Nonetheless, placozoans show coordinated behavioral responses to chemicals emanating from their algal food, leading them to move toward food via ciliary gliding, externally digest the food, and take up the released nutrients.
Early molecular phylogenetic analyses generally recovered them as the sister group to cnidarians or ctenophores. Subsequent studies, using much higher numbers of independent genetic markers, indicated that they occupy a basal position within metazoans as the sister group to the Eumetozoa, being placed between sponges (phylum Porifera) and all other multicellular animals.
The latter seems to be the normal case for most bisexually reproducing animals, at least when they are dioecious. The storage of sperm allows a more rapid sexual response to a changing environment for example. The laboratory animals start to degrade when conditions become sub-optimal (Schwab K, 2003). Degrading animals reduce their lower epithelium and stop feeding.
All of the above is of crucial importance for the steadily increasing number of developmental genetic studies that want to use Trichoplax as a basal metazoan model system.
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