, Volume 89, Issue 1, pp 1–19 | Cite as

Electron microscopic investigation of cephalic sense organs of the tardigradeMacrobiotus hufelandi C.A.S. Schultze

  • Bernd Walz


In the anterior head region ofMacrobiotus hufelandi four sensory regions were identified, and a detailed description of their fine structure follows. According to their position in the head region the sensory regions were called; I. anterio-lateral sensory field (ALSF), II. circum-oral sensory field (COSF), III. sub-oral sensory region (SOSR), and IV. pharyngeal organ (PO).

The ALSF is innervated by three pairs of fiber bundles made up of dendrites. These bundles originate in the brain, pass foreward laterally, and widen, brushlike, under the epidermis. The COSF circumscribes the whole mouth opening. Under the specialized cuticle of the COSF, dendrites of three sensory cell types (type 1–3) terminate. The SOSR surrounds the anterior cuticular ring of the mouth cavity. It is also innervated by dendrites of three sensory cell types (type 1–3). The dendrites are arranged arround the mouth cavity in ten groups, each group being composed of three. Each dendritic triplet contains the sensory cell types 1–3. The PO is represented by four cuticular pockets. These are located at the transition between mouth cavity and mouth tube and innervated by 3–5 dendrites each. The cuticular pockets enclose considerable receptor lymph cavities which communicate with the lumen of the anterior foregut over multiple pores.

With regard to the possible functions of the four sensory regions, the ALSF is discussed as a mechanoreceptive organ. The type 1 sensory cells in the COSF are suggested to be chemoreceptive and the type 2 sensory cells to serve as me-chanoreceptors in the COSF. For the sensory cells of type 1 in the SOSR, a movement of the anterior cuticular ring of the mouth cavity is considered to be adequate (mechanical) stimulus. The PO is thought to be a chemoreceptive sense organ.


Fiber Bundle Mouth Opening Sense Organ Sensory Cell Head Region 
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List of Abbreviations


anterio-lateral sensory field


body cavity


ciliary region


ciliary base


cuticular lining of the anterior foregut


circum-oral sensory field


cuticular projection (SOSR)




cuticular material in the SOSR


beltdesmosome (= zonula adhaerens)


dense body (type 1 sensory cell — SOSR)


epidermal cell




inner layer of epicuticle


inner dendritic segment


intercellular compartment between OS3(COSF) and E


mouth tube


mouth cavity


mouth lamellae


mouth opening






outer layer of intracuticle


outer layer of epicuticle


outer dendritic segment






pharyngeal organ


receptor lymph space


stylet sheaths


sub-oral sensory region


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Copyright information

© Springer-Verlag 1978

Authors and Affiliations

  • Bernd Walz
    • 1
  1. 1.Lehrstuhl für Zellenlehre der Universität HeidelbergHeidelbergFederal Republic of Germany

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