The phylum Priapulida is a small group of marine worms that is allied with the nematodes, kinorhynchs, loriciferans and nematomorphs in a clade called the Cycloneuralia or Introverta. Together with the arthropods they are generally considered to comprise the Ecdysozoa, a clade of moulting animals. A number of recent priapulid species possess features that resemble the predicted Ecdysozoan ancestor. In addition, recent molecular studies have also shown that they are basal within the Ecdysozoa/Cycloneuralia (Garey 2001, Webster et al. 2006). Their putative basal position thus makes priapulids highly interesting research objects for understanding the evolution of Ecdysozoa. Earlier investigations of the early embryology of the priapulid Priapulus caudatus are critically revised with the aid of modern techniques and equipment, confirming earlier studies that the early cleavages are highly symmetrical, total, subequal, radial and stereotypical. New results show that up to the sixth cleavage, the spindles are oriented along the animal/vegetal axis at both poles. This unique cleavage pattern has only limited similarities to other animals. During the sixth cleavage two cells move inwards and gastrulation commences. If the mesoderm is derived from both cells, its origin differs from that of many other protostomes…
Contents
INTRODUCTION
WHY STUDY PRIAPULIDS?
BACKGROUND
HISTORICAL OVERVIEW
MORPHOLOGY OF THE ADULT
GAMETES, FERTILIZATION AND DEVELOPMENT
ECOLOGY
PHYLOGENY
AIMS
METHODS
FIELDWORK
CULTIVATION TECHNIQUES
PREPARATION TECHNIQUES
MICROSCOPIC METHODS
UNPUBLISHED RESULTS
CONCLUSION
SVENSK SAMMANFATTNING
VARFÖR STUDERA PRIAPULIDER?
FÄLTARBETE
ARTIKLAR
REFERENCES
Author: Wennberg, Sofia A
Source: Uppsala University Library
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