended and face outwards when head is withdrawn
Kinorhyncha
sediment dwellers in global oceans
head, neck and trunk
Trunk has 11 segments called (zonites) with a single dorsal plate (tergite) and two ventral plates (sternites)
head retracted into trunk (introvert)
mouth surrounded by spines called stylets