functions of different animal coeloms

1
(No Transcript)
2
functions of different animal coeloms

• simple circulatory system
• increase in body size possible (follows from 1)
• storage area for organs, separates organs from
  gut
• independent growth of organs possible (e.g.
  coelomic space allows storage of gametes,
  seasonal reproduction enhanced)
• allows for developmental/physiological
  coordination via circulating hormones
• hydrostatic skeleton - burrowing!
• also allows for eversible mechanisms, such as
  annelid proboscis, and hence diverse feeding
  methods can evolve

3
one recent Metazoan phylogeny (molecular data)
NEMERTEA MOLLUSCA BRACHIOPODA BRYOZOA PHORONIDA
ANNELIDA ECHIURA POGONOPHORA SIPUNCULA CHAETOGNATH
A
PLATYHELMINTHES
from Ruiz-Trillo et al. (1999) Science 283
1919.
4
WHY WORM?
body form adapted to crevices burrowing front
and back specializations sensory information
gathered in head region ("cephalization") coupled
with regeneration, offers potential
reproductive (budding) and survival
advantages high surface area/volume
ratio streamlined movement through
environment (water, etc...)
5
the parchment worm Chaetopterus variopedatus
the sand worm Nereis vexillosa
photo by Erling Svensen www.uwphoto.no
http//www.lanecc.edu/science /Estuary/sandworm.ht
m
Class Polychaeta
THE THREE GROUPS OF ANNELIDS (the segmented worms)
the earthworm Lumbricus terrestris
leech (Erpobdella?)
Class Clitellata
http//www.scibridge.sdsu.edu/ coursemats/introsci
/diversity/leeches.jpg
http//www.swgc.mun.ca/ biology/envs1000/chaines/
Subclass Oligochaeta
Subclass Hirudinoidea
6
KEY ANNELID FEATURES
segmentation, with segments clearly separated by
septa complex circulatory, excretory, sensory
systems live in a vast range of habitats, with a
staggering diversity of lifestyles, reproductive
strategies, etc. characterized by bristle-like
appendages called "chaetae" or "setae" (this
feature has been lost in the Hirudinoidea - the
leeches) typical "protostome" development
spiral cleavage usually with trocophore larva
and metamorphosis
Phragmatopoma trocophore
unidentified trocophore
Platynereis "setiger"
from Shankland Seaver (2000) PNAS, 974434-7
photos by Wim van Egmond http//www.microscopy-uk.
org.uk/mag/artmar99/polych.html
7
cross-section through an idealized polychaete worm
From Pechenik (2000) Fig. 13.3 Biology of the
Invertebrates
8
circulatory system
2 vessels (dorsal forward flow, ventral rear-word
flow) with an interconnected network of
veins no distinct heart
photo by J. Hodin
9
metanephridia - excretion in annelids
and whats this similar strucure?
from K. Schmidt-Nielsen Animal Physiology (1997).
from Jan A. Pechenik (2000) Fig. 13.2 Biology
of the Invertebrates