Research Article |
Corresponding author: Leif Moritz ( moritz.leif@gmail.com ) Academic editor: Zoltan Korsós
© 2020 Leif Moritz, Markus Koch.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Moritz L, Koch M (2020) No Tömösváry organ in flat backed millipedes (Diplopoda, Polydesmida). In: Korsós Z, Dányi L (Eds) Proceedings of the 18th International Congress of Myriapodology, Budapest, Hungary. ZooKeys 930: 103-115. https://doi.org/10.3897/zookeys.930.48438
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The Tömösváry organ is a sensory structure of the head in myriapods and some other terrestrial arthropods. Due to its variable shape, size, and position in millipedes (Diplopoda) the Tömösváry organ is commonly used as diagnostic character in taxonomic descriptions and often included in phylogenetic analyses. For the Polydesmida, the largest millipede order, the Tömösváry organ is inconsistently stated as being either absent or present as a pear-shaped pit covered by a membrane or cuticular disc. In order to resolve this inconsistency, we investigated the morphology of the presumable Tömösváry organ in four polydesmidan species based on paraffin-histology, semi-thin sections and micro-computed tomography. Our results unambiguously favor the view that the articulation of the cephalic tentorium with the head capsule was misidentified as the Tömösváry organ in previous studies, and thus that the Tömösváry organ indeed is absent in the Polydesmida. The pear-shaped pit proved to represent the distal roundish expansion of the incisura lateralis, to which – similarly as in julidan millipedes – the tentorial transverse bar is articulated. The absence of the Tömösváry organ in the Polydesmida does not affect the topology of the interrelationships among the millipede orders retrieved in previous cladistic analyses based on morphology. As a character shared by Colobognatha and Juliformia, however, absence of a Tömösváry organ in Polydesmida favors the optimization of its presence in nematophoran millipedes as a reversal. Further studies are needed to clarify whether among chilognathan millipedes a Tömösváry organ really exists in taxa such as Stemmiulida, and whether the Tömösváry organs are homologous across millipedes.
Anatomy, Histology, Micro-Computed Tomography, Morphology, Tentorium
The Tömösváry organ is a paired sensory organ, situated on the head of millipedes (Diplopoda) and other Myriapoda posterior of the antennal base. It is also referred to as postantennal organ (e.g.,
Tömösváry organs can be present in various shapes, forming a groove, pit or tube (
The order Polydesmida is the most diverse order of the millipedes (Diplopoda), with more than 5000 described species (
There is uncertainty about the absence or presence of the Tömösváry organ in the Polydesmida. Its presence in Polydesmida was first stated by
In this study we aim to clarify whether the Tömösváry organ is present or absent in the Polydesmida, and which structure was originally described by
Four species representing four families (Polydesmidae, Paradoxosomatidae, Oxydesmidae, Gomphodesmidae) and three suborders (Polydesmidea, Strongylosomatidea, Leptodesmidea) were investigated. Specimens of Polydesmus angustus (Latzel, 1884) were collected in April 2015 in the Kottenforst (50°41'05.3"N, 07°05'19.4"E, Bonn, Germany) and fixed in Bouin-solution for paraffin-histology and micro-CT scanning, or in Karnovsky fixative (2.5% glutaraldehyde, 3.2% paraformaldehyde in 0.1M salted phosphate buffer, pH 7.2) for semi-thin sections. Furthermore, for investigations with micro-CT only, specimens of Oxidus gracilis (Koch, C. L., 1847) (collected in the Botanical Garden of the University of Bonn, Germany in April 2018), Coromus vittatus (Cook, 1896) (obtained via the pet trade from Nigeria) and Tymbodesmus sp. (obtained via the pet trade from Cameroon) were fixed in Bouin-solution. Micro-CT data and histological images of Polydesmus angustus are deposited on Morphobank (
ID | Location | Voltage | Current | Pixel size | Exposure | Rotation steps | Rotation | Averaging | |
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Polydesmus angustus |
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Kottenforst, Bonn, Germany | 40 kV | 200 µA | 2.6 µm | 1659 ms | 0.1° | 180° | 7 |
Oxidus gracilis |
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Botanical garden, Bonn, Germany | 50 kV | 200 µA | 1.2 µm | 500 ms | 0.1° | 180° | 7 |
Coromus vittatus |
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Pet trade, Nigeria | 60 kV | 166 µA | 3.6 µm | 500 ms | 0.1° | 180° | 7 |
Tymbodesmus sp. |
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Pet trade, Cameroon | 43 kV | 200 µA | 1.8 µm | 1800 ms | 0.15° | 360° | 10 |
Following
For micro-CT scanning one specimen each fixed in Bouin-solution of Polydesmus angustus (Latzel, 1884), Oxidus gracilis (Koch, C. L., 1847), Coromus vittatus (Cook, 1896) and Tymbodesmus sp. were transferred to 96% ethanol via an ascending ethanol series and stained with 3% Iodine solution for 24 hours. The specimens were washed in 100% ethanol and critical point dried using a Leica EM CPD 300. Micro-CT scanning was performed at the
In all studied species the structure described as Tömösváry organ (Fig.
Polydesmus angustus, head A–D volume rendering based on micro-CT data: A Frontal view B cross-section, posterior view, plane indicated in C C lateral view D sagittal view, cutting plane indicated in A E–G details of connection of tentorial transverse bar to head capsule at incisura lateralis, plane as indicated in D: E histological section (Paraffin, Azan-staining) F histological section (Araldite, Toluidine blue) G optical section of micro-CT scan. Abbreviations: at = antenna, co = collum, eb = epipharyngeal bar of tentorium, gc = gnathochilarium, gls = gnathal lobe sclerite, hc = head capsule, il = incisura lateralis, la = labrum, mc = mandibular cardo, mg = mandibular gnathal lobe, ms = mandibular stipes, pp = posterior process of tentorium, tb = transverse bar of tentorium. Asterisk (*) indicates structure previously interpreted by
Articulation of the tentorial transverse bar to the head capsule in the Polydesmida A–C head in lateral view (anterior is left), volume rendering D–F head, sagittal section through tentorial transverse bar, volume rendering A, D, G Oxidus gracilis B, E, H Coromus vittatus C, F, I Tymbodesmus sp. J Polydesmus angustus G–J optical cross sections K, L the Tömösváry organ in Eurydesmus laxus after
The general structure of the tentorium of the studied species is the same as described by
Attached on the distal margin of the posterior process is the posterior tentorial muscle (t3), which originates from the postoccipital flange, and the ventral tentorial muscle (t4), which originates from the transverse mandibular tendon (see Suppl. material
Polydesmus angustus, histological sections from anterior (A) to posterior (D) A articulation of tentorial transverse bar to head capsule B tentorial transverse bar and epipharyngeal bar C tentorial hypopharyngeal bar and posterior process D articulation of tentorium to “Nebententorium”. Abbreviations: a2 = medial antennal muscle, a3 = lateral antennal muscle, a4 = anterior antennal muscle, asd = duct of anterior salivary gland, asg = anterior salivary gland, co = collum, eb = epipharyngeal bar of tentorium, gl = mandibular gnathal lobe, gls = gnathal lobe sclerite, hb = hypopharyngeal bar of tentorium, m1 = gnathal lobe sclerite muscle, m4 = anterior mandibular cardo muscle, m5 = posterior mandibular cardo muscle, mc = mandibular cardo, mes = median septum, mg = mandibular gnathal lobe, ms = mandibular stipes, nt = ‘Nebententorium’, pc = preoral chamber, ph = pharynx, po = ‘Presshöcker’, t1 = anterior tentorial muscle, t2 = dorsal tentorial muscle, tb = transverse bar of tentorium. Scale bars: 200 µm.
This conclusion (absence of the Tömösváry organ in the Polydesmida) is further supported by previous doubts on the presence of a nervus tömösváryi in the Polydesmida (
The absence of the Tömösváry organ in the Polydesmida is a character shared with the Colobognatha, Stemmiulida, Juliformia and Siphoniulida among the chilognathan millipedes (
Contrary to several old and recent publications (e.g.,
We are grateful to W. A. Shear and S. Golovatch as well as to one anonymous reviewer for their valuable comments on our manuscript. We thank Tatjana Bartz and Christiane Wallnisch (Institute of Evolutionary Biology and Ecology (IEZ), Univ. Bonn) for their assistance in the histological work, and Pia Schucht (Institute of Zoology (IZ), Univ. Bonn) and Juliane Romahn (Zoological Research Museum A. Koenig (
Polydesmus angustus, head capsule and tentorium with associated musculature
Data type: multimedia