Palæos:		Procoelomates
INVERTEBRATES		Machaeridia

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Class Machaeridia

Representative Orders

Class: Machaeridia 
	Order: Hercollepadida 
	Order: Turrilepadida 

Ken Kinman however provides the following classification:

Class Machaeridea
      1   Halkieriida
      ?   Chancelloriida (uncertain)
      2   Sachitida
      3   Tommotiida
      4   Turrilepadida
      5   Hercolepadida

Note that this incorporates a number of forms normally included in the Coeloscleritophora

References

References

Dzik, J. 1986b. Turrilepadida and other Machaeridia. In: A. Hoffman & M.H. Nitecki (eds.) Problematic Fossil Taxa, 116-134. Oxford University Press, New York.

Notes

 Abstracts, He - Ho (5/17/01)

BODYPLAN OF THE PROBLEMATIC METAZOAN MACHAERIDIA

HÖGSTRÖM, Anette, Dept. of Earth Sciences, University of California, Riverside, CA, USA

"Enigmatic scleritome-bearing metazoans such as the Machaeridia constitute formidable challenges from several perspectives. All scleritomes suffer the same preservational problems in that they very easily disarticulate after the organism dies making isolated sclerites and sclerite fragments the most common form of preservation and a limiting factor when reconstructing morphology and anatomy of the organism.

Machaeridian scleritomes range from relatively straightforward types forming a dorsal cover to complex ones, more or less enveloping the entire animal. However, all scleritomes are composed of 2­4 longitudinal series of calcitic sclerites. The complex scleritome of lepidocoleid machaeridians closes and opens along the ventral side and also allows the animal to enroll spirally for protection, suggesting a segmented bodyplan, although not strictly metameric.

Epimorphic development of the machaeridian scleritome, with all sclerite segments present initially, is supported by the uniform appearance of ornamentation and growth lines, and the presence of occasional growth increments traceable between sclerites in articulated specimens. This is in contrast to the adding of sclerites through development in other scleritome-bearing taxa, as seems to be the case in coeloscleritophorans, but Halkieria does also exhibit shells growing by accretion.

The bodyplan of machaeridians does not agree with the concept of Ecdysozoa as a clade of molting animals and thus rules out possible affinities with the arthropods. However, an inclusion within the Lophotrochozoa clade does not resolve the problem of machaeridian affinities to a higher degree, but tentatively places machaeridians as a stem group to the molluscs or the annelids.

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