worms1.ppt

7/27/2019 worms1.ppt

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functions of different animal coeloms

1) simple circulatory system2) increase in body size possible (follows from 1)

3) storage area for organs, separates organs from gut

4) independent growth of organs possible (e.g. coelomic spaceallows storage of gametes, seasonal reproduction enhanced)

5) allows for developmental/physiological coordination via

circulating hormones

6) hydrostatic skeleton - burrowing!

7) also allows for eversible mechanisms, such as annelid

proboscis, and hence diverse feeding methods can evolve


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from: Ruiz-Trillo et al. (1999)Science283: 1919.

one recent Metazoan phylogeny (molecular data)

ANNELIDA

ECHIURA

POGONOPHORA

SIPUNCULA

CHAETOGNATHA

NEMERTEAMOLLUSCA

BRACHIOPODA

BRYOZOA

PHORONIDA

PLATYHELMINTHES

(worms in red)


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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...)

WHY WORM?


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THE THREE GROUPSOF ANNELIDS

(the segmented worms)

Class Polychaeta

the sand wormNereis vexillosa

http://www.lanecc.edu/science

/Estuary/sandworm.htm

Class Clitellata

Subclass Oligochaeta

the parchment worm

Chaetopterus variopedatus

photo by Erling Svensenwww.uwphoto.no

http://www.scibridge.sdsu.edu/

coursemats/introsci/diversity/leeches.jpg

the earthwormLumbricus terrestris

http://www.swgc.mun.ca/

biology/envs1000/chaines/

leech (Erpobdella?)

Subclass Hirudinoidea


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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 Platynereis "setiger"unidentifiedtrocophore

photos by Wim van Egmond http://www.microscopy-uk.org.uk/mag/artmar99/polych.htmlfrom Shankland & Seaver (2000)

PNAS 97:4434-7


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From: Pechenik(2000) Fig. 13.3Biology of theInvertebrates

cross-section through an idealized polychaete worm


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2 vessels (dorsal forward flow, ventral rear-word flow)

with an interconnected network of veins

no distinct heart

photo by J. Hodin

circulatory system


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metanephridia - excretion in annelids

from: Jan A. Pechenik (2000) Fig. 13.2Biology of the Invertebrates

and whats this similar strucure?

from: K. Schmidt-NielsenAnimal Physiology (1997).

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worms1.ppt