Protoxenidae fam. nov. (Insecta, Strepsiptera) from Baltic
amber — a ‘missing link’ in strepsipteran phylogeny
Blackwell Publishing, Ltd.
HANS POHL, ROLF G. BEUTEL & RAGNAR KINZELBACH
Accepted: 15 March 2004
Pohl, H., Beutel, R. G. & Kinzelbach, R. (2005). Protoxenidae fam. nov. ( Insecta, Strepsiptera) from Baltic amber — a ‘missing link’ in strepsipteran phylogeny. — Zoologica Scripta,
34, 57– 69.
A male specimen of a new strepsipteran genus and species (Protoxenos janzeni gen. et sp. nov.)
and family (Protoxenidae fam. nov.) found in Baltic amber is described and illustrated. It shows
features which are apparently more plesiomorphic than in hitherto known strepsipterans, such
as laterally inserted eight-segmented antennae, very robust mandibles with a broad base, a
prominent galea, a comparatively short, transverse metapostnotum, hindwings that are feebly
extended in a rostrocaudal direction, and equally sclerotized abdominal tergites and sternites.
Based on a cladistic analysis of 46 characters of males of 11 genera and three outgroup taxa,
P. janzeni is the sister group of all other known strepsipterans, and Mengea the sister group of
Strepsiptera s.s. Eoxenos is the sister group of the remaining extant strepsipterans and Mengenillidae is therefore paraphyletic. Newly established groundplan features of Strepsiptera will
facilitate the clarification of the systematic position of the Order in future studies.
Hans Pohl & Ragnar Kinzelbach, Institut für Biodiversitätsforschung, Allgemeine und Spezielle
Zoologie, Universitätsplatz 2, D-18055 Rostock, Germany. E-mail: [email protected]
Rolf G. Beutel, Institut für Spezielle Zoologie und Evolutionsbiologie, FSU Jena, Germany
Introduction
The discovery of the single known specimen of Protoxenos
janzeni gen. et sp. nov. at a fossil fair in Hamburg is a highlight in the history of strepsipteran studies. The group is
poorly represented in the fossil record. The creation of
Protoxenidae fam. nov. helps reduce the ‘morphological gap’
between the twisted winged parasites and the other endopterygote insects. The numerous autapomorphies of the
endopterygote Strepsiptera remain the primary cause of the
difficulties involved with the Order’s systematic placement.
Despite intensive efforts, its phylogenetic position is still
controversial.
World-wide, there are c. 600 extant described strepsipteran
species, traditionally classified within nine or 10 families
( Kinzelbach 1978, 1990; Pohl 2002). The second instar
larvae of all species and the neotenic females of the Stylopidia
are endoparasites of various higher taxa of insects including
the Zygentoma, Blattaria, Mantodea, Orthoptera, Hemiptera,
Hymenoptera and Diptera. In correlation with their parasitic
life-style, they have evolved an extremely modified morphology and unusual life histories. Conspicuous characters of the
males include reduced forewings, which resemble halteres
and function in a similar manner, fan-shaped hindwings,
and ‘raspberry’ compound eyes. Females are always wingless.
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
They are free living in Mengenillidae and partly leave the larval exuviae. Stylopid females extrude from their host’s body
wall only with the anterior part of their body; they remain
enclosed in the exuviae and form a functional unit with
them within the host. Kinzelbach (1971a,b, 1978, 1990) and
Kathirithamby (1989) have provided comprehensive reviews
of the biology, morphology and systematics of the Strepsiptera.
Nearly all records of fossil Strepsiptera are of free-living
males found in Baltic or Dominican amber, which were likely
trapped on the sticky surface of fresh resin ( Table 1). There are
a few exceptions: one primary larva of Stichotrema eocaenicum
( Haupt, 1950) (Myrmecolacidae) found in Eocene brown coal
of the Geiseltal near Halle an der Saale (Kinzelbach & Lutz
1985), a stylopized Camponotus sp. (Hymenoptera: Formicidae)
with two male puparia of Myrmecolacidae, found in Middle
Eocene Messel oil slate (Lutz 1990), and one female of a purported
species of Myrmecolacidae parasitizing a prionomyrmecine
ant, found in Baltic amber ( Pohl & Kinzelbach 2001).
Most of the fossils found so far are closely related (or nearly
identical) to representatives of extant genera or species, in
particular those extracted from Dominican amber ( Kathirithamby & Grimaldi 1993; Kinzelbach & Pohl 1994; Pohl &
Kinzelbach 1995). Even though Eocene brown coal (45–50
million years old), Baltic (39–50 Myo) and Dominican amber
57
Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber • H. Pohl et al.
Table 1 List of fossil Strepsiptera.
Taxa
Locality and stratum
Stadium
Host
Protoxenidae fam. nov.
Protoxenos janzeni gen. et sp. nov.
Baltic amber, Eocene, c. 39–50 Myo
male
unknown
Mengeidae Pierce, 1908
Mengea teriaria (Menge, 1866)
M. mengei Kulicka, 1979
Baltic amber, Eocene
Baltic amber, Eocene
male
male
unknown
unknown
Bohartillidae Kinzelbach, 1969
Bohartilla joachimscheveni Kinzelbach & Pohl, 1994
B. megalognatha (partim) (Pohl & Kinzelbach, 1995)
B. kinzelbachi Kathirithamby & Grimaldi, 1993
Dominican amber, Oligo-Miocene, c. 25–30 Myo
Dominican amber, Oligo-Miocene
Dominican amber, Oligo-Miocene
male
unknown
male
unknown
Elenchidae Perkins, 1905
Protelencholax schleei Kinzelbach, 1979
Dominican amber, Oligo-Miocene
male
unknown
Dominican amber, Oligo-Miocene
Dominican amber, Oligo-Miocene
Dominican amber, Oligo-Miocene
Baltic amber, Eocene
Baltic amber, Eocene
Baltic amber, Eocene
Dominican amber, Oligo-Miocene
Dominican amber, Oligo-Miocene
Brown coal of the Geiseltal near Halle (Saale,
Germany), Eocene, c. 45–50 Myo
Baltic amber, Eocene
Baltic amber, Eocene
Messel oil slate near Darmstadt,
Germany, Eocene c. 50 Myo
male
male
male
male
male
male
male
male
first instar
unknown
unknown
unknown
unknown
unknown
unknown
unknown
unknown
unknown
male
male
male
puparia
Baltic amber, Eocene
female
unknown
unknown
Camponotus sp.
(Formicidae:
Formicinae)
Prionomyrmex sp.
(Formicidae:
Prionomyrmecinae)
Baltic amber, Eocene
male
Myrmecolacidae Saunders, 1872
Caenocholax brodzinskyi Kathirithamby & Grimaldi, 1993
C. dominicensis Kathirithamby & Grimaldi, 1993
Myrmecolax glaesi Kinzelbach, 1983
Palaeomyrmecolax giecewiczi Kulicka, 2001
P. gracilis Kulicka, 2001
P. succineus Kulicka, 2001
Stichotrema beckeri de Oliveira & Kogan, 1959
S. dominicanum Kinzelbach & Pohl, 1994
S. eocaenicum (Haupt, 1950)
S. triangulum Pohl & Kinzelbach, 1995
S. weitschati Kinzelbach & Pohl, 1994
S. sp. (Lutz, 1990; Kinzelbach & Pohl, 1994)
Genus and species unknown,
tentatively placed in the Myrmecolacidae
(Pohl & Kinzelbach, 2001)
Stylopidae Kirby, 1813
Jantarostylops kinzelbachi Kulicka, 2001
(c. 25 Myo) are comparatively recent within the context of the
full extent of the insect fossil record, the fossils do contribute
to our understanding of the phylogeny and evolution of
Strepsiptera. The Mengeidae, represented by two extinct
species, Mengea tertiaria (Menge, 1866) and M. mengei
Kulicka, 1979, both found in Eocene Baltic amber, possess a
free labrum and a closed cell of the hindwing as important
plesiomorphic character states. Therefore, Mengeidae could
be referred to as the most basal taxon and the group with the
most preserved plesiomorphic features within the Order.
The age and early evolution of Strepsiptera are not well
documented by fossil evidence. No Mesozoic or Palaeozoic
specimens are known at present ( Table 1). However, the
available fossils do permit estimation of the approximate time
frame within which evolutionary events may have occurred.
The purported female myrmecolacid mentioned above ( Middle Eocene) strongly suggests that the dual host relationship
that characterizes extant representatives of this family may
58
unknown
have evolved at a later stage of the evolution of the group. Today,
each sex parasitizes representatives of different higher taxa of
insects: males develop in Formicidae (Hymenoptera), whereas
females parasitize either Mantodea or Ensifera. The primary
hosts of Myrmecolacidae were certainly ants and the switching
of the female hosts took probably place during the radiation
of ants 40–50 million years ago (Grimaldi et al. 1997).
Furthermore, the presence in Tertiary deposits of strepsipterans apparently very closely related to extant taxa
provides additional evidence of the considerable age of the
group. As specialized taxa like the Myrmecolacidae existed
already in the Eocene, it is likely that the more basal branching events occurred much earlier, probably in the Permian
(Kinzelbach 1990). This view is strongly supported by the
presence of Diptera and Coleoptera in Permian deposits
(Labandeira 1994). Both groups are considered as potential
sister groups of Strepsiptera in recent studies (Whiting et al.
1997; Wheeler et al. 2001; Beutel & Gorb 2001).
Zoologica Scripta, 34, 1, January 2005, pp57– 69 • © The Norwegian Academy of Science and Letters
H. Pohl et al. • Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber
The fossils known today do not contribute much to the
solution of the phylogenetic placement of the Order — what
has been termed the ‘Strepsiptera problem’ (Kristensen 1981,
1999). However, the new fossil male found in Baltic amber
that we describe here enables us to add further characters to
the groundplan, and to recognize features formerly considered as possible synapomorphies with other groups as character states which were not present in the common ancestor
of Strepsiptera s.l. In addition, evaluation of the morphology
of P. janzeni gen. et sp. nov. provides an improved database
for an analysis of the basal splitting events within the group.
Materials and methods
We were loaned the only known specimen of P. janzeni by
J.-W. Janzen (Seevetal, Germany), who purchased it at a fossil
fair in Hamburg. It has since been acquired by Zoologische
Abteilung, Hessisches Landesmuseum Darmstadt (Germany).
Additional species examined (males)
Mengeidae. Mengea tertiaria (Menge, 1866 ) (specimens
embedded in Baltic amber)
Mengenillidae. Eoxenos laboulbenei de Peyerimhoff, 1919 ( Italy)
(SEM ), Mengenilla chobauti Hofeneder, 1910 ( Italy) (SEM),
Mengenilla sp. (undescribed species from Tunisia) (90% ethanol; diss. = dissected; micr. = microtome sections; SEM),
Mengenilla sp. (Australian species; ANIC, CSIRO Canberra)
(70% ethanol; micr. = microtome sections; SEM)
Elenchidae. Elenchus tenuicornis (Kirby, 1811) (SEM)
Corioxenidae. Dundoxenos kinzelbachi Luna de Carvalho, 1985
(Yemen) (SEM), Malayaxenos trapezonoti Pohl & Melber, 1996
(Germany) (SEM)
Halictophagidae. Halictophagus agalliae Abdul-Nour, 1970 (Germany) (SEM), H. sp. (undescribed species from Yemen) (SEM)
Myrmecolacidae. Stichotrema sp. ( N. Sumatra) (SEM)
Xenidae. Xenos vesparum Rossius, 1793 (Germany) (Bouin;
diss., micr., SEM)
Stylopidae. Stylops melittae (Germany) (FAE = ethanolformaldehyde-acetic acid; micr., SEM)
Protoxenos janzeni and Mengea tertiaria specimens were
examined using a Zeiss Stemi SV 11 stereo microscope and
camera lucida equipment and a Zeiss Photomikroskop II at
various magnifications, up to 100×. A drop of glycerine and a
coverslip was placed over the specimens to avoid distortions
on the slightly arched surface of the amber. Photographs
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
were made with a Wild Leitz MPS 52 camera mounted on a
Wild Makroskop M 420. The remaining specimens were
dehydrated in ethanol, critical-point dried, mounted on
holders and sputter-coated with gold. They were examined
using a Zeiss DSM 960 A at 10–20 kV.
Cladistic analysis was performed using PAUP v. 4.0b10
(Swofford 2002) (branch and bound search). Analyses were
carried out with all 15 multistate characters unordered and
with six characters ordered (all characters with equal weight
in all analyses). A rationale for using 7, 22, 29, 33, 38 and 46
as ordered is presented below (Appendix 1, list of characters).
This appears not to be justified in the case of the other multistate characters, as apomorphic states may have evolved
independently from the presumptive groundplan condition
of Strepsiptera and not necessarily via an intermediate state
(e.g. loss of more than one tarsomere or antennomere).
Representatives of Coleoptera (Priacma serrata LeConte,
Cupedidae), Megaloptera (Sialis lutaria Linnaeus, Sialidae)
and Diptera (Tipula sp., Tipulidae) were used as outgroups.
Bremer support was calculated using the strict consensus
approach. Analysis of character evolution was conducted in
MACCLADE 4.0 (Maddison & Maddison 2000).
The list of characters used in the analysis is provided in
Appendix 1, the character state matrix in Table 2.
Systematics
Protoxenidae fam. nov.
Description. Male. Body compact, length more than 7 mm.
Head capsule heavily sclerotized. Coronal suture well developed.
Clypeus transverse and distinctly separated from frons by
epistomal suture. Ocelli absent. Ommatidia of compound eyes
distinctly separated by chitinous bars densely covered with
microtrichia. Labrum prominent and free, with two anteriorly directed processes. Antennae eight-segmented, inserted
laterally, close to anterior margin of eyes. Mandibles robust,
with broad base. Maxilla without recognizable cardo. Mesal
lobe present proximal to one-segmented palp. Sensorial pit
present on lateral side of palpomere. Pro- and mesothorax
short and closely connected (in general structure very similar
to the pro- and mesothorax of the Mengenillidae). Anterior
margin of prothorax straight. Anterior margin of mesothorax
weakly concave. Mesothoracic wings club-shaped and transformed into halteres. Metascutum protruding, semicircular.
Scutellum triangular, with straight posterior margin. Postlumbium very small, slot-like. Metapostnotum plate-like, about
as long as broad, shorter than alinotum. Metacoxae not fully
integrated into metathoracic sclerites and not fused medially.
Legs slender, with 5-segmented tarsi with a pair of strong claws.
All tarsal segments cylindrical and without specialized adhesive
hairs. Hind wings slightly longer than wide, without transverse
veins and closed cells. Abdominal tergites and sternites equally
sclerotized. Tergites II–VII broad, rectangular. Tergite VIII longer
59
Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber • H. Pohl et al.
Table 2 Character state matrix; (?) refer to missing data (—) to inapplicable characters. Characters 7, 22, 29, 33, 38, 46 were treated as ordered
in the second analysis.
Sialis
Tipula
Priacma
Protoxenos
Mengea
Eoxenos
Mengenilla
Mengenilla austr
Dundoxenos
Malayaxenos
Elenchus
Halictophagus
Xenos
Stichotrema
Stylops
Sialis
Tipula
Priacma
Protoxenos
Mengea
Eoxenos
Mengenilla
Mengenilla austr
Dundoxenos
Malayaxenos
Elenchus
Halictophagus
Xenos
Stichotrema
Stylops
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
0
0
0
1
2
2
2
2
2
2
2
2
2
2
2
0
0
0
?
?
1
1
1
1
1
1
1
1
1
1
1
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
0
0
1
0
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
2
2
1
2
2
2
2
2
2
2
0
0
0
1
0
—
—
0
—
—
—
—
—
—
—
0
1
0
0
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
2
2
2
2
2
2
2
2
2
2
2
0
0
0
0
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
0
1
0
1
0
0
0
0
0
0
0
0
1
0
0
0
1
0
0
0
0
0
0
0
1
1
1
1
1
1
0
1
0
0&1
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
1
1
1
1
1
1
0
1
0
0
0
0
0
0
1
0
0
1
1
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
1
0
0
0
0
0
0
1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
?
1
1
1
1
1
1
1
1
1
1
1
0
1
0
0
0
0
0
0
2
2
0
1
0
0
0
0
—
0
0
0
1
2
2
—
—
2
2
2
2
2
0
1
0
0
1
1
1
1
1
1
1
1
1
1
1
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
1
1
0
0
0
0
0
0
0
0
0
0
0
0
?
1
1
1
1
1
1
1
1
1
1
1
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
—
0
1
2
2
2
2
2
2
2
2
2
2
2
0
—
0
1
1
1
1
1
1
1
1
1
1
1
1
0
—
0
2
1
2
2
2
2
2
2
2
2
2
2
1
1
1
0
0
0
0
0
1
1
1
1
1
1
1
0
0
0
1
2
2
2
2
2
2
2
2
2
2
2
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
0
1
3
2
1
1
1
0
0
0
0
0
0
0
0
1
2
2
2
2
2
2
1
0
1
0
0
0
0
0
1
1
2
2
3
3
3
2
0
2
0
0
0
0
0
1
1
2
2
2
2
2
0
0
0
0
0
0
0
0
1
1
2
0
2
2
2
1
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
0
—
?
0
0
0
0
0
1
1
0
0
0
0
0
0
—
2
?
0
0
0
0
0
0
0
1
1
1
1
0
0
1
0
1
1
1
1
1
1
1
1
1
1
1
0
0&1
0
1
?
1
1
1
2
2
2
2
2
2
2
and narrower than the previous tergites. Shape of sternites
II–VIII very similar to corresponding tergites. Segment IX
short and ring-shaped, with the caudally elongated subgenital
plate bearing the aedeagus. Spiracles present on pleurites
I–VII. Segment X long and cylindrical, reaching beyond the
tip of segment IX.
Females. Larvae and hosts. Unknown.
plate-like metapostnotum which is about as long as broad,
and hindwings slightly longer than wide.
Protoxenos gen. nov.
Description. Male. Antennae eight-segmented with flabellum
on segments III–VII. Processes of labrum reaching almost
the tips of the mandibles. Sensorial pit on maxillary palps of
elongate ovoid shape. Hindwings with two detached veins R2
and R3 and three detached veins MA1 to MA3.
Type genus. Protoxenos gen. nov.
Type species. Protoxenos janzeni sp. nov.
Etymology. Protos (first) and xenos (stranger, guest), both Greek,
referring to the plesiomorphic status of the new taxon and the
genus Xenos, the first strepsipteran genus to be described by
Rossius in 1793.
Diagnosis. Differs from all other known Strepsiptera by the
following set of characters: large body size, eight-segmented
antenna, free and prominent labrum with two processes,
60
Protoxenos janzeni sp. nov. (Figs 1A– E, 2A– D, 3A)
Fossil Material. Holotype male: HLMD-Strep-11-HT (Hessisches Landesmuseum Darmstadt, Department of Zoology)
is the only inclusion in a medium yellow, rectangular piece of
amber (46 × 27 × 7 mm). The fossil lies with its left lateral
side very close to the surface of the amber.
Zoologica Scripta, 34, 1, January 2005, pp57– 69 • © The Norwegian Academy of Science and Letters
H. Pohl et al. • Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber
Fig. 1 A–E. Protoxenos janzeni gen. et sp. nov., in Baltic amber. —A. Habitus, dorsal view. —B. Habitus, ventral view. —C. Head, pro-, meso-,
and apical part of metathorax, dorsal view. —D. Head, ventral view. —E. Habitus, lateral view.
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
61
Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber • H. Pohl et al.
Fig. 2 A–D. Protoxenos janzeni gen. et sp. nov. —A. Habitus, dorsal view. —B. Head, dorsal view. —C. Head, ventral view. —D. Head, lateral view.
Scale bars = 1 mm (A); 0.5 mm (B, C, D). Abbreviations: Clp, clypeus; Cs, coronal suture; es, epistomal suture; fw, fore wing; Ga, galea; Lm, labrum;
Md, mandible; Mx, maxilla; PMx, maxillary palp; PN, postnotum of metathorax; PoL, postlumbium; sg, sensory pit; X, tenth abdominal segment.
Description. Most of left wing and tarsal segments 2–5 of the
left foreleg lost on the surface of the amber due to polishing.
Part of head, thorax and ventral parts of the abdomen covered
with whitish impurities.
Approximate total length 7.6 mm; width of head ≈ 1.3 mm;
approximate length of antenna 0.8 mm; length of forewing
1.3 mm; radial length of hindwing 5.1 mm; length of metathorax 2.4 mm; colour: body reddish brown with brighter
62
intersegmental membranes. Whole body, except for mandibles
covered with microtrichia.
Head orthognathous, transverse and heavily sclerotized,
with coronal suture abutting frontal margin of compound
eyes in dorsal view. Posterior margin of head with dorsal,
moderately deep, V-shaped emargination. Compound eyes oval
in lateral aspect, each with approximately 110 ± 10 ommatidia.
Antennae short, eight-segmented, approximately 0.6 × as wide
Zoologica Scripta, 34, 1, January 2005, pp57– 69 • © The Norwegian Academy of Science and Letters
H. Pohl et al. • Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber
Fig. 3 A, B. Hindwings of Protoxenos and Mengea. —A. Protoxenos janzeni gen. et sp. nov. —B. Mengea tertiaria (modified from Kinzelbach 1978).
Abbreviations: C, costa; Sc, subcosta; R1–5, radius; MA1–3, media anterior; CuA1–2, cubitus anterior; CuP, cubitus posterior.
as maximum width of head. Segments III−VII with flattened
flabella of almost equal length. Scapus short, 2/3 as long as
pedicellus. Antennal segments III−VIII short and of almost
equal length. Sensorial organ on segment 4 (Hofeneder’s
organ) not visible. Segment VIII long, reaching almost the
tip of the flabellum of segment VII. Few setae at an indentation in the middle of segment VIII, probably marking the
tip of the antennal segment. Flabella densely covered with
sensilla. Labrum free, slightly longer than maxillae without
palp, with long processes enclosing a deep median emargination. Mandibles gradually narrowing towards rounded apex,
slightly intercrossing distally. Mesal surface not visible. Proximal part of maxillae about 2.5× as long as broad, slightly
widening distally. Mesal process about 0.6× as long as maxillary palp, rounded apically. Palp club-shaped, somewhat
longer than stipital part of maxilla; laterally with a long, slotlike sensorial pit. Mouth opening and other ventral structures
of the head not discernible due to impurities.
Ratio of alinotum /postnotum 1.7 : 1. Hind margin of
postnotum weakly convex. Measurement of mesothoracic
width not possible due to turbidity. Most part of right hindwing extended. Venation with C, Sc, R1−4, MA1−3, CuA1
and 2. Veins R2, R3, MA1−3 detached. Possibly existing additional cubital veins not visible due to a fold in the cubital area.
Aedeagus covered by artefacts, not clearly visible.
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
Etymology. Named after Jens-Wilhelm Janzen, Seevetal,
Germany, who purchased the specimen and made it available
for scientific study.
Results of the cladistic analysis
The initial analysis of 43 characters (unweighted and unordered, uninformative characters excluded (chars. 8, 11, 19) of
12 ingroup and three outgroup taxa resulted in 15 minimal
length trees with 82 steps (CI = 0.7561; HI = 0.2683, RC =
0.6199) (Fig. 4: strict consensus tree).
Characters 7, 22, 29, 33, 38, and 46 were treated as ordered
in the second analysis (rationale see above). The uninformative
characters were excluded. We obtained six minimal length
trees with 84 steps (CI = 0.7381; HI = 0.2857, RC = 0.6160)
( Fig. 5: preferred tree). Only characters 22 and 38 changed
their position on the topology. In contrast to the results of the
first analysis, the monophyly of Stylopidia excluding Corioxenidae (= Stylopiformia) was confirmed in all trees. This
clade is strongly supported by a unique female apomorphy,
the presence of a fissure-shaped birth opening on the ventral
side of the cepalothorax. The Corioxenidae release the first
instar larvae through the mouth opening.
The preferred tree with a sister-group relationship between
Elenchus on one hand and the genera Stichotrema, Xenos and
Stylops on the other was chosen, as the monophyletic origin
63
Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber • H. Pohl et al.
Strepsiptera s.s. (excl. stem-lineage) (bs 4). Labrum absent (7.2),
fusion of antennomeres 6 and 7 (14.1, CI 0.5), mandibular base
broad, but without anterior articulation (secondary mandibular
joint) (22.1)
Strepsiptera s.s. (excl. Eoxenos) (bs 2). Mandibular base narrowed,
separated from head capsule by membranous area (22.2), sensorial groove of maxillary palp absent (26.0, CI = 0.5)
Mengenilla. Antennomere 5 flabellate (17.1)
Stylopidia = Strepsiptera s.s. excl. Mengenillidae ( bs 4). Scutopraescutal region not strongly arched (32.1, CI 0.5), claws
absent (36.2), adhesive hairs present on 4th tarsomere (38.1,
CI 0.5), spiracles II−VII reduced (46.2)
Stylopiformia = Strepsiptera s.s. excl. Mengenillidae and Corioxenidae (bs 1). Tarsomeres not shortened, ventral plane distally elongated (37.2, CI 0.75), all tarsomeres with hairy soles
(38.2, CI 0.5)
Fig. 4 Strepsiptera phylogeny, strict consensus tree of 15 minimal
Dundoxenos + Malayaxenos (Corioxenidae) (bs 3). Mandibles
largely reduced (21.2, CI 0.667), sensorial spots on tarsomeres
1–3 (39.1), abdominal segment IX ventrally elongated (41.1),
aedeagus elongated (43.1)
length trees obtained in the initial analysis (all characters unweighted
and unordered, uninformative characters excluded). The genus
Mengenilla and a clade comprising Halictophagus + (Elenchus + Xenos
+ Stichotrema + Stylops) are monophyletic in all trees when characters
7, 22, 29, 33, 38 and 46 are treated as ordered.
Elenchus + ( Xenos + Stylops + Stichotrema) (bs 1). Antennomeres 4 + 5 fused (12.1, CI 0.5), antennomere 4 not flabellate
(16.0, CI = 0.5), sensorial spot present on tarsomere 1 (39.2)
of the latter three taxa seems to be well supported by features
of the primary larvae ( Pohl 2002: e.g. setae on labial palps
absent, intercoxal sternites broad).
In group clades and apomorphies (preferred tree, unambiguous characters only, consistency index [CI ] = 1 unless otherwise noted; all listed states except for those of character 37 are
equally placed in all six trees):
Xenos + Stylops + Stichotrema (bs 0). All tarsomeres shortened,
± triangular, ventral plane distally elongated (37.3, CI
0.750)
Discussion
Strepsiptera s.l. ( branch support 10 [ = bs ]). Ommatidia distinctly
separated (‘raspberry eyes’) (4.1), antennomere 3 flabellate (15.1),
antennomere 4 flabellate (16.1; CI = 0.5), lacinia absent (24.1),
maxillary palp one-segmented (25.1), sensorial groove of
maxillary palp (26.1, CI = 0.5), mesothoracic halteres (28.1),
hindwings slightly longer than wide (29.1), scuto-praescutal
region strongly arched (32.0, CI = 0.5), metapostnotum platelike, about as long as broad (33.1), pro- and mesotrochanter
fused with femur (34.1), segment IX strongly sclerotized
(40.1, CI = 0.5), Tergite X prominent and elongate (42.1)
Strepsiptera s.l. excluding Protoxenos janzeni gen. et sp. nov. (bs 5).
Size less than 7 mm (1.2), dorsomedian frontal impression (5.1),
coronal suture strongly shortened or membranized (6.1,
CI = 0.5), 7 antennomeres or less (10.2), hindwings wider than
long (29.2), metapostnotum elongated and shield-like (33.2),
sternites more heavily sclerotized than tergites (45.1, CI 0.5)
64
Strepsiptera is undoubtedly a monophyletic group, characterized by many autapomorphies (Kinzelbach 1981, 1990;
Kristensen 1981, 1999). However, despite several recent
efforts to clarify its systematic position (Whiting et al. 1997;
Wheeler et al. 2001; Beutel & Gorb 2001), the issue remains
open (Kristensen 1999). The discovery of Protoxenos janzeni
gen. et sp. nov. does not solve the ‘Strepsiptera problem’, but
is nevertheless important in this context, as it allows a reevaluation of the groundplan of the Order. In the following,
we discuss characters which must be re-considered in the light
of the new fossil.
Protoxenos janzeni is a typical strepsipteran in its overall
morphology, but displays a number of characters that are
clearly more plesiomorphic than in the hitherto known fossil
and extant members of the Order. Features shared by P.
janzeni and other strepsipterans are the following (marked
with an asterisk if presumably plesiomorphic):
Zoologica Scripta, 34, 1, January 2005, pp57– 69 • © The Norwegian Academy of Science and Letters
H. Pohl et al. • Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber
Fig. 5 Strepsipteran phylogeny, preferred tree of six minimum length cladograms obtained in the analysis with six characters treated as ordered
(7, 22, 29, 33, 38, 46), unambiguous apomorphies mapped on trees (84 steps, CI: 0.7381, HI: 0.2857, RC: 0.6160; uninformative characters
excluded). The numbers above the rectangles refer to character numbers, the numbers below to character states. Only char. 37 is not equally
placed in all minimum length trees.
(1) The scapus and pedicellus of the antennae are short and
cylindrical (*), and the flagellomeres bear very long lateral
processes (flabella).
(2) The ommatidia are comparatively large and separated
by microtrichia (schizochroal eye; Buschbeck et al. 1999).
(3) The maxillae are simplified, without separate cardo and
lacinia, and with a one-segmented palp.
(4) The pro- and mesothorax are very short; in contrast the
metathorax is strongly enlarged.
(5) The forewings are transformed into structures resembling dipteran halteres (but larger).
(6) The hindwings lack transverse veins.
(7) The legs of the pro- and mesothorax possess large and
free coxae (*).
(8) The trochanter and femur are fused.
(9) The coxae of the hindlegs are integrated into the
metathorax.
(10) The metatrochanter is free (*).
(11) The tarsi are five segmented with double claws (*).
(12) The abdomen consists of 10 segments (*).
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
(13) Abdominal segment IX is shortened, heavily sclerotized
and bears the aedeagus; segment X is cylindrical and elongated.
Protoxenos janzeni differs from the known strepsipterans in
the following set of characters.
Body size
Protoxenos janzeni is the largest male strepsipteran with an approximate total body length of 7.6 mm. The size of males varies
between 1.5 and 6 mm according to Kathirithamby (1989) and
between 1.0 and 7.5 mm according to Kinzelbach (1978). The
length of 7.5 mm ascribed to Mengenilla chobauti (Kinzelbach
1978: 35) is a typing error — the maximum size of this species
is 5.7 mm according to Silvestri (1943) and Kinzelbach (1969).
Besides the greater length, the body of P. janzeni is also more
compact in comparison to previously known strepsipterans.
Head capsule
The head capsule is heavily sclerotized. In contrast to presumably basal extant strepsipterans, which are characterized
65
Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber • H. Pohl et al.
by a subprognathous head (e.g. Mengenilla, Beutel & Pohl in
press; position of mouthparts oblique) the head is clearly
orthognathous. In lateral aspect the mandibles and maxillae
are ventrally directed. Due its bending in a ventro-caudal
direction, the head appears hypognathous.
A typical coronal suture is present. The coronal suture of
known strepsipterans is extremely short, transformed into a
short endocarina (Mengenilla), or membranized (Kinzelbach
1971a). New investigations into basal Strepsiptera (E. laboulbenei,
Mengea tertiaria, Mengenilla spp.) have shown that a typical
coronal suture is not present in these taxa (Beutel & Pohl in
press.).
The dorsomedian frontal impression, which is characteristic
for extant strepsipterans and Mengea is absent in P. janzeni.
The antennal insertion is located on the lateral side of the
head capsule. In contrast, the antennal sockets of Mengea and
extant strepsipterans are located on the dorsal side.
Antenna
The antenna of P. janzeni is composed of eight antennomeres.
Antennae with seven antennomeres were hitherto considered
to be a groundplan feature of Strepsiptera (Kinzelbach 1971a,
1990; Kathirithamby 1989). This condition is found in
Mengeidae, Corioxenidae, Halictophagidae, Myrmecolacidae and Bohartillidae (Kinzelbach 1971a), and may be the
result of reduction (apical antennomere) or of fusion (two
distal segments). According to Kinzelbach (1971a), a lower
number, i.e. less than seven, is always due to the fusion of
antennomeres and not to loss of segments.
Labrum
A large free labrum is absent in all extant strepsipterans. A
small triangular or elongate and acuminate structure inserting below the anterior clypeal margin in Australian species of
Mengenilla probably represents a vestigial labrum (Kathirithamby 1991: fig. 36.9A; Beutel & Pohl in press.). A large free
labrum is also known in Mengea (Ulrich 1927; Kinzelbach
1971a; pers. observ.), which is probably a symplesiomorphy
with P. janzeni. In frontal view, the labrum of Mengea is trapezoid. The presence of two lateral processes of the labrum of
P. janzeni is regarded as an autapomorphy of this taxon.
Mandible
The mandibles of P. janzeni are more robust and distinctly
broader at base than those of basal extant Strepsiptera. Moreover, in contrast to mandibles of other representatives of the
group, they are distinctly bent inwards. It is likely that a
primary and secondary joint is present in P. janzeni, whereas
typical anterior and posterior articulations are absent in extant
strepsipterans (Beutel & Pohl in press.). A comparatively
plesiomorphic condition is preserved in Mengea and Eoxenos,
where the mandibular base is closely adjacent with the clypeus
66
anteriorly and with the maxillary base posteriorly. The
mandibles of P. janzeni appear to be suitable for feeding. This
is not the case in extant strepsipterans; the males of some taxa
have been observed using them to remove the cephalotheca
of the puparium (Grabert 1953; Kinzelbach 1971b).
Maxilla
In its general design, the maxilla is similar to that of other
strepsipterans (without separate cardo and lacinia, with onesegmented palp). In some strepsipterans (e.g. Mengenilla
kaszabi, Dundoxenos breviphlebos; Kinzelbach 1969; Pohl et al.
1996) the palp originates in a subterminal position on the
stipital part of the maxilla, but this has nothing to do with the
presence of a subapical mesal process in P. janzeni (in addition
to the terminally inserted palp). It is very likely that this lobe
represents the galea. A slot-like sensorial pit is present on the
lateral side of the palp of P. janzeni (and also in Mengea and
Eoxenos). It is missing in all other strepsipterans (Beutel &
Pohl in press).
Metathorax
A striking difference between Mengea and extant strepsipterans on one hand and P. janzeni on the other is the transverse
metapostnotum in the latter taxon (not shield-like). A posteromedian extension that usually covers the median part of
several abdominal tergites is not developed. The alinotum is
almost twice as long as the postnotum and postlumbium (ratio
alinotum: postnotum + postlumbium = 1.7 : 1).
Hindwings
The hindwings of P. janzeni are moderately extended in a rostrocaudal direction and are intermediate between a ‘regular’
insect wing and the typical fan-shaped strepsipteran hindwings, which are very distinctly extended rostrocaudally. The
venation pattern does not show any distinctive differences.
Transverse veins are completely missing. A cell formed by
MA2 and CuA1, as present in Mengea, is absent in P. janzeni
(Fig. 3B). Kinzelbach (1978) suggested that this cell may be
simply a fold, which extends between the end of CuA1 and
MA2. However, additional specimens of M. tertiaria with wellpreserved hindwings (four specimens HLMD, one specimen
private collection of R. Kinzelbach) confirm the earlier finding (Menge 1866; Ulrich 1927; Keilbach 1939).
Abdomen
The tergites and sternites are equally sclerotized. The sternites are more strongly sclerotized in all other strepsipterans.
Conclusions
The results of this study support the monophyly of Strepsiptera s.l., Strepsiptera excl. P. janzeni and Strepsiptera s.s.
There is no good reason to doubt the monophyly of extant
Zoologica Scripta, 34, 1, January 2005, pp57– 69 • © The Norwegian Academy of Science and Letters
H. Pohl et al. • Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber
Strepsiptera. However, the group is not supported by many
autapomorphies. One important derived feature is the reduced
labrum. Besides this, the fossil genus Mengea is very similar
to extant strepsipteran taxa and already strongly reduced in
size.
Strepsiptera s.s. excl. Eoxenos is well supported, implying
paraphyly of Mengenillidae; the latter are mainly characterized
by one plesiomorphic feature, the free-living females. A major
step in the evolution of Strepsiptera is the rise of Stylopidia.
They are well supported by different character transformations of males (modifications of the distal leg segments, loss
of six spiracles). However, the most striking feature is the
endoparasitism of the adult females. The fact that the basal
strepsipteran groups (P. janzeni, Mengeidae, Mengenillidae)
are represented by only 3% of the described species underlines the importance of this evolutionary change. There is no
direct fossil evidence, but it is very likely that the females of
P. janzeni and Mengeidae were free living as in extant Mengenillidae. This is strongly suggested by the lack of specialized adhesive hairs on the tarsi of P. janzeni and Mengea (and
Mengenillidae). These structures are used by males of Stylopidia to attach to the host of the parasitic females (Pohl &
Beutel 2004). Together with a hook-shaped aedeagus in ‘higher’
Stylopidia, they provide sufficient adhesion to penetrate the
exposed female cephalothorax and stay on the host as long as
possible.
The data presented in this study are not sufficient for a
clarification of interrelationships within Stylopidia. Some of
the character states relevant to the ‘higher’ groups (chars. 35,
37, 44) are not equally placed in all cladograms. However, the
monophyly of some clades (Corioxenidae, Stylopiformia incl.
Elenchus, Halictophagidae + [Xenidae + Myrmecolacidae +
Stylopidae]) (e.g. Pohl 2002) was confirmed and seems to be
well supported. Autapomorpies of male Stylopiformia are the
modified shape of the tarsomeres and the presence of hairy
soles on the ventral side of all of them. However, the most
striking evolutionary novelty of this clade is the birth opening
of the endoparasitic females.
The discovery of P. janzeni increases our knowledge of the
ancestral character states of Strepsiptera. Newly established
groundplan features are the presence of a normally developed
coronal suture, absence of a dorsomedian impression of the
head, a large free labrum, laterally inserted eight-segmented
antennae, robust mandibles with a broad base, presence of a
galea, transverse metapostnotum, tarsi without adhesive hairs,
and equally sclerotized tergites and sternites of the abdomen.
The presence of dagger-like mandibles in Strepsiptera and
Antliophora was considered to be a potential synapomorphy
by Whiting et al. (1997), although this interpretation now
seems doubtful in view of the condition in P. janzeni. Crowson
(1960) believed the more extensive sclerotization of the
abdominal sternites, compared to that of the tergites, to be a
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
possible synapomorphy of Strepsiptera and Coleoptera, while
the presence of specialized adhesive hairs on the tarsomeres
was considered to be a shared derived feature of both groups
by Beutel & Gorb (2001). Our findings supersede these
interpretations.
Acknowledgements
Thanks are due to the following persons and institutions.
J.-W. Janzen (Seevetal) made his specimen available for study.
Dr W. Schneider (Hessisches Landesmuseum Darmstadt)
loaned specimens of P. janzeni and M. tertiaria. A. Slipinski
(Australian National Insect Collection, CSIRO Canberra)
loaned Australian specimens of Mengenilla. Prof Dr A.
Buschinger (TU Darmstadt) generously allowed us to use
his microscopic equipment. We are also indebted to two
anonymous reviewers for valuable comments.
References
Beutel, R. G. & Gorb, S. (2001). Ultrastructure of attachment
specializations of hexapods (Arthropoda): evolutionary patterns
inferred from a revised ordinal phylogeny. Journal of Zoological
Systematics and Evolutionary Research, 39 (4 ), 177–207.
Beutel, R. G. & Pohl, H. (in press). Head structures of males of
Strepsiptera (Hexapoda) with emphasis on basal splitting events
within the order. Journal of Morphology.
Buschbeck, E., Ehmer, B. & Hoy, R. (1999). Chunk versus point
sampling: visual imaging in a small insect. Science, 286, 1178 –1180.
Colless, D. H. & McAlpine, D. K. (1991). Diptera ( Flies). In CSIRO
( Ed.) The Insects of Australia, Vol. 2 ( pp. 717–786). Carlton, Victoria:
Melbourne University Press.
Crowson, R. A. (1960). The phylogeny of Coleoptera. Annual Review
of Entomology, 5, 111–134.
Grabert, B. (1953). Bau der Geschlechtsorgane und Kopulation
beim Stylops-Männchen ( Insecta, Strepsiptera). Diplomarbeit,
Berlin: Freie Universität, Berlin.
Grimaldi, D., Agosti, D. & Carpenter, J. C. (1997). New and rediscovered primitive ants (Hymenoptera: Formicidae) in Cretaceous
amber from New Jersey, and their phylogenetic relationships.
American Museum Novitates, 3208, 1– 43.
Kathirithamby, J. (1989). Review of the order Strepsiptera. Systematic
Entomology, 14, 41–92.
Kathirithamby, J. & Grimaldi, D. (1993). Remarkable stasis in some
Lower Tertiary parasitoids: descriptions, new records, and review
of Strepsiptera in the Oligo-Miocene amber of the Dominican
Republic. Entomologica Scandinavica, 24, 31– 41.
Keilbach, R. (1939). Neue Funde des Strepsipterons Mengea tertiaria
Menge im baltischen Bernstein. Bernstein-Forschungen, 4, 1–7.
Kinzelbach, R. (1969). Die männlichen Imagines der Mengenillidae
und Mengenilla kaszabi n. sp. — Ergebnisse der zoologischen
Forschungen von Dr. Z. Kaszab in der Mongolei (Strepsiptera,
Insecta). Reichenbachia, 12, 217–247.
Kinzelbach, R. K. (1971a). Morphologische Befunde an Fächerflüglern
und Ihre Phylogenetische Bedeutung ( Insecta: Strepsiptera). Stuttgart:
Schweizerbart’sche-Verlagsbuchhandlung.
Kinzelbach, R. (1971b). Strepsiptera (Fächerflügler). In J.-G. Helmcke,
D. Starck & H. Wermuth (Eds) Handbuch der Zoologie, Vol. 4
(pp. 1–73). Berlin, New York: Walter de Gruyter.
67
Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber • H. Pohl et al.
Kinzelbach, R. (1978). Fächerflügler (Strepsiptera). Jena: Gustav Fischer.
Kinzelbach, R. (1981). Strepsiptera. In W. Hennig (Ed.) Insect
Phylogeny (pp. 308–314). Chichester: John Wiley & Sons.
Kinzelbach, R. (1990). The systematic position of Strepsiptera
(Insecta). American Entomologist, 35, 292–303.
Kinzelbach, R. K. & Lutz, H. (1985). Stylopid larva from the Eocene
— a spotlight on the phylogeny of the stylopids (Strepsiptera).
Annals of the Entomological Society of America, 78, 600 – 602.
Kinzelbach, R. & Pohl, H. (1994). The fossil Strepsiptera ( Insecta:
Strepsiptera). Annals of the Entomological Society of America, 87, 59 –
70.
Kristensen, N. P. (1981). Phylogeny of insect orders. Annual Reviews
of Entomology, 26, 135 –157.
Kristensen, N. P. (1999). Phylogeny of endopterygote insects, the
most successful lineage of living organisms. European Journal of
Entomology, 96, 237–253.
Labandeira, C. C. (1994). A compendium of fossil insect families.
Milwaukee Public Museum Contributions in Biology and Geology, 88,
1–71.
Lutz, H. (1990). Systematische und palökologische Untersuchungen
an Insekten aus dem Mittel-Eozän der Grube Messel bei Darmstadt. Courier Forschungsinstitut Senckenberg, 124, 1–164.
Maddison, W. P. & Maddison, D. R. (2000). MacClade, Version 4.0:
Analysis of phylogeny and character evolution. Distributed by Sinauer
Associates. Inc.
Menge, A. (1866). Uber ein Rhipidopteron und einige Helminthen
im Bernstein. Schriften der naturforschenden Gesellschaft zu Danzig,
2, 1–8.
Pohl, H. (2002). Phylogeny of the Strepsiptera based on morphological data of the first instar larvae. Zoologica Scripta, 31, 123 –134.
Pohl, H. & Beutel, R. G. (2004). Fine structure of adhesive devices
of Strepsiptera ( Insecta). Arthropod Structure and Development, 33,
31–43.
Pohl, H., Katbeh-Bader, A. & Schneider, W. (1996). Description of
a new genus and two new species of Corioxenidae from Jordan
(Insecta: Strepsiptera). Zoology in the Middle East, 13, 107–119.
Pohl, H. & Kinzelbach, R. (1995). Neufunde von Fächerflüglern aus
dem Baltischen und Dominikanischen Bernstein (Strepsiptera:
Bohartillidae & Myrmecolacidae). Mitteilungen des GeologischPaläontologischen Instituts der Universität Hamburg, 78, 197–209.
Pohl, H. & Kinzelbach, R. (2001). First record of a female stylopid
(Strepsiptera: ? Myrmecolacidae) parasite of a prionomyrmecine
ant (Hymenoptera: Formicidae) in Baltic amber. Insect Systematics
& Evolution, 32, 143 –146.
Silvestri, F. (1943). Studi sugli ‘Strepsiptera’ Insecta. III. Descrizione
e biologia di 6 specie italiane di Mengenilla. Bollettino del Laboratorio
di Zoologia generale e agraria della Facoltà Agraria in Portici, 32, 197–
282.
Swofford, D. L. (2002). PAUP*: Phylogenetic analysis using parsimony
(and other methods), Version 4.0 b10. Distributed by Sinauer Associates. Inc.
Ulrich, W. (1927). Über das bisher einzige Strepsipteron aus dem
baltischen Bernstein und über eine Theorie der Mengeinenbiologie. Zeitschrift für Morphologie und Ökologie der Tiere, 8, 45– 62.
Wheeler, W. C., Whiting, M., Wheeler, Q. D. & Carpenter, J. C.
(2001). The phylogeny of the extant hexapod orders. Cladistics, 17,
113–169.
Whiting, M. F., Carpenter, J. C., Wheeler, Q. D. & Wheeler, W. C.
(1997). The Strepsiptera problem: Phylogeny of the holometa-
68
bolous insect orders inferred from 18S and 28S ribosomal DNA
sequenes and morphology. Systematic Biology, 46, 1– 68.
Appendix 1
List of characters used in the analysis (adult males only). The
presumably plesiomorphic condition is coded as 0 even
though this traditional convention is inconsequential in cladistic analyses with a posteriori polarity assessment.
1. Size: (0) more than 10 mm; (1) 7–8 mm; (2) 6 mm or less.
Generally, size reduction is a problematic feature in insect
systematics. However, in the case of Strepsiptera it appears
to be a meaningful character. Protoxenos is distinctly larger
and more robust than all other known species, and there is
apparently no reversal leading to a size exceeding that of
the presumptive groundplan condition of Strepsiptera s.l.
(including stem lineage).
Head
2. Tentorium: (0) present; (1) absent.
3. Gula: (0) absent; (1) present.
4. Compound eyes: (0) ommatidia not distinctly separated;
(1) distinctly separated by microtrichia.
5. Dorsomedian frontal impression: (0) absent; (1) present.
6. Coronal suture: (0) present as a typical ecdysial suture;
(1) extremely short or membranized.
7. Labrum: (0) free, normally sized; (1) present, but distinctly reduced or narrowed; (2) absent. It is very likely that
the vestigial labrum of Australian Mengenilla species is an
intermediate stage, leading to complete absence. Therefore
the character is used as ordered in the second analysis.
8. Paired anterior processus of labrum; (0) absent; (1) present.
9. Antennal insertion: (0) laterally, anterior to compound eye;
(1) dorsal side of head.
10. Number of antennal segments: (0) more than eight
segments; (1) eight segments; (2) seven segments or less.
11. Antennomeres 3 + 4 fused; (0) absent; (1) present.
12. Antennomeres 4 + 5 fused; (0) absent; (1) present.
13. Antennomeres 5 + 6 fused; (0) absent; (1) present.
14. Antennomeres 6 + 7 fused: (0) absent; (1) present.
15. Lateral process (‘flabellum’) of antennomere 3: (0) absent;
(1) present.
16. Lateral process of antennomere 4: (0) absent; (1) present.
17. Lateral process of antennomere 5: (0) absent; (1) present.
18. Lateral process of antennomere 6: (0) absent; (1) present.
19. Lateral process of antennomere 7: (0) absent; (1) present.
20. Sensorial groove of antennomere 4 (possibly pressure
sensor [Hofeneder’s organ]): (0) absent; (1) present.
21. Mandibles: (0) present, normally developed; (1) distinctly
reduced, cone-shaped; (2) absent or vestigial.
22. Mandibular base: (0) broad, closely adjacent with head
capsule; (1) broad, closely adjacent with head capsule, but
secondary mandibular joint indistinct or absent; (2) distinctly
Zoologica Scripta, 34, 1, January 2005, pp57– 69 • © The Norwegian Academy of Science and Letters
H. Pohl et al. • Protoxenidae fam. nov. ( Insecta: Strepsiptera) from Baltic amber
narrowed, separated from head capsule by membranous area.
The distinctly narrowed mandibular base, which is found in
almost all extant strepsipterans, has almost certainly evolved
via the condition found in Eoxenos, with the base still broad
but with a reduced secondary mandibular joint. The character
is used as ordered in the second analysis.
23. Galea: (0) present; (1) absent.
24. Lacinia: (0) present; (1) absent.
25. Maxillary palp: (0) composed of more than two palpomeres; (1) all palpomeres fused.
26. Sensorial groove of maxillary palp: (0) absent; (1) present.
27. Labial palps: (0) present; (1) absent.
Thorax
28. Mesothoracic halteres: (0) absent; (1) present.
29. Shape of hindwings: (0) distinctly longer than wide; (1)
slightly longer than wide; (2) wider than long. It is very likely
that the typical fan-shaped hindwings of Mengea and extant
strepsipterans are derived from a condition found in males of
Protoxenos. The character is therefore used as ordered in the
second analysis. The halteres of Diptera are longer than wide.
However, they are not only reduced wings, but specialized
sense organs; this function may have had an effect on the shape.
Therefore this character is coded as inapplicable for Tipula.
30. Transverse veins of alae: (0) present; (1) absent.
31. Cells of alae: (0) more than one; (1) one; (2) absent.
32. Scuto-praescutal-region of metathorax: (0) strongly arched
and distinctly protuding; (1) weakly arched or triangular and
not protuding.
33. Metapostnotum: (0) external part transverse; (1) external
part plate-like, about long as broad; (2) external part shield-like,
distinctly longer than broad, covering median part of several
abdominal tergites. The typical shield-like metapostnotum
of Mengea and extant strepsipterans has almost certainly
evolved via a condition found in Protoxenos. The character is
used as ordered in the second analysis.
34. Trochanter and femur of fore- and middle legs: (0) separate; (1) fused.
35. Number of tarsomeres: (0) five; (1) four; (2) three; (3) two.
36. Claws: (0) strong pair; (1) weak pair; (2) none.
© The Norwegian Academy of Science and Letters • Zoologica Scripta, 34, 1, January 2005, pp57– 69
37. Shape of tarsomeres: (0) all tarsomeres rod-like, at least
2× as long as broad; (1) morphological tarsomere 4 shortened,
about as broad as long or broader; (2) tarsomeres not
shortened, ventral plane distally elongated; (3) all tarsomeres
shortened, ± triangular, ventral plane distally elongated.
38. Hairy adhesive soles of tarsomeres: (0) absent; (1) present
in tarsomere 4; (2) present in all tarsomeres. It is likely that
this condition has evolved in tandem with the adoption of
permanent endoparasitism by females in order to provide
sufficient adhesion during copulation, which takes place on
the host. It is very unlikely that a secondary reduction has
occurred in Corioxenidae. Therefore the character is used as
ordered in the second analysis.
39. Sensorial spots of tarsi: (0) absent; (1) present in tarsomeres 1–3; (2) present in tarsomere 1.
Abdomen
40. Sclerotization of abdominal segment IX: (0) weak; (1) strong.
41. Shape of abdominal segment IX: (0) not elongated;
(1) ventrally elongated.
42. Tergite X: (0) strongly reduced or absent; (1) prominent
and elongated.
43. Size of aedeagus: (0) short; (1) elongated. The homology
of the external male genitalia in Diptera is problematic (e.g.
Colless & McAlpine 1991). Therefore we have coded this
and the following character as inapplicable for Diptera.
44. Shape of aedeagus: (0) straight; (1) hook- or anchor-like;
(2) with two pairs of rounded lobes and slender apex.
45. Sclerotization of tergites and sternites of abdomen:
(0) equal; (1) sternites more heavily sclerotized than tergites.
46. Abdominal spiracles: (0) segments I–VIII; (1) segments
I–VII; (2) segment I. The reduction of abdominal spiracles in
Stylopidia has almost certainly evolved with the adoption of
permanent endoparasitism of the male larvae. The last larval
instar extrudes only the head, thorax and first abdominal
segment through the host cuticle. The only spiracle of the
last larval instar is abdominal spiracle I. It is likely that this
condition is maintained in the adult stage (paedogenesis). As
it is likely that the loss of spiracle VIII is an intermediate
state, the character is used as ordered in the second analysis.
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