http://www.collembola.org/publicat/onychiur.htm
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Last updated on
2021.01.23
by Frans Janssens
Frans Janssens,
Department of Biology, University of Antwerp, Antwerp, B-2020, Belgium
Abstract.
To be completed.
Introduction
To be completed.
Furcal musculature
The furcal musculature is characterised by 3 types of muscles that can be
organised in 2 groups :
1. the direct group of 2 muscles that operate directly on the furca,
2. the indirect group that operates the furca indirectly by increasing
the hydraulic pressure of the hemolymph in the abdomen.
The direct group comprises 2 types of muscles :
1. the musculus extensor furcae extends the furca backwards and is inserted
at the posterior margin of the manubrium,
2. the musculus flexor furcae folds the furca back underneath the ventrum,
winds up the spring mechanism and is
inserted at the anterior margin of the manubrium.
The indirect group comprises 1 type of muscle :
1. the musculus levator furcae increases the hydraulic pressure of the
hemolymph and is inserted in front of the furcula
at the sternite of the fourth abdominal segment.
In addition to the loaded springmechanism, both the extensor and the
levator muscles cooperate in extending the furcula backwards to effectuate
the jump.
Reduction of the furcal muscles in Onychiurinae
In his comparative study of the muscular anatomy of the saltatory apparatus
of Collembola, Pistor (1955:533-536)
concluded that the differences in furcal muscles in Orchesella villosa,
Folsomia sexoculata
and Onychiurus armatus (now Protaphorura armata) form a reduction
series.
The musculus extensor furcae (ext.f.) is present in all species, even in
Protaphorura armata (Fig.Oa. red *),
where the furcula itself is absent (Pistor, 1955:533).
The dorsoventral muscle e of Protaphorura armata is homolog to and is
considered as the final reductionproduct of the original musculus flexor furcae
(Pistor, 1955:533-535).
The dorsoventral muscles p of Protaphorura armata are homolog to and are
considered as the final reductionproduct of the original musculus levator furcae
(Pistor, 1955:535).
The distinct furcal muscle groups remain as a functionless relict in
Protaphorura armata (Pistor, 1955:535,Abb.20,21).
Contradictions in the reduction series hypothesis of Pistor (1955)
The number of muscles in the fourth abdominal segment is highest
in Protaphorura : 7.
(5 in Folsomia, 3 in Orchesella (longitudinal muscles excluded))
(Pistor, 1955:530:Tab.1).
So in the most reduced form,
the most complex musculature would be present...?
In Orchesella, the musculus longitudinalis ventralis ends after the muscle
of the retinaculum and before the ventral insert of the musculus levator furcae
(thus it does not continue to the end of the abdomen, given it would then
disturb the furcal musculature)
(Pistor, 1955:518).
In Folsomia, the musculus longitudinalis ventralis ends at the anterior
base of the furca (thus it continues further posteriorly into the fourth
abdominal segment then in Orchesella) (Pistor, 1955:521).
In Protaphorura, the ventral longitudinal muscles (Fig.Oa. blue)
continue up to the begin of the sixth abdominal segment (Pistor, 1955:525).
This condition is the plesiomorph condition in Arthropoda.
So in the most derived form,
the plesiomorph condition would apply...?
In Protaphorura, the oblique intersegmental muscle dv.i (Fig.Oa. yellow) is
present in the fourth abdominal segment, while it is absent in Folsomia
and Orchesella (Pistor, 1955:534,Abb.21).
This muscle represents the plesiomorph condition given it is present in
the first to third abdominal segments.
So in the most reduced form,
the most plesiomorph condition would apply...?
In contradiction with Pistor (1955) we conclude that Onychiurinae are not the
final stage in a reduction series of the furcula
in the Collembola (Orchesella -> Folsomia -> Protaphorura)
but a more plesiomorph form in which a reduction of the furcula
independently occured.
As such we comply with Handlirsch (1926), who considered the reduction of the
furca in the different
families of the Collembola as a parallel evolution (Pistor, 1955:533).
Remnant furcal extensor muscle
Fig.Oa. Onychiurus armatus from Germany
Abd.4 muscles (*)
Modified after Pistor, D. 1955 Abb.11
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Fig.KWP2. Furcal fovae in Protaphorura vasilinae
Modified after Kaprus, I., Weiner, W.M. & Pasnik, G. 2016 Fig.57
 |
The musculus extensor furcae (ext.f.) is present in
Protaphorura armata (Fig.Oa. red *),
where the furcula itself is absent (Pistor, 1955:533).
The musculi extensor furcae found in Protaphorura by Pistor (1955)
are the relict remains of the furcal extensor muscles of the ancestor of the
Onychiuridae, having a furcula.
The oval areas of fine granulation, the fovae, mark the locations where
the muscles are attached to the exoskeleton.
In Protaphorura vasilinae, at the 4th abdominal sternum,
the group of 3 fovae, in the posterior left and right corners of
the manubrial field,
mark the attachement of the ancestral remains of the
musculi extensor furcae (Fig.KWP2).
* For clarification of abreviations used in the schematic image
see Pistor (1955:538-539).
Fig.Ms. Mesaphorura sylvatica from Russia
Abd.4 muscles (*)
Modified after Panina, I.V. & al. 2019 Fig.6A
 |
In an anatomic study of Mesaphorura sylvatica, Panina & al. (2019:15)
found an intersegmental muscle of abd.4 'AIVism1-3' (Fig.Ms red *)
that matches the remnant furcal extensor muscle as described by Pistor (1955)
in Protaphorura armata.
Thus also in Tullbergiidae, a closely to the Onychiuridae related family,
the remnant furcal extensor muscle is present
while the furcula itself is completely absent.
* For clarification of abreviations used in the schematic image
see Panina & al (2019:16-17).
The ventral insertion of the remnant furcal extensor muscle is located at the
posterior margin of abd.4, both in Protaphorura armata
and Mesaphorura sylvatica.
This kind of contradicts with the anterior position of the furcal area in
Onychiurinae as described by Pomorski (1998:5,Fig.1) (Fig.On,Sf,Kb).
Reduction of the furcula in Onychiurinae
The Onychiurinae do never jump and their saltatory apparatus is always reduced,
in variable degree of reduction (Pomorski, 1998:16).
The reduction series of the saltatory apparatus
(modified after Pomorski, 1998:16-18):
Fig.Of1. Onychiurus furciferus from Poland
Vestigial furcula; ventral view
After Stach, J.. 1954 Plate XIII Fig.3
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Fig.Of. Onychiurus furciferus from South Germany
Vestigial furcula; ventral view
Modified after Gisin, H. 1960 Abb.222
 |
1. manubrium accreted to sternite has the form of plate with several setae;
two very short papilla-like dentes with 3-4 setae; tiny, vestigial mucrones;
small, bidentate retinaculum
(Pomorski, 1998:20,Fig.41) (Fig.Of,Of1,Of2) : Supraphorura.
Fig.Of2. Onychiurus furciferus from Poland
Vestigial furcula; lateral view
After Stach, J.. 1954 Plate XIII Fig.4
 |
Fig.Ot. Onychiurus tuberculata ♂ & ♀ from Poland
Vestigial furcula; ventral view
After Stach, J.. 1954 Plate X Fig.6 & 7
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Fig.Ob. Onychiurus burmeisteri from Switzerland
Vestigial furcula; lateral view
Modified after Gisin, H. 1960 Abb.223
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2. loss of mucro; dentes retaining form of paired, papillate appendices
(Pomorski, 1998:20,Fig.42) (Fig.Ob,Ot) : Kalaphorura. And Psyllaphorura.
Fig.Or. Onychiurus rectospinatus from Poland
Remnant furcula; ventral view
Parapseudocelli at third abdominal sternum
After Pomorski, R.J. Fig.431
 |
3. loss of dentes and retinaculum;
trace of finer granulation mark original position of
furcula (Pomorski, 1998:20,Fig.45-48); bipartite origin of furcula
often still visible (Fig.Or) :
e.g. Onychiurus, Orthonychiurus, Detriturus, Hymenaphorura, Heteraphorura,
Thalassaphorura, Tantulonychiurus, Agraphorura.
In Heteraphorura and Hymenaphorura,
the furcal area is translocated posteriorly
to make space for the male ventral organ.
Note : "In adults the remnants of the furca and especially the chaetotaxy are
not always possible to describe precisely because of disturbances resulting from
numerous additional setae and rather frequent aberrations.
In juveniles the chaetotaxy is fully legible,
but it is difficult to collect or raise I instar larvae."
(Pomorski, 1998:18).
Fig.Os. Onychiurus schoetti from Poland
Remnant furcula; ventral view
After Stach, J.. 1954 Plate III Fig.5
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Fig.Op2. Onychiurus prolatus from Europe
Remnant furcula; lateral view
After Gisin, H. 1960 Abb.224 up
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4. loss of bipartite origin of furcula;
the anterior margin of the finer cuticular granulation is folded inwards
to form an unpaired epidermal fold marked with setae
(Pomorski, 1998:20,Fig.43,44) (Gisin, 1960:112,Abb.224) (Fig.Op2,Os);
the furcal area is often translocated to the middle of the sternum
to make space for the male ventral organ :
e.g. Protaphorura, Bionychiurus, Archaphorura, Oligaphorura, Micraphorura,
Heteronychiurus, Onychiurus(partim).
Furcal area
Fig.Tb. Tetrodontophora bielanensis from Czechia
Furcal area; ventral view
2008.04.21 © Deml, M.
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Fig.H. Hypogastrura sp. from France
Furcal area; ventro-lateral view
Retinaculum of 3rd abdominal sternum (*)
2018.02.18 © Picard, J.
 |
In Tetrodontophora, a more plesiomorph species of Onychiuridae,
the furcal area is located in the posterior half
of the fourth abdominal sternum (Fig.Tb).
The broad base of the furcula, the manubrium, is inserted ventrally near to
the posterior margin of the fourth abdominal segment.
Also in all other Collembola with a functional furca, the furcal area is
located in the
posterior half of the fourth abdominal sternum (Fig.H).
Therefore, this condition is considered the plesiomorph condition
for the furcal area.
Fig.On. Onychiurinae from Poland
Furcal area; lateral view
Modified after Pomorski, R.J. 1998 Fig.1
 |
According to Pomorski (1998:5,Fig.1), in Onychiurinae,
the furcal area is located
near the anterior margin of the anterior half of
the fourth abdominal sternum (Fig.On) (see also Fig.Sf,Kb).
Fig.Sf. Supraphorura furcifera from the UK
Furcal area; lateral view
Modified after Hopkin, S.P. 2007 Fig.25a
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Fig.Kb. Kalaphorura burmeisteri from the UK
Furcal area; lateral view
Modified after Hopkin, S.P. 2007 Fig.24a
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This contradicts with the findings of Pistor (1955), who found
relict furcal extensor muscles in Protaphorura that are inserted ventrally
at the posterior margin of the fourth abdominal sternum (Fig.Oa,red),
and which are as such without function, given the basis of
the remnant of the furcula of the Onychiurinae is not
inserted at the posterior margin but at the anterior margin of the sternum.
Therefore, this latter condition is considered the derived,
apomorph condition for the furcal area.
Fig.Ps. Paranurophorus simplex from Holland
2018.02.18 © Kamsteeg, G.
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Fig.Cs. Coloburella simplex from Switzerland
Furcal area; lateral view
Modified after Gisin, H. 1960 Abb.316
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Remarkably, in Paranurophorus simplex (Fig.Ps),
an Isotomidae with an Onychiurinae-like habitus
(due to a convergent evolution in the same subsoil habitat),
the furcal area is also located at the anterior margin
of the fourth abdominal sternum.
The furcula itself has been reduced to a pair of half spherical papillae,
as in Kalaphorura,
but now each with a short cephalad spine (remnant mucro of reduced dens);
the retinaculum is absent (Gisin, 1960:168,169,170) (Fig.Cs).
It is not known whether or not a remnant furcal extensor muscle is present.
Fig.Hj. Heteronychiurus januarii from Poland
Furcal area; ventral view
Modified after Pomorski, R.J. 1998 Fig.53
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We do not agree with Pomorski (1998) that the furcal area of Onychiurinae is
located at the anterior margin of the fourth abdominal sternum. That is only
true in part. In many Onychiurinae the furcal area is translocated caudad
about half way of the fourth abdominal sternum (Fig.Hj).
E.g. in Heteronychiurus januarii, in front of the remnant furcal
fold, 3 rows of setae are inserted (in males they are part of the so-called
male ventral organ) (Fig.Hj).
Attested terminology wrt the furcula in Onychiuridae
small semicircular integumentary fold : Stach 1954:6
rudiments of furcula : Stach 1954:86,106,111
reduced furcula : integumentary semicircular fold : Stach 1954:92,124,139
trace of reduced furcula : Stach 1954:95,104
cuticular trace of furca : Babenko & Fjellberg 2015:71
furcula reduced : wart-like dentes : Stach 1954:114
furca reduced : small area of fine granulation Babenko & Fjellberg 2015:52,54
rudiments of furcula : wart-like tubercles : Stach 1954:121-122
furcula weakly developed: Stach 1954:135
furca : as small cuticular furrow Babenko & Fjellberg 2015:57
furca : as small area with fine granulation Babenko & Fjellberg 2015:59
furca : shaped like a small fold Babenko & Fjellberg 2015:65
furca remnant : as small fold Babenko & Fjellberg 2015:61
area furcalis : Pomorski 1996 cited from Babenko & Fjellberg 2015:49,63
furcal area : Babenko & Fjellberg 2015:48,63
furcal area : Kaprus, Weiner & Pasnik 2016:120,143
furcal field : Pomorski 1996 cited from Babenko & Fjellberg 2015:50
furcal field : Babenko & Fjellberg 2015:48,50,56,57,64,70,71,72
furcal fold : Babenko & Fjellberg 2015:64,71
furcal furrow : Babenko & Fjellberg 2015:71
cuticular furrow : Pomorski 1996 cited from Babenko & Fjellberg 2015:63
cuticular furrow : Babenko & Fjellberg 2015:56,58,63,71
cuticular fold : Babenko & Fjellberg 2015:63,71
furcal reduction : Babenko & Fjellberg 2015:70
furcal remnant : Babenko & Fjellberg 2015:54,56,59,70
furcal rudiment : Babenko & Fjellberg 2015:71
furcal rudiment : cuticular fold Weiner 1996 cited from Babenko & Fjellberg 2015:49;
furcal rudiment : cuticular fold Weiner & Kaprus 2014 cited from Babenko & Fjellberg 2015:49
furcal rudiment : cuticular fold Kaprus, Weiner & Pasnik 2016:123,126,129,131,133,137,139,142
furcal rudiment : cuticular furrow Shvejonkova & Potapov 2011 cited from Babenko & Fjellberg 2015:49
furcal rudiment : cuticular furrow Weiner & Kaprus 2014 cited from Babenko & Fjellberg 2015:49
furcal rudiment : finely granulated area Weiner 1996 cited from Babenko & Fjellberg 2015:49
furcal rudiment : finely granulated area Shvejonkova & Potapov 2011 cited from Babenko & Fjellberg 2015:49
furcal rudiment : finely granulated area Weiner & Kaprus 2014 cited from Babenko & Fjellberg 2015:49
furcal rudiment : small pocket Weiner 1996 cited from Babenko & Fjellberg 2015:49
furcal rudiment : kind of pocket Weiner 1996 cited from Babenko & Fjellberg 2015:49
furcal rudiment : deep pocket Weiner 1996 cited from Babenko & Fjellberg 2015:49
manubrial chaetotaxy : Babenko & Fjellberg 2015:71
manubrial setae : Weiner 1996 cited from Babenko & Fjellberg 2015:49,63
manubrial setae : Shvejonkova & Potapov 2011 cited from Babenko & Fjellberg 2015:49
manubrial field : Weiner 1996 cited from Babenko & Fjellberg 2015:50
manubrial field : Babenko & Fjellberg 2015:54,57,58,59,61,71
manubrial field : Kaprus, Weiner & Pasnik 2016:121,123,124,126,127,129,130,131,134,135,136,137,139,140,142
manubrial rows of setae : Babenko & Fjellberg 2015:63,71
dental microchaetae : Kaprus, Weiner & Pasnik 2016:123,126,129,131,134,136,139,142,143
dental setae : Weiner 1996 cited from Babenko & Fjellberg 2015:49,63
dental setae : Shvejonkova & Potapov 2011 cited from Babenko & Fjellberg 2015:49
dental setae : Weiner & Kaprus 2014 cited from Babenko & Fjellberg 2015:49
dental setae : Babenko & Fjellberg 2015:49,63,71
The term "cuticular fold" or "cuticular furrow" is a misconception
Fig.Op3. Onychiurus prolatus from Europe
Manubrial fold; sagital section
Cuticula (black) lined with epidermal layer (red)
Modified after Gisin, H. 1960 Abb.224 up
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Fig.KWP. Manubrial field in Protaphorura vasilinae
After Kaprus, I., Weiner, W.M. & Pasnik, G. 2016 Fig.57
 |
Given the fold bears so-called "dental microchaetae" (cfr Kaprus & al. 2016),
the fold must be lined internally with epithelium
of which some cells are specialised to produce setae.
A folded extracellular cuticular layer can not produce setae.
Therefore the term "cuticular fold" (or "cuticular furrow")
is an erratic term and should be avoided.
The term "integumentary fold" of Stach (1954) is correct.
In addition, the fold is the 'top of the manubrial iceberg', actually.
This is well illustrated by the diversification of the
cuticular granulation of the 4th abdominal sternum of
Protaphorura vasilinae in which the lines of fine granulation mark the
borders of the ancestral manubrium (Fig.KWP).
The manubrial fold
The chaetotaxy of the manubrial field in Protaphorura vasilinae
(Fig.KWP) (cfr Kaprus & al. 2016:142) :
"4 chaetae present in ma-row,
4 chaetae in ma'-row,
4-5 chaetae in mm''-row,
5-6 chaetae in mm'-row,
4 chaetae in mm-row and
4-5 chaetae in mp-row (in adult specimens) (Fig.56(sic)[should be 57])",
shows
1. that the ancestral manubrium of Protaphorura was quite large,
2. that the ancestral manubrium was inserted
in the posterior half of the 4th abdominal sternum
(which matches with the plesiomorph condition for the furcal area) and
3. that the fold forms the apical part of the ancestral manubrium, actually.
While the generic term "integumentary fold" of Stach (1954) is correct,
and while the setae on the fold are referred to as "dental microchaetae" by
Kaprus & al. (2016),
we consider the specific term "manubrial fold" more appropriate
given the fold is the free apical part of the ancestral manubrium,
while the more basal part of the ancestral manubrium fused with the sternite
on which the furcula was inserted.
The fold is not the fusion of the dental remnants, given
there is no evidence whatsoever of a bipartite origin of the fold.
The manubrial fusion
Fig.Hv. Furca in Hypogastrura variata
Modified after Babenko, A., Efeykin, B. & Bizin, M. 2020 Fig.22
 |
The fusion of the anterior manubrial sclerite with the 4th abdominal sternum
can already be observed in some members with reduced furcula of
the more ancestral Hypogastruridae, such as in H. variata (see Fig.Hv).
The anterior manubrial sclerite (a) is distinctly shorter
than the posterior manubrial sclerite (p),
as a result of the partial fusion of the anterior manubrial sclerite
with the sternite of the fourth abdominal segment.
Complete fusion of the anterior manubrial sclerite
results in orthogonally inserted (papillate) dentes
near to the anterior margin of the 4th sternum
as can be observed in Kalaphorura sp.
We conclude that the manubrial fusion
is a generic mechanism that
occured indepently in several members of Podurormorpha and Entomobryomorpha.
With result : a remnant furca located at the anterior margin of the
4th abdominal sternum.
Tetrodontophorinae sensu D'Haese 2002
Stach (1954:18) already concluded that Tetrodontophora and Homaloproctus
"belong to elements of an ancient fauna,
many members of which were quite extinct".
D'Haese (2002:1148) confirmed the more ancient position
of Tetrodontophorinae in the phylogenetic tree of the Onychiuridae.
But D'Haese also showed that Tetrodontophorinae is paraphyletic.
Tetrodontophorinae Stach 1954:6 (= Tetrodontophora + Homaloproctus)
is diagnosed as:
pseudocelli present;
furcula and pigment well developed;
median shaft of head of maxilla well developed, toothed;
sense organ of third antennal segment with many guarding papillae (more than 5) in 2-3 transversal rows;
body length large 5-7 mm.
Lophognathellinae Stach 1954:6 (= Lophognathella)
is diagnosed as:
pseudocelli present;
furcula and pigment well developed;
median shaft of head of maxilla absent;
sense organ of third antennal segment with few (4) guarding papillae in one row;
body length small 1.5 mm.
Tetrodontophorinae D'Haese 2002:1148 = Homaloproctus + Lophognathella + Tetrodontophora
Fig.DH. Cladogram of Onychiuridae
Modified after D'Haese, C. 2002 Fig.1
 |
The molecular phylogeny of D'Haese,
showed that
Tetrodontophorinae (= Homaloproctus + Lophognathella + Tetrodontophora),
with a well developed furcula, which is the plesiomorph ancestral condition,
are a paraphyletic artificial assemblage of ancient species,
which are embedded in the Onychiurinae (Fig.DH).
The paraphyletic Tetrodontophorinae and the monophyletic Onychiurinae s.s.
form together the monophyletic Onychiurinae.
Homaloproctus (sensu Stach 1954:6,10) is diagnosed as :
abd.6 delimited distinctly from abd.5, very narrow;
abd.6 with rounded posterior margin;
antennal basis with 1 pseudocellus;
ant.4 with 6 small apical papillae;
median shaft of head of maxilla well developed, toothed;
sense organ of third antennal segment with many guarding papillae (more than 5)
in 2-3 transversal rows;
body length large 5-7 mm.
Lophognathella (sensu Stach 1954:6) is diagnosed as:
median shaft of head of maxilla absent;
sense organ of third antennal segment with few guarding papillae (4) in one row;
body length small 1.5 mm.
Tetrodontophora (sensu Stach 1954:6,9,10,PlateI) is diagnosed as :
abd.6 ankylosed with abd.5 in median part of dorsum without suture (Pl.I Fig.8);
abd.6 lateral corners protrude backwards in shape of small triangular processes (Pl.I Fig.8);
antennal basis with 3 pseudocelli;
ant.4 without apical papillae;
median shaft of head of maxilla well developed, toothed;
sense organ of third antennal segment with many guarding papillae (12-17)
in 2-3 transversal rows (Pl.I Fig.1);
body length large 5-7 mm.
The rise and fall of the furcula in Onychiuridae
An alternative approach to Onychiuridae.
Based on the molecular phylogeny of D'Haese (2002:1148,Fig.1),
we define the following taxonomic hierarchy for Onychiuridae (Fig.DH) :
Onychiuridae = Protaphorurinae + Onychiurinae
Protaphorurinae = Protaphorurini + Supraphorura MDm
Protaphorurini = Protaphorura M-- + Yoshiiphorura M-- + Jacekaphorura M-- + Spelaphorura ??? + Megaphorura ???
Onychiurinae = Tetrodontophorinae + Onychiurinae s.s. M/-D/--
Onychiurinae = Homaloproctus MDm + (Lophognathella MDm + (Tetrodontophora MDm + Onychiurinae s.s. M/-D/--))
Onychiurinae = Homaloproctus MDm + Lophonychiuroforma M/-D/-m/-
Lophonychiuroforma = Lophognathella MDm + Tetronychiuroforma M/-D/-m/-
Tetronychiuroforma = Tetrodontophora MDm + Onychiurinae s.s. M/-D/--
Furcal formula: M:manubrium present, D:dentes present, m:mucrones present, -:absent, /:or, ?:to be done
In the apomorph sistergroup of the Onychiurinae, the Protaphorurinae,
the ancestral furcula has been reduced.
In the plesiomorph group of the Protaphoruninae, the Protaphorurini,
the furcal insertion is located at the posterior part of the sternum,
the dentes and mucrones are lost,
and the manubrium is fused with the sternum,
except for a small apical integumentary fold,
the manubrial fold, bearing 2(+2) setae.
In the apomorph group of the Protaphoruninae, Supraphorura,
the furcal insertion is at the anterior part of the sternum,
the manubrium, dentes and mucrones are still present,
but in a much simplified form.
A manubrial fold is also present in some members of Onychiurinae s.s.,
but that fold is homoplastic to the manubrial fold of Protaphorurini.
We define tentatively the following monophyletic groupings in Onychiurinae :
Onychiurinae = Homaloproctus + ((Lophognathella + Ussuriaphorura) + ((Tetrodontophora + Anodontohorus) + Onychiurinae s.s.))
Onychiurinae = Homaloproctus + Lophonychiuroforma
Lophonychiuroforma = Lophognathellinae + (Tetrodontophorinae + Onychiurinae s.s.)
Lophonychiuroforma = Lophognathellinae + Tetronychiuroforma
Tetronychiuroforma = Tetrodontophorinae + Onychiurinae s.s.
Tetrodontophorinae = Tetrodontophora + Anodontophorus
Lophognathellinae = Lophognathella + Ussuriaphorura
Differential diagnoses :
Protaphorurinae
PAO with simple vesicles that are placed radially to
the longitudinal axis of the PAO.
Onychiurinae
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO.
Homaloproctus
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO;
with 6 small papillae on the antenna tip; and
with a group of clubbed setae distally on the dorsal side of the tibiotarsus
(Pomorski 2007:63).
Lophonychiuroforma
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO;
without 6 small papillae on the antenna tip, and
without tibiotarsal clubbed setae.
Lophognathellinae
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO;
without 6 small papillae on the antenna tip,
without tibiotarsal clubbed setae, and
the median shaft of the head of the maxilla absent.
Tetronychiuroforma
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO;
without 6 small papillae on the antenna tip,
without tibiotarsal clubbed setae, and
the median shaft of the head of the maxilla present.
Tetrodontophorinae
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO;
without 6 small papillae on the antenna tip,
without tibiotarsal clubbed setae,
the median shaft of the head of the maxilla present,
the furcula not reduced, and
pigment present.
Onychiurinae s.s.
PAO not with simple vesicles that are placed radially to
the longitudinal axis of the PAO;
without 6 small papillae on the antenna tip,
without tibiotarsal clubbed setae,
the median shaft of the head of the maxilla present,
the furcula reduced, and
pigment reduced.
In the Onychiuridae, the furcula has been reduced at least 2 times, independent
from eachother : at first in Protaphorurinae,
and later again in Onychiurinae s.s.
Reduction scheme of furcula
Fig.F1. Tetrodondophora bielanensis from Czechia
Furcal area; ventral view
Modified after Deml, M. 2008.04.21
 |
As model for the ancestral furcula of Onychiurinae we selected the furcula
of Tetrodontophora bielansensis which is one of the more ancestral forms
of Onychiurinae s.l. (Fig.F1) with complete well developed furcal configuration :
basal manubrium (m), 2 dentes (d), each with mucro (mu); and retinaculum (r)
present.
Fig.F2. Supraphorura
Furcal area; ventral view
Modified after Deml, M. 2008.04.21
 |
A first type of reduction of the furcula (Fig.F2) :
1. the large basal part of the manubrium is fused with the sternum, only
a small apical part (m) remained
2. the dentes (d) are reduced in length and fused with the remnant manubrium
3. the mucrones (mu) are reduced in size
4. the retinaculum (r) is still present.
This type of remnant furcula is typical for the extant Supraphorura.
Due to the fusion of the large basal part of the manubrium,
the remnant furcula
is situated at the anterior margin of abd.4,
and the furcal area apparently is displaced to the anterior margin of the
sternum.
Fig.F2. Protaphorura
Furcal area; ventral view
Modified after Deml, M. 2008.04.21
 |
Another type of reduction of the furcula (Fig.F2) :
1. the large basal part of the manubrium is fused with the sternum, only
a small apical part (m) remained (the manubrial fold)
2. the dentes (and mucrones) are lost
3. the retinaculum is lost.
This type of remnant furcula is typical for the extant Protaphorura
and many Onychiurinae s.s.
Due to the fusion of the large basal part of the manubrium,
the remnant furcula
is situated at the anterior margin of abd.4,
and the furcal area apparently is displaced to the anterior margin of the
sternum.
Fig.F3. Kalaphorura
Furcal area; ventral view
Modified after Deml, M. 2008.04.21
 |
Another type of reduction of the furcula (Fig.F3) :
1. the manubrium is completely fused with the sternum of abd.4
2. the dentes (d) are each fused with the sternum of abd.4
and are reduced in shape to demispherical warts
3. the mucrones are completely lost
4. the retinaculum is (r) reduced : the corpus is lost, the 2 rami
each fused with the sternum of abd.3
and are reduced in shape to small demispherical warts.
This type of remnant furcula is typical for the extant Kalaphorura
and Psyllaphorura.
Due to the complete fusion of the manubrium, the remnant furcula
is situated at the anterior margin of abd.4,
and the furcal area apparently is displaced to the anterior margin of the
sternum.
Fig.F4. Onychiurus
Furcal area; ventral view
Modified after Deml, M. 2008.04.21
 |
Another type of reduction of the furcula (Fig.F4) :
1. the manubrium is completely fused with the sternum of abd.4
2. the dentes (d) are each fused with the sternum of abd.4
and are reduced completely to area's with fine granulation
3. the mucrones are completely lost
4. the retinaculum is completely reduced.
This type of remnant furcula is typical for the extant Onychiurus.
Due to the fusion of the large basal part of the manubrium,
the remnant furcula
is situated at the anterior margin of abd.4,
and the furcal area apparently is displaced to the anterior margin of the
sternum.
Case examples
Reduced furcula as manubrial papilla with dentes and mucrones and retinaculum
Furcal area located at anterior margin of fourth abdominal sternum :
To be completed.
Remnant furcula as dental papillae and retinaculum
Furcal area located at anterior margin of fourth abdominal sternum :
To be completed.
Remnant furcula as area with fine granulation
Furcal area located at anterior half of fourth abdominal sternum :
Fig.Te. Thalassaphorura encarpata ♀ from Poland
Furcal area; ventral view
Modified after Pomorski, R.J. 1998 Fig.362
 |
Fig.Te2. Thalassaphorura encarpata ♀ from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.367
 |
Thalassaphorura encarpata
Onychiurus ambulans
Fig.Oa. Onychiurus ambulans ♂ from Poland
Furcal area; ventral view
Modified after Pomorski, R.J. 1998 Fig.417
 |
Fig.Oa2. Onychiurus ambulans ♂ from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.421
 |
Fig.Oa3. Onychiurus ambulans from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.45
 |
Fig.Ow. Oligahorura wanglangensis ♂ from China
Furcal area; ventral view
Modified after Sun, X. et al. Fig.7
 |
Oligaphorura wanglangensis
Fig.Jf2. Jacekaphorura catherinae from North-East Russia
Furcal area; ventral view
Modified after Babenko, A. 2013 Fig.5
 |
Jacekaphorura catherinae
Furcal area translocated to half of fourth abdominal sternum :
In front of the furcal area are some transverse rows of setae.
Fig.Hc. Hymenaphorura creatricis ♂ from Poland
Furcal area; ventral view
Modified after Pomorski, R.J. 1998 Fig.89
 |
Fig.Hc. Hymenaphorura creatricis ♂ from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.95
 |
Hymenaphorura creatricis
Fig.Hi. Heteraphorura iranica ♂ from Iran
Furcal area; ventral view
Modified after Kaprus, I. & al. 2017 Fig.8
 |
Heteraphorura iranica
To be completed.
Remnant furcula as unpaired fold
Furcal area located at anterior half of fourth abdominal sternum :
Fig.Pa. Protaphorura armata ♀ from Poland
Furcal area; ventral view
Modified after Pomorski, R.J. 1998 Fig.272
 |
Fig.Pa2. Protaphorura armata ♀ from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.276
 |
Protaphorura armata
Protaphorura campata
Fig.Pc. Protaphorura campata ♀ from Poland
Furcal area; ventral view
Modified after Pomorski, R.J. 1998 Fig.320
 |
Fig.Pc2. Protaphorura campata ♀ from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.326
 |
Fig.Pc3. Protaphorura campata from Poland
Remnant furcula; ventral view
Modified after Pomorski, R.J. 1998 Fig.43
 |
Fig.Pg. Protaphorura golestanica ♂ from Iran
Furcal area; ventral view
After Kaprus, I. & al. 2017 Fig.15
 |
Protaphorura golestanica
Fig.Ok. Oligahorura kedroviensis ♀ from Far East Russia
Furcal area; ventral view
Modified after Sun, X. et al. 2019 Fig.21
 |
Oligaphorura kedroviensis
Fig.Ou. Oligahorura ussurica ♀ from Far East Russia
Furcal area; ventral view
Modified after Sun, X. et al. Fig.17
 |
Oligaphorura ussurica
Fig.Jf. Jacekaphorura furcata from North-East Russia
Furcal area; ventral view
Modified after Babenko, A. 2013 Fig.9
 |
Jacekaphorura furcata
Furcal area translocated to half of fourth abdominal sternum :
To be completed.
Tentative phylogenetic relationships
Fig.Tree. Tentative phylogenetic relationships
+------------ Supraphorura
+-+
| +------------ Protaphorurini
<-On-+
+-+------------ Homaloproctus
|
+-+---------- Lophognathellinae
|
+-+-------- Tetrodontophorinae s.s.
|
| +------ Oligaphorurini
| |
+-+ +---- Kalaphorura + Psyllaphorura?
| |
+-+ +-- Hymenaphorurini?
+-+
+-- Onychiurini + Thalassaphorurini
|
Based on the evolutionary state of the furcula,
a tentative phylogenetic tree of the Onychiuridae can be constructed (Fig.Tree).
The evolutionary axis is from most developed furcula (plesiomorph condition)
to most reduced furcula (apomorph condition).
To be completed.
Conclusion
To be completed.
Acknowledgements
We would like to thank, in alphabetical order,
Miroslav Deml,
Gertjan Kamsteeg
and
Jérôme Picard,
for the use as illustrations of their respective photographs.
References
