Zoomorphologie

, 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
Article

Summary

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.

Keywords

Fiber Bundle Mouth Opening Sense Organ Sensory Cell Head Region 

List of Abbreviations

ALSF

anterio-lateral sensory field

BC

body cavity

C

ciliary region

CB

ciliary base

CL

cuticular lining of the anterior foregut

COSF

circum-oral sensory field

CP

cuticular projection (SOSR)

CU

cuticle

(CU)

cuticular material in the SOSR

D

beltdesmosome (= zonula adhaerens)

DB

dense body (type 1 sensory cell — SOSR)

E

epidermal cell

F

filaments

IE

inner layer of epicuticle

IS

inner dendritic segment

J

intercellular compartment between OS3(COSF) and E

M

mouth tube

MC

mouth cavity

ML

mouth lamellae

MO

mouth opening

MT

microtubules

MV

microvilli

O

outer layer of intracuticle

OE

outer layer of epicuticle

OS

outer dendritic segment

P

pores

PC

procuticle

PO

pharyngeal organ

RS

receptor lymph space

SS

stylet sheaths

SOSR

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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