Muscular Arrangement and Sclerite Morphology in the Haptor of Tetraonchus monenteron (Monogenea, Dactylogyridea)

Abstract

Background 

Tetraonchidae is a small and relatively monomorphic family of dactylogyroid monogeneans. Since the morphology of sclerites of the attachment organ (haptor) is one of the primary criteria in tetraonchid taxonomy, the confocal study of sclerites and associated musculature may provide valuable taxonomic information.

Purpose 

The aim of this study was to examine the haptoral sclerites and musculature in Tetraonchus monenteron (Wagener, 1857), a common parasite of pike.

Methods

Haptoral musculature of T. monenteron was studied using phalloidin staining and confocal microscopy, with sclerites visualized in the reflection confocal mode.

Results

Haptoral armature of T. monenteron consists of ventral and dorsal pairs of anchors, a ventral bar, eight pairs of marginal hooks and at least three pairs of accessory sclerites. Anchors are operated by 14 muscles, of which the most prominent are extrinsic muscles, the transverse muscle interconnecting the ventral anchors, three muscles connecting the ventral anchor to the ventral bar, and four muscles of the dorsal and ventral anchors inserting on the haptoral wall. The extrinsic muscles are attached to the braceshaped sclerites, which in turn are connected to the dorsal anchors via muscle bundles.

Conclusion

The gaffing action of the dorsal anchors is likely to be achieved by the extrinsic muscles and the transverse muscle that clamps the extrinsic muscles against the body wall. The ventral anchors are probably held in attached position by the transverse muscle and four muscles inserting on the ventral bar and haptoral wall. The haptoral musculature may have potential utility for tetraonchid taxonomy.

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Abbreviations

ar:

Anterior ridge of the ventral bar

bas:

Ball-shaped sclerite

bd:

Blade of the dorsal anchor

brm:

Muscle bundles of the brace-shaped sclerites

brs:

Brace-shaped sclerite

bv:

Blade of the ventral anchor

cb:

Central bridge of the ventral bar

da:

Dorsal anchor

daf1-2:

Muscles connecting the dorsal anchor to flabellate sclerite

daw1-2:

Muscles connecting the dorsal anchor to the body wall

de:

Dorsal branch of the extrinsic muscles

div1-2:

Muscles connecting the ipsilateral dorsal and ventral anchors

dov:

Muscle connecting the opposite dorsal and ventral anchors

ex:

Extrinsic muscles

fl:

Filament loop

flm:

Muscle of the filament loop

fs:

Flabellate sclerite

h:

Haptor

id:

Inner root of the dorsal anchor

ld:

Fibrous loop of the dorsal anchor

le1-3:

Lateral branches of the extrinsic muscles

lv:

Fibrous loop of the ventral anchor

mb:

Blade of the marginal hook

mh:

Marginal hook

mp:

Protractor muscle of the marginal hook

mr:

Medial ridge

ms:

Shaft of the marginal hook

ov:

Outer root of the ventral anchor

pe:

Posterior endings of the extrinsic muscles

ph:

Pharynx

rid:

Ridge on the inner root of the dorsal anchor

riv:

Ridge on the inner root of the ventral anchor

rod:

Ridge on the outer root of the dorsal anchor

rov:

Ridge on the outer root of the ventral anchor

rpm:

Retractor muscle of the hook-bearing papilla

th:

Thumb of sickle

thm:

Thumb muscle

tid:

Tip of the inner root of the dorsal anchor

tiv:

Tip of the inner root of the ventral anchor

tod:

Tip of the outer root of the dorsal anchor

tov:

Tip of the outer root of the ventral anchor

va:

Ventral anchor

vat:

Transverse muscle of the ventral anchors

vav1-3:

Muscles connecting the ventral anchor and the ventral bar

vaw:

Muscle connecting the ventral anchor to the body wall

vb:

Ventral bar

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Acknowledgements

This work was supported by budget funding of the Russian Academy of Sciences (projects AAAA-A17-117030110029-3 and AAAA-A17-117030310322-3). Confocal microscopy was performed at the “Taxon” Research Resource Centre (Zoological Institute RAS) (http://www.ckp-rf.ru/ckp/3038/).

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Correspondence to Anatoly A. Petrov.

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Petrov, A.A., Gerasev, P.I. Muscular Arrangement and Sclerite Morphology in the Haptor of Tetraonchus monenteron (Monogenea, Dactylogyridea). Acta Parasit. 64, 138–147 (2019). https://doi.org/10.2478/s11686-018-00015-7

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Keywords

  • Tetraonchus
  • Haptor
  • Muscles
  • Sclerites
  • Confocal microscopy
  • Phalloidin