• Steffen Harzsch
  • Carsten H. G. Müller
  • Yvan Perez


According to palaeontological evidence, the Chaetognatha (arrow worms), a group of small marine predators that are major components of the zooplankton throughout our world oceans, were present already in the Early Cambrian (approx. 540–520 Myr years ago), namely, as Chengjiang biota, but have also been documented in the Middle Cambrian Burgess Shale. The so-called protoconodonts, spine-like, small, shelly microfossil elements that were abundant in the Cambrian, are today convincingly interpreted as parts of the chaetognath grasping apparatus or, at least, as belonging to protoconodont animals most closely related to Chaetognatha (e.g., Szaniawski 1982, 2002, 2005; Vannier et al. 2007; but see Conway Morris 2009; Szaniawski 2009 for a controversial discussion). The presence of protoconodonts in the lowermost Cambrian and the complexity of their feeding apparatus points to a Precambrian origin of these animals. These authors also suggested placing them among the earliest active predator metazoans and argued that the ancestral chaetognaths were planktonic with possible ecological preferences for hyperbenthic niches close to the sea bottom. Today, the taxon Chaetognatha comprises more than 150 described species from all geographical and vertical ranges of the ocean. They are characterised by an elongated, streamlined body; the presence of horizontally projecting fins; and, at the anterior end, two groups of moveable, cuticularised grasping spines used in capturing prey such as copepods (Fig. 10.1). With a body length between just a few millimetres up to 120 mm, these glassily transparent carnivores are among the most abundant planktonic organisms, but several epibenthic species are also known.


Germ Plasm Mesodermal Cell Coelomic Cavity ParaHox Gene Stomatogastric Nervous System 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We would like to thank Verena Rieger for her contribution to the experimental work on nervous system development reported here and Tina Kirchhoff for editing the reference list. We gratefully acknowledge the exchange with Thurston Lacalli and Andreas Hejnol on metazoan gastrulation patterns, Carolin and Joachim Haug on fossil chaetognaths, and Günter Purschke on photoreceptor structure. Research on arrow worms by SH was supported by grants HA 2540/7-1, 2, 3 in the DFG focus programme “Metazoan Deep Phylogeny”.


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Copyright information

© Springer-Verlag Wien 2015

Authors and Affiliations

  • Steffen Harzsch
    • 1
  • Carsten H. G. Müller
    • 2
  • Yvan Perez
    • 3
  1. 1.Department of Cytology and Evolutionary Biology, Zoological Institute and MuseumErnst-Moritz-Arndt-University GreifswaldGreifswaldGermany
  2. 2.Department of General and Systematic Zoology, Zoological Institute and MuseumErnst-Moritz-Arndt-University GreifswaldGreifswaldGermany
  3. 3.Aix-Marseille Université, CNRS, IRD, Avignon Université, IMBE UMR 7263MarseilleFrance

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