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 Gastrotricha
"Hairy Stomach"

photo from http://hooge.developmentalbiology.com/meiofauna/
 
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This phylum's 'place'
relative to other phyla:
  • Metazoan
    • Triploblast
      • Uncertain affiliation??????
Selected taxa within this taxon:
 
(you are not responsible for any classes in this phylum)

~400 species
 

Body Plan    
 



Natural history


Phylogeny
Several hypotheses:

1) Nematodes affiliation based on pseudocoelom. Has the value of using coelomic condition in invertebrate phylogeny been called into question?
 

2) Rotifers affiliation gastrotrichs based on shared characteristic that include external cilia, lack of segmentation, lack of circulatory system, and no true coelom.  Why should we be cautious about using these characteristics?  Parathenogentic as seen in rotifers.  Head bears sensory bristles, but resemblance to rotifers is superficial; gastrotrichs lack jaws and  lack intracellular cuticle (non-molting cuticle is external in gastrotrichs),
 

3) Platyhelminthes affiliation based more morphological characters linking them with flatworms than with nematodes. Which of the above characteristics? Comparisons of 18S rDNA sequences by Wirz et al. (1999) indicate that Gastrotricha are not closely related to either Nematoda or Rotifera. The exact position of Gastrotricha remains unresolved, but some analyses of 18S rDNA sequences place them within Spiralia near Platyhelminthes.
 

Cleavage is radial.   How would this have lead to confusion in the older, traditional phylogenetic scheme?
 
 
 
 
 
Lecture Sources:
  • Pechenik. Jan A.  2000. Biology of the Invertebrates.  McGraw-Hill, New York.


 
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